1 UNIT I 1 UNDERSTANDING JAVA EE Unit Structure 1.1 Objectives 1.2 Introduction to Java EE 1.3 Basic Concepts related Java EE 1.3.1 Specification of Java EE 1.3.2 Wha t is an Enterprise Application 1.3.3 What is java enterprise edition 1.3.3.1 Business [ Model] 1.3.3.2 Présentation [View] 1.3.3.3 Persistence layers(Controllers) 1.3.4 Java EE Technologies 1.3.5 Java EE evolution 1.3.6 Glassfish Server 1.4 Questions 1.5 Summary 1.6 Reference for further reading 1.1 OBJECTIVES 1) Java EE Provides More Flex ible Technology. 2) Java EE is a collection of API where students/professionals are able to design server side applications. 3) Students/professionals are able to originally design and develop applications in a thin -client -tiered environment. 4) Java EE application s are hosted on application servers ( WebSphere, GlassFish, WildFly, Apache Tomcat etc….) 5) When we design & develop Java EE applications to use popular design patterns [ MVC]. 6) Java EE support for Enhanced Extensibility. 7) Java EE provides a powerful API for Strong and Dynamic Web Programming.
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Enterprise Java 2 1.2 INTRODUCTION TO JAVA EE The Java EE stands for Java Enterprise Edition, which was earlier known as J2EE and is currently known as Jakarta EE in JDK latest version. The Java EE provides a platform for Student/profe ssionals with enterprise features including - distributed computing and web services. Java EE types of applications are usually run on microservers or application servers. Areas where Java EE is used are e -commerce, accounting, banking information systems. 1.3 BASIC CONCEPTS RELATED TO JAVA EE 1.3.1 Specification of Java EE: Java EE has various specifications which are useful in Designing & Developing applications and web pages, reading and writing from the database in various transactional ways and also managing distributed queues in network communication. Java EE API such as Enterprise JavaBeans, connectors, Servlets, Java Server Pages and various web services. 1.3.2 What is an Enterprise Application? : In Java EE we can design the Enterprise /Business/C ommercial level Applications. Java EA is a large software system platform designed to operate in a corporate / business or government level environment. Java EE Applications are complex,scalable, component -based, distributed and mission critical. Java EA consists of a large number of programs with shared business applications and organizational modeling utilities designed for unparalleled functionalities. Enterprise Application’s software is a critical component of any computer - based information system. E nterprise level Application software ultimately enhances their efficiency and productivity through various levels of functionality in business. 1.3.3 What is java enterprise edition? : Java EE frameworks provide common design patterns rarely used in develop ment of Java EE Application, and add into reusable class libraries. These class libraries are implemented to access the database for various processing ways - security, transaction processing, screen layout, data validation,object construction, caching, a nd other development/Programming related tasks so that Java EE developers can focus on the purely business logic . munotes.in
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Understanding Java EE 3
1.3.3 A Figure shows Java EE Architecture. Above Figure indicate flow of java EE applications first layer as an client where they can be s end & receive responses from server side(Java Enterprise Edition Programs) ,second layer is an middle Tier [Combination of java’s web enabled API’s] where it can be acting as a Controller of client & Database . Java Enterprise Edition (Java EE) technology provides services to enterprise applications using a multi -layer architecture. Java EE applications/projects are web -enabled and Java based, which means they may be written once and deployed on any container supporting the powerful execution in Java EE en vironment. Following are The three most common Java EE design patterns also known as MVC model focus on: 1) business(Model) 2) presentation(View) 3) persistence layers(Controllers). 1.3.3.1 Business [Model]: Model/Business Logic represents an object or JAVA POJO[purely old java object] carrying data. It can also have logic to update controllers if its data changes vary to Action.Model represents the state of the application i.e. data. Model containing business logic. 1.3.3.2 Presentation [View]: View represents the visualization of the data and represents on the user screen that model contains processed data/result oriented. View is an represents the presentation i.e. UI(User Interface)/front end.. 1.3.3.3 Persistence layers [Controllers]: Controllers are handled on both model and view. It controls the data flow into the model object and updates the view whenever data changes/requirements change . It keeps view and model separate. munotes.in
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Enterprise Java 4 In MVC Controller acts as an interface/Intermediate between View and Model. Controller Handling all the incoming requests from Model & View as per request redirect to automatically as per request & response preference .
1.3.3 A Figure shows Java EE design patterns Communication.
1.3.3 B Figure shows Java EE design patter ns Communication[MVC]. 1.3.4 JAVA EE TECHNOLOGIES. Java EE is actually a collection of various technologies and API[Application Programming Interface] for the Java EE platform designed & Developed to support "Enterprise" levels Applications which can ge nerally be classed as large -scale, Multi -tier , distributed, transactional and highly -available applications designed to support mission -critical/handling critical processes in business requirements. ● Following are list of java EE Technologies: 1. JDBC: JDBC stands for Java Database Connectivity.JDBC is a Java API used to connect and execute the sql query with their relevant database. JDBC can munotes.in
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Understanding Java EE 5 handle backend & frontend transactions the JDBC API uses JDBC drivers to connect with the database/backend to fron t end or java application .
Fig: shows JDBC for Database connectivity with java application. There are four types of JDBC drivers: A) JDBC -ODBC Bridge Driver. B) Native Driver. C) Network Protocol Driver. D) Thin Driver. 2. JNDI: Java Naming and Directory Interface is the name of the interface in the Java programming language. It is an API( Application Program Interface) that works with servers for fetching files from a database using naming conventions. The naming convention(Name of class,interface etc….) can be a single phrase or a word. It can also be incorporated in a socket to implement socket programming, using servers transferring data files or flat files in a project. JNDI is used in web pages in browsers/clients where there are instances of many directories/files. JNDI provides users in Java related various facilities to search objects in Java using the Java coding language.
Fig: shows Architecture of JNDI. munotes.in
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Enterprise Java 6 3. EJB: EJB stands for Enterprise Java Bean. It is a specification provided by Sun Micros ystems/Oracle corporation or IBM to develop robust,secure and scalable distributed applications using Java EE. To run the Java EJB applications, you should install an application server (EJB Container) such as Weblogic,Jboss,Websphere, Glassfish etc. It performs Following Transaction of EJB application: 1. life cycle management. 2. security. 3. transaction management. 4. object pooling. ● Use of EJB: 1) EJB Application needs Remote Access. In other words, it is distributed. 2) EJB Application needs to be scalable. Java EJB a pplications support load balancing, clustering and fail -over. 3) EJB Application needs encapsulated business logic. Java EJB application is separated from presentation and persistent layer. ● Types of Enterprise Java Bean : There are 3 types of enterprise beans in java. 1) Session Bean : Session bean contains business logic that can be invoked by local, remote or web service clients/browsers. 2) Message Driven Bean : Message Driven Bean also Like Session Bean, it contains the business logic but it is invoked by pas sing messages/message communication. 3) Entity Bean : IN Entity Bean It encapsulates the state that can be persisted in the database. Currently it is known as or it is replaced with JPA (Java Persistence API). 4) RMI: The RMI (Remote Method Invocation) is an API that provides a mechanism to create distributed applications in java. The RMI allows an object to invoke methods on an object running in another JVM. munotes.in
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Understanding Java EE 7 The RMI provides remote communication between the applications using two objects stub and skeleton. ● Understanding stub and skeleton : In client server communication RMI uses stub and skeleton objects for communication with the remote object for both objects are accessing purpose . Note: A remote object is an object whose method can be invoked from anothe r JVM. Let's understand the stub and skeleton objects: 1) stub: The stub is an object, acts as a gateway for the client side. All the outgoing requests are routed through it. It resides at the client side and represents the remote object. When the caller invokes method on the stub object, it does the following tasks: 1. It implement a connection with remote Virtual Machine (JVM), 2. It writes and transmits (marshalls) the parameters to the remote Virtual Machine (JVM), 3. It waits for the result from the remote JVM . 4. Stub reads (unmarshalls) the return value or exception. 5. Stub finally returns the value to the caller . 2) skeleton: The skeleton is an instance/object, and acts as an interface for the server side object. All the incoming requests are routed through sk eleton. When the skeleton receives the incoming request, it does the following operations: 1. Skeleton reads the parameter for the remote method. 2. Skeleton invokes the method on the actual remote object as per communication. 3. Skeleton writes and transmits (marshalls) the result to the caller. munotes.in
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Enterprise Java 8
Fig: Shows communication of stub & skeleton. 5) JSP: In Java EE uses JSP technology to create web applications just like Servlet technology. It can be treated as an enhancement to Servlet because it provides more f unctionality than servlet such as expression language, JSTL, etc. In the JSP page containing HTML tags and JSP tags. The JSP pages are easier to maintain than Servlet because we can separate the code of designing and development. It provides some addition al features such as implicit objects,Expression Language, Custom Tags, etc. 6) Java servlets: Servlet technology is used to create a web application (Executes/resides on server side and generates a dynamic web page & response to browser). Servlet is a tech nology that would be robust and scalable because of the Java language. Before Servlet, to use one common interface CGI (Common Gateway Interface) scripting language was common as a server - side programming language. ● What is a Servlet? Following are the Se rvlet can be described in many ways ● Servlet is a technology which is used to create and design a dynamic web application. ● Servlet consists of an API that provides various interfaces and classes. ● Servlet is an interface that must be implemented for creating any Servlet class. ● Servlet is a class that extends the capabilities of the servers and responds to the incoming requests. It can respond to any requests. ● In java EE Servlet is a web component that is deployed on the server to create a dynamic web page. munotes.in
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Understanding Java EE 9
Fig: Using servlet interface implementing client server communication. 7) XML: XML (Extensible Markup Language) is a very popular simple text - based/marked up language that can be used as an interface of communication between different applications. It is considered as a standard technique to transport and store data. JAVA provides excellent support and a rich set of libraries to modify, parse and inquire XML documents. 8) JMS: MS (Java Message Service) is an API that provides the facility to create, send and read messages.JMS is also known as a messaging service. It provides loosely coupled, reliable and asynchronous communication. Use of Java Messaging Service : ● In JMS Service messaging is a technique to communicate applications or software components. ● JMS service is mainly used to send and receive messages from one application to another. ● Generally, the user sends a message to the application. But, if we want to send messages from one application to another, we need to use the JMS API. ● Consider a scenari o, one application A is running in INDIA and another application B is running in the UK. To send a message from A application to B, we need to use JMS. 9) Java IDL: In Java EE IDL stands for (Interface Definition Language) is a technology for distribute d objects -that is, objects can communicate/interact on different platforms across a network. Java IDL is similar to RMI (Remote Method Invocation), But in IDL which supports distributed objects written entirely in the Java programming language. munotes.in
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Enterprise Java 10 10) JTS: In Java The JTS stands for Java Topology Suite (JTS) is an open source Java API/ library that provides an object model for planar geometry together with a set of fundamental geometric functions. JTS is specifically designed to be used as a core component of vector - based geomatics software such as GIS -Geographical Information Systems. Now JTS also be used as a general -purpose library providing algorithms in computational geometry in java applications. 11 ) JTA: The Java Transaction API (JTA) allows for app lications to perform distributed transactions, that is, transactions that access and update data on two or more networked computer resources. The JTA specifies standard Java interfaces between a transaction manager and the other network component. 12) Java Mail: In Java EE Technology JavaMail is an API that is used to compose, write and read electronic messages i.e (to send & receive emails). These JavaMail API provides services related to protocol -independent and platform -independent frameworks for sendi ng and receiving mail through the network. The javax.mail and javax.mail.activation packages contain the core classes of JavaMail API. 13) JAF: JFA (Java Framework Architecture) is an API included in the Software Development Kit(SDK) for designing software applications in Indian languages. It consists of a set of Java components ,Interfaces and supporting classes which enable the creation of content in Indian scripts(Language). The scripts supported are Devanagari,Oriya , Kannada,Assamese, Bengali, Tamil, Gujarati, Punjabi, Malayalam,Telugu and English. 1.3.5 Java EE evolution: Java EE Formerly called as a J2EE, the first version of Java EE platform was officially released in December 1999 with 10 specifications. Among these specifications, there were Serv lets and JavaServer Pages (JSP) for data presentation, Enterprise JavaBeans (EJB) for the management of persistent data and secure transactions, remote access to business services through RMI -IIOP protocol (Remote Method Invocation over Internet Inter -ORB Protocol), and the JMS (Java Message Service) specification, which was used to send messages. More effort and many contributions, early versions of Java EE were too much complex and difficult to implement because JEE provides more munotes.in
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Understanding Java EE 11 specification than J2EE. This leading to much criticism/complexity of code and caused the rise of competing frameworks such as Spring Framework. 1.3.6 Glassfish Server: GlassFish is an application server/web server started by Sun Microsystems for Java Enterprise Edition which is now owned & managed by Oracle corporation. It is a free software that is released under two free software licenses. The one is a common development and distribution license and the other is GNU general public license. Sun Microsystems launched the project on June 6, 2005. Requirement: 1. JDK must be installed on the system. 2. Windows OS 3. Login as an admin. Steps to Install Glassfish web server in Eclipse: 1. Open Eclipse. 2. Go to Help > Eclipse Marketplace. 3. Search for GlassFish. 4. Click on Install. 5. Glassfish Tools and oracle. eclipse. tools. glassfish is selected. Click Confirm. Steps to configure Glassfish server with eclipse : Step-1 launch Eclipse IDE. Click Window menu > select Show View sub menu > select Servers. munotes.in
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Enterprise Java 12 Or, right click mouse anywhere in the Serve rs page > select New menu > select Server sub menu.
Step-2: in the New Server page, notice in the middle box which list the available servers. We are going to download the Glassfish server which is not in the list. Type the Server’s host name (if neede d). In this case we are using 'localhost'. Then, click the Download additional server adapters link. munotes.in
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Understanding Java EE 13 The Install New Extension wizard will begin, searching available server adapters which are available from the update servers.
Step-3 from the list of available server adapter, select Glassfish server and click Next. munotes.in
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Enterprise Java 14 The download requirements and dependencies process will begin.
After the download requirement and dependencies process is completed, click Next.
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Understanding Java EE 15 Step-4 Accept the license agre ement and click Finish.
Step -5 Click OK for the server adapter download confirmation prompt window.
The Glassfish download and installation will begin. Click Details for the details process. munotes.in
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Enterprise Java 16 The task can be set to be done at the background by cl icking the Run in Background button.
Step-6 restart Eclipse in order the new downloaded and installed Glassfish server take effect.
Step-7 Now, in the New Server page, Glassfish server will be visible in the list of the available servers that are associated with Eclipse and ready to be used. munotes.in
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Understanding Java EE 17
1.4 SUMMARY We can use the Java EE tools for implementing new features in applications that are structured around modules with different purposes, such as web sites, web applications and Enterprise applica tions. When you use Java Enterprise Edition components, you can create distributed, secure applications with transactional support. 1.5 QUESTIONS Q.1 Define java EE? Q.2 Applications of Java EE. Q.3 Explain Design Pattern [MVC] in Java EE. Q.4 Explain wh at technologies are used in Java EE. Q.5 Define Java Enterprise Application. munotes.in
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Enterprise Java 18 Q.6 Explain Servlet & JSP. Q.7 Define Web Server? Q.8 Explain steps to configure glassfish web server in eclipse. Q.9 Define JavaMail API. Q.10 Explain Architecture of JEE. 1.6 RE FERENCE FOR FURTHER READING 1. Java EE 6 Enterprise Architect Exam Guide ,Author: PaulAllen , Publisher: McGraw -Hill 2. The Complete Reference -Java Enterprise Edition (Black Book) ,Author:Herbert schildt. 3. Java EE 7 The Big Picture by - Dr.Danny Co ward Publisher - Oracle press. 4. Advanced Java by -Balaguruswamy . 5. The Java Ee 7 Tutorial by -Ricardo Cervera -Navarro
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19 2 JAVA EE ARCHITECTURE, SERVER AND CONTAINERS Unit Structure 2.1 Objectives 2.2 Introduction to Java EE Architecture 2.3 Types of System Architecture A) Java Enterprise System deployments based Architecture 2.3.1 Logical Tiers Level 2.3.2 Infrastruc ture Service Levels 2.3.3 Quality of Service Level B) Java EE Development Architecture 2.4 Java EE Server 2.5 Java EE Containers 2.6 Questions 2.7 Summary 2.8 Reference for further reading 2.1 OBJECTIVES 1) Java EE Provides Simplified coding Techniq ue. 2) Java EE Provides Flexible Architecture where we can design in various perspective levels.. 3) students/professionals are able to originally design and develop & Deploy their application on server. 4) Java EE Server for implementation of Enterprise Application. 5) Java EE Provides various Containers to transform Business logic etc... 6) Java EE provides a powerful API for Strong and Dynamic Web Programming. 2.2 JAVA ENTERPRISE SYSTEM ARCHITECTURE
Fig: 2.2 Java Enterprise System Architecture. munotes.in
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Enterprise Java 20 A) Java Enterprise System deployments based Architecture: To discuss java EE architectural concepts upon which Java Enterprise System deployments are based. Java Enterprise Edition is a framework in which Java Enterprise System deployment architectures are a nalyzing along with the following three ways/Dimensions: Logical tiers. Infrastructure service levels, Quality of service. These three dimensions, following figure, help to clarify the architectural functions of Java Enterprise System components while de signing and developing projects. In Java EE The three -dimensional framework is the key to designing successful Design & deployment architectures for business software solutions.
Figure 2.3 -A Three Dimensions of Java Enterprise System Architectural Frame work 1) Logical Tiers: In Java EE standard architecture for distributed applications separates application logic into a number of tiers. These tiers signify a logical and physical organization of components into an ordered chain/processing sequence of serv ice providers and consumers in network.
Figure 2.3.1 Logical Tiers for Distributed Enterprise Applications munotes.in
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Java EE Architecture, Server and Containers 21 I) Client Tier: The client tier consists of application logic/Business logic accessed directly by an end user/client side through a user interfac e. The logic in the client tier could include browser -based clients. II) Presentation Tier: The presentation tier consists of application logic/Business logic that prepares data as per request/response for sending to the client tier and processes request s from the client tier to get the back -end business logic as per concern of request & response. The logic in the presentation tier typically consists of J2EE components such as Java Servlet components or JSP components that prepare data for HTML or XML sen ding/receiving or that receive requests for processing from client to server or vice versa. This tier includes various services - secure, personalized, and customized access to business services in the business service tier. III) Business Service Tier: The business service tier consists of actual required Business logic that performs the main functionality of the applications such as processing data, implementing business rules, coordinating multiple users, and managing external resources such as databases or legacy systems as per request & response from the network. In J2EE components can be assembled to deliver complex business services/business processes such as an inventory service or tax calculation service etc. The various implementations of business services encapsulate specific application functionality that can reside and run on a particular computing node/client. IV) Data Tier: The data tier consists of data used by business logic. The data can be persistent application data stored in a database management system. The data can also include data feeds from external sources or data accessible from legacy systems. 2) Infrastructure Service Levels: The interacting software components of distributed enterprise applications require an underlying set of infrastructure services that allows the distributed components to communicate with each other on network communication i.e client to server & server to client, coordinate their work, implement secure access, and so forth. This set of distributed services c onstitutes an infrastructure upon which distributed components can be design & built.
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Enterprise Java 22 Distributed Infrastructure Services: Distributed infrastructure services distributed at many different levels.
Figure 2.3.2 Distributed Infrastructure Service Levels The Infrastructure Service Levels in the above Figure reflect a general dependence of the various distributed services on one another, from the lowest -level operating system services to the highest -level application and integration services in Java Enterpr ise. Following are the list of Levels from bottom to top: I) Operating system platform: It Provides the basic support for any process running on a computing node. The operating system manages physical devices as well as memory, threads, and other resource s necessary to support the Java Virtual Machine . II) Network transport: Network transport Provides basic networking support for communication between distributed application components running on different computing nodes/Network connected different nod es or clients. All These services include support for protocols such as TCP and HTTP/ HTTPS. III) Persistence: It Provides support for accessing/fetching and storing both static data (such as user, directory, or configuration information) and dynamic application data (information that is frequently being updated). VI) Messaging: Messaging Layer Provides support for both synchronous and asynchronous communication between application components in client and server. Synchronous messaging is real -time sendi ng and receipt of munotes.in
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Java EE Architecture, Server and Containers 23 messages; it includes remote method invocation (RMI) between J2EE components and SOAP interactions with web services. Asynchronous messaging is communication in which the sending of a message does not depend on the readiness of the consum er to immediately receive it. Asynchronous messaging specifications, for example, Java Message Service (JMS) and ebXML, It will support guaranteed reliability and other messaging semantics. VII) Runtime: It Provides support required by any distributed com ponent model, such as the J2EE or CORBA models. In addition to the remote method invocation needed for tightly coupled distributed components, runtime services include component state (life -cycle) management, thread pool management, synchronization (mutex locking), persistence services, distributed transaction monitoring, and distributed exception handling. In a J2EE environment, these runtime services are provided by EJB, web, and message -driven bean (MDB) containers in an application server or web server. VIII) Security and policy: Provides support for secure access to application resources. These services include support for policies that govern group or role -based access to distributed resources, as well as single sign -on capabilities. The enhancement o f authentication in Single sign -on allows a user’s authentication to one service in a distributed system to be automatically applied to other services (J2EE components, business services, and web services) in the system. IX) User collaboration: It Provid es services that play a key role in supporting direct communication between users and collaboration among users in enterprise and Internet environments. And also, al l these services are application - level business services, normally provided by standalone s ervers (such as an e-mail server). X) Integration: It Provides the services that aggregate existing business services, either by providing a common interface for accessing them through a network, as in a portal, or by integrating them through a process engine that coordinates them within a production workflow. Integration can also take place as business -to-business interactions between different enterprises/ various enterprise applications. 3) Quality of Service Layer: The previous two architectural Le vels (logical tiers and infrastructure service levels) largely define the logical/business logical aspects of architecture, namely which components are needed to interact in what are the ways where to deliver services to end users/clients. munotes.in
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Enterprise Java 24 As internet and E-commerce services now become more critical to handle business operations/services, scalability, performance, security, availability and serviceability of these services has become a key requirement of large -scale, high -performance deployment architect ures in java enterprise applications. Following are the List of Quality Services required in Java EE Architecture. 1) Performance: To check out measurement of response time and latency with respect to user load conditions. 2) Availability: A measuredly sys tem’s resources and services are accessible to end users/clients, often expressed as the uptime of a desired system. 3) Security: Regarding security, a complex combination of factors that describe the integrity of a system and its users. Security includes authentication and authorization of users as well as the secure transport of information through the network. 4) Scalability: In Enterprise applications the ability to add capacity (and users) to a deployed system over time. Scalability typically involves adding resources to the system but should not require changes to the deployment architecture while designing java applications. B) Java EE Development Architecture: Following are Java EE provides an environment for development and deployment of web -based e nterprise applications using multi -tier architecture.
The above diagram demonstrates J2EE multi -tier architecture that encompasses several J2EE containers each including its own J2EE components. munotes.in
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Java EE Architecture, Server and Containers 25 Following a list of overview about the different tiers of J2EE architecture: 1) Client Tier : In JEE Architecture Components of Client Tier will run in the client devices / containers. Client Tier components are standalone or web based java applications, static and dynamic HTML pages, and applets. 2) Middle Tie r: I) Web Tier: In JEE the web tier components namely JSP and Servlets execute with the help of J2EE web server in a web container. II) Business Tier: In this tire integrate purely Business logic with Enterprise Java Beans (EJB) are the business tier comp onents that are executed within the EJB container using J2EE Application Server/web server. 3) EIS Tier : EIS (Enterprise Information Systems) tier follows operations related to application data that are stored in a database. EIS tier may also include ERP’s varois big operations or legacy systems. 2.4 JAVA EE SERVER A Java EE server is a server application that implements the Java EE platform APIs and provides the standard Java EE services for Design & developing Applications. Java EE servers are sometimes called application servers or web servers, because they allow you to serve application data to clients, same processing on web servers serve web pages to web browsers. Java EE servers host several application component types that correspond to the tiers in a multi -tiered application. The Java EE server provides services to these components in the form of a container.
Fig: 2.4 Java EE Communication Server: munotes.in
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Enterprise Java 26 2.4.1 Java EE Containers: Java EE containers are the interface between the component and the lowe r-level functionality of the application server provided by the platform to support that component and API . The functionality of the container is defined by the platform to provide more productivity, and is different for each component type. The server al lows the different component types to work together to provide the enhancement of functionality in an enterprise application.
Fig: 2.4.1 Java EE Containers 2.4.2 The Web Container: The web container is the interface between web components or API and the web server. A web component can be a JSP page, or a JavaServer Faces Facelets page, and servlet. The web container manages the processes of Request & Response in the component’s lifecycle , dispatches requests to application components, and provides i nterfaces to context data, such as information about the current request.
Fig: 2.4.2 TheWeb Container: munotes.in
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Java EE Architecture, Server and Containers 27 2.4.3 The Application Client Container: The application client container is the interface between Java EE applications and clients/browsers , which ar e special Java SE applications that use Java EE server components with more API’s , and the Java EE server. The application client container runs on the client machine, and is the gateway between the client application and the Java EE server components tha t the client/browsers uses.
Fig: 2.4.3 The Application Client Container. 2.4.4 The EJB Container: The EJB container is the interface between enterprise java beans, which provide the business logic in a Java EE application to manage data transportation in critical condition with the Java EE server. The EJB container runs on the Java EE server or web server and manages the execution of an application’s enterprise beans in Business Logic to Database and viceversa.
Fig: 2.4.4 The EJB Container. 2.5 JAVA EE CONTAINERS Containers easily manage their transaction and state management, multithreading, resource pooling, and other complex low -level details. The component -based and platform -independent. munotes.in
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Enterprise Java 28 Java EE architecture provides better service to write business logic that is organized into reusable components. Container Services: Containers are the interface between a component and the low -level platform -specific functionality that supports the component. Before a web, enterprise bean, or application client com ponent can be executed, it must be assembled into a Java EE module and deployed into its container. Key points of Container: In Java EE security models configure a web component or EJB so that system resources are accessed at client side/browsers only by authorized users. The Java EE transaction model provides relati onships among methods/functions that communicate a single transaction so that all methods/functions in single transaction are treated as a single unit. The Java EE can be remotely connecti vity model manages low -level communications between clients and EJB Following diagrams shows The deployment process installs Java EE application components in the Java EE containers as illustrated in Following Figure.
Figure 2.5 Java EE Server and Conta iner. Following are the list of Types of Container: 1) Enterprise JavaBeans (EJB) container: EJB containers can manage the execution of enterprise beans for Java EE applications/ web applications & services. EJB and their container run on the Java EE se rver/web server. munotes.in
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Java EE Architecture, Server and Containers 29 2) Web container: Here Web containers can manage the execution of JSP page and servlet components for Java EE applications. Web components and their containers run on the Java EE server/web server. 3) Application client container: Java E E Application client container can manage the execution of application client components. Java EE Application clients and their container run on the client/browser. 4) Applet container: Manages the execution of applets/java programs executed on client. Applet container consists of a web browser and Java Plug -in running on the client. 2.6 QUESTION 1 Explain in detail the container with types. 2 Explain Java EE Development Architecture. 3 Difference between Apache tomcat & Glassfish server. 4 Explain Java EE Deployment Architecture. 5 Explain Quality of Service layer in Java EE Deployment Architecture. 6 Define the web container. 7 Define the EJB container. 2.7 SUMMARY Web server is a computer where the web content is stored. Basically a web serve r is used to host the web sites . In java EE Containers are the interface between a component and the low -level, platform -specific functionality that supports the component. Java Enterprise Edition is a set of various specifications, for enterprise features such as dis tributed computing, Security, Powerful API’s and web services. 2.8 REFERENCE FOR FURTHER READING: 1. Java EE 6 Enterprise Architect Exam Guide ,Author: PaulAllen, Publisher: McGraw -Hill 2. The Complete Reference -Java Enterprise Edition (Black Book), Author:Herbert schildt. 3. Java EE 7 The Big Picture by - Dr.Danny Coward Publisher - Oracle press. 4. Advanced Java by -Balaguruswamy . 5. The Java Ee 7 Tutorial by -Ricardo Cervera -Navarro ***** munotes.in
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30 3 INTRODUCTION TO JAVA SERVLETS Unit Structure 3.1 Objectives 3.2 The Need for DynamicContent 3.2.1 Introduction 3.2.2 Dy namic content vs static content 3.2.3 Area s to implement Dynamic Content 3.3 Java Servlet Techno logy 3.3.1 Use of Servlet 3.3.2 CGI (Common Gateway Interface) 3.3.3 Servlet Technology 3.4 Why Servlets 3.5 What can Servlets do 3.6 Questions 3.7 Summary 3.8 Reference for further reading 3.1 OBJECTIVES 1) Java servlet provides server side coding technique. 2) Java servlet is used to de velop & design web applications in a web server. 3) Using servlet for students/professionals are able to originally design and develop & Deploy their application on server. 4) Servlet is a technology which is used to create a web application executed at server s ide. 5) Java servlet provides a powerful API for best Dynamic Web Programming. 3.2 THE NEED FOR DYNAMIC CONTENT 3.2.1 Introduction: Dynamic content refers to web content that changes based on the behaviour , preferences, and interests of the user. It refers to websites as well as e -mail content and is generated at the moment a user requests a page. Dynamic content is personalized and adapts based on the data you have about the user and on the access time, its goal being to deliver an engaging and satisfying onl ine experience for the visitor. munotes.in
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Introduction to Java Servlets 31 Dynamic content ( adaptive content) refers to web content that changes based on the behaviour , preferences, and interests of the user. It refers to websites as well as Email content and is generated at the moment a user requests a page. Dynamic content is personalized and adapts based on the data you have about the user and on the access time, its goal being to deliver an engaging and satisfying on line experience for the visitor. A server -side dynamic web page is a web page whose construction is controlled by an application server to process server -side scripts dynamically . In se rver-side scripting programming , an parameters determine how the assemb ly of every new web page proceeds as per user request, including the setting up of more client -side processing This content can be displayed in a variet y of different forms on the Web . The way it is usually presented is based on the type of website you are on. However, things like pictures, text, videos, newsletters, and other web forms are often great examples of this content being used. 3.2.2 Dynamic content vs static content : Static content has not changed on the internet. This is because it’s much easie r to implement than the dynam ic text alternatives on the Web . However, the downside is that static content is not personalized and thus it reduces the performance of the website. Dynamic content has various benefits as follows: Difference between Static and Dynamic Web Pages Sr.No Static Web Page Dynamic Web Page 1. In static web pages, Pages will remain same until someone changes it manually. In dynamic web pages, Content of pages are different for different visitors. 2. Static Web Pages are simple in terms of complexity. Dynamic web pages are complicated. 3. In static web pages, Information are change rarely. In dynamic web page, Information are change frequently. 4. Static Web Page takes less time for loading than dynamic web page. Dynamic web page takes more time for loading. 5. In Static Web Pages, database is not used. In dynamic web pages, database is used. 6. Static web pages are written in languages such as: HTML, JavaScript, CSS, etc. Dynamic web pages are written in languages such as: CGI, AJAX, ASP, ASP.NET, etc. 7. Static web pages does not contain any application program Dynamic web pages contains application program for different services. munotes.in
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Enterprise Java 32 8. Static web pages require less work and cost in designing them. Dynamic web pages require comparatively more work and cost in designing them. ● it makes for a more user -friendly experience on the web/Internet. ● it helps increase vital current data, latest information or instant info. ● Within page layout properly & accurate displays data. ● Once has been upload , live and active, you don’t need to tend to it anymore 3.2.3 Areas to implement Dynamic Content: 1) Newsletters and Emails: Newsletters and emails are probably the most basic and classic forms of dynamic content being presented as per requireme nt. Customized emails or customized form fields for specific users have been around on the web for a long time. Presenting your dynamic content this way is always a good choice because data is frequently changed. And some newsletter plugins will display its content/data as per updated content you re -purpose. 2) Landing Pages : A landing page is built specifically to target a cer tain thing or targeted audience . Whether it is a product or a service that has to be reached , the landing page acts as an informational doorway to what you are selling to an accurate customer. Take it further by presenting a landing page that uses dynamic content to display different information and items based on who is viewing it as per search & updated data. 3) Articles : Articles can be used to display dynamic content based on the device/platforms that is being used to read the article. This type of content can be displayed properly on any devic e and screen size or resolution . This is why your website should be mobile frie ndly and responsive web content . Giving the user viewable content no matter wher e they access it would be displayed in proper layout to any device or screen. 4) Forms and Purchases : As per every user requirement or organization operation perspective Different form and purchase fields or other information can be displayed, based on how the checkout is going to be on demand , who the user is, and what their interests are different users makes the entire experience much better for them. 5) Produ ct Pages : In E -commerce online stores will use product pages to cross -sell and match related items for the site user where the user chooses the products. munotes.in
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Introduction to Java Servlets 33 This is dynamic content at work using certain things to match up what we think or what the users need as per the user wants to see. Online store organization bounce offers like sales and coupons or other special recommendations as well. 6) Website Ads : Ads on websites, social media and on Google can use Digital marketing or Digital advertisement using dyna mic content technique. These ads display content on what users search and interests the website or Application. This makes ad interaction and click -throughs much more likely where users easily interact with. 3.3 Java Servlet Technology:
Servlet is a tech nology used to create a java web application ( placed at server side and generates a dynamic web page as per client request ). Servlet is a technology that is robust and scalable and secure because of the Java language. Before Servlet, CGI (Common Gateway I nterface) scripting language was common as a server -side programming language. There were many disadvantages of CGI. Some of these disadvantages are discussed below. Servlet API is a collection of various interfaces and classes in the Servlet API such as S ervlet, ServletResponse,ServletRequest GenericServlet, HttpServlet... etc. 3.3.1 Use of Servlet: Servlet technology can be described in many ways, As follows. ● Servlet is a technology which is used to create a java web application. ● Servlet is an API collect ion of various interfaces and classes. ● Servlet is an interface that must be implemented for creating any Servlet page. munotes.in
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Enterprise Java 34 ● Servlet is a class that extends the capabilities of the servers and responds to the incoming requests. It can respond to any requests. ● Servlet is a web component that is deployed on the server to create a dynamic web page.
Fig: 3.3 Communication of Java Servlet Technology. What is a web application? A web application is a server side application which is accessible from the web/web brows er. A web application is composed of web components like Servlet, Filter & JSP, etc. and other elements such as HTML, CSS, and JavaScript. The web components typically execute in Web Server and respond to the HTTP request. 3.3.2 CGI (Common Gateway Interfa ce): CGI technology enables the web server to call an external program and pass HTTP request information to the external program to process the request. For each & every request, it starts a new process or creates a new Thread for every request. i.e. Numbe r request coming to CGI , a number of newly processes or threads to create. CGI will get more load & responses are slow or its processing task may be heavy. The Common Gateway Interface (CGI) provides the middleware between WWW servers and external database s and information sources. The World Wide Web Consortium (W3C) defined the Common Gateway Interface (CGI) and also defined how a program interacts with a Hyper Text Transfer Protocol (HTTP) server. The Web server typically passes the form information to a small application program that processes the data and may send back a confirmation message. This process or convention for passing data back and forth between the server and the application is called the common gateway interface (CGI). Features of CGI: It is a very well defined and supported standard. munotes.in
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Introduction to Java Servlets 35 CGI scripts are generally written in either Perl, C, or maybe just a simple shell script. CGI is a technology that interfaces with HTML. CGI is the best method to create a counter because it is currently the quickest CGI standard is generally the most compatible with today’s browsers . Advantages of CGI: The advanced tasks are currently a lot easier to perform in CGI than in Java. It is always easier to use the code already written than to write your own. CGI sp ecifies that the programs can be written in any language, and on any platform, as long as they conform to the specification. CGI-based counters and CGI code to perform simple tasks are available in plenty.
Fig: 3.3.2 CGI (Common Gateway Interface) Commun ication flow. Disadvantages of CGI : There are many problems in CGI technology: 1. If the number of clients increases, it takes more time to send the response. 2. For each request, it starts a process, and the web server is limited to start processes. 3. It uses pla tform dependent languages e.g. C, C++, perl. 4. CGI facing Net work Traffic, because of heavy load. 5. Number request , Number of newly processes so CGI contain heavy load. munotes.in
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Enterprise Java 36 3.3.3 Servlet Technology & its Advantages:
Fig: 3.3.3 Servlet Technology Communication flow. As per comparison of Servlet & CGI there are many advan tages of Servlet over CGI. The web container/Servlet will create threads for handling the multiple requests to the Servlet. Threads have many benefits over the Processes happening in Network such as they share a common memory area of the server, are lightw eight, and cost of communication between the threads are low. Shortly after the Web began to be used for delivering services, service providers recognized the need for dynamic content. Applets, one of the earliest attempts toward this goal, focused on usi ng the client platform to deliver dynamic user experiences. At the same time, developers also investigated using the server platform for the same purpose. Initially, Common Gateway Interface (CGI) server -side scripts were the main technology used to genera te dynamic content. Although widely used, CGI scripting technology had many shortcomings, including platform dependence and lack of scalability. To address these limitations, Java Servlet technology was created as a portable way to provide dynamic, user-oriented content. The advantages of Servlet are as follows: 1. Better performance : No of process es is converted into threads so , because it creates a thread for each request, not process. 2. Portability: Servlet programs execute any platform because it uses Java l anguage. 3. Robust: JVM manages Servlet programs, so we don't need to worry about the memory leak, garbage collection, etc. 4. Secure: because it uses java language.
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Introduction to Java Servlets 37 Difference between Servlet and CGI Servlet CGI(Common Gateway Interface) Servlets are portable and efficient. CGI is not portable In Servlets, sharing data is possible. In CGI, sharing data is not possible. Servlets can directly communicate with the webserver. CGI cannot directly communicate with the webserver. Servlets are less expensive than CGI. CGI is more expensive than Servlets. Servlets can handle the cookies. CGI cannot handle the cookies. 3.4 WHY SERVLETS? Today’s Web applications trends it to creating dynamic web pages i.e the ones which have the capability to change the site conten ts according to the time/response or are able to generate the contents according to the request received by the client. If you like coding in Java, then you will be happy to know about Java. There also exists a way to generate dynamic web pages and that w ay is Java Servlet API. first understand the need for server -side extensions i.e why use servlet to develop dynamic applications. A servlet is a Java Programming language class that is used to extend the capabilities of servers that host applications acce ssed by means of a request -response programming model. Although servlets can respond to any type of request, they are commonly used to extend the applications hosted by web servers. It is also a web component that is deployed on the server to create a dyna mic web page.
Fig: How servlet Work. munotes.in
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Enterprise Java 38 In this figure you can see, a client sends a request to the server and the server generates the response, analyses it and sends the response to the client. Servlets are the Java programs that run on the Java -enabled w eb server or application server[Apache server, Glassfish server, etc….]. They are used to handle the request obta ined from the web server/Client , process the request, produce the response, then send a response back to the web server/web browser. Propertie s of Servlets are as follows: Servlets work on the server -side. Servlets are capable of handling complex requests obtained from the web server.
Fig: 3.4 Servlet Architecture
Execution of Servlets basically involves following basic steps: 1. The client s/browsers send the request to the web server. 2. The web server receives the request from clients. 3. The web server passes the request to the corresponding servlet container. 4. The servlet processes the request and generates the response in the form of output. 5. The servlet sends the response back to the web server. munotes.in
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Introduction to Java Servlets 39 6. The web server sends the response back to the client and the client browser displays it on the screen. 3.5 WHAT CAN SERVLETS DO? Introduction: Java Servlets are programs that run on a Web or Application server and act as a middle layer between a request coming from a Web browser or other HTTP client and databases or applications on the HTTP server. Using Servlets, you can collect input from users through web page forms, present records fro m a database or another source, and create web pages dynamically. Java Servlets often serve the same purpose as programs implemented using the Common Gateway Interface (CGI). But Servlets offer several advantages in comparison with the CGI: Performance is significantly better. Servlets execute within the address space of a Web server. It is not necessary to create a separate process to handle each client request. Servlets are platform -independent because they are written in Java. Java security manager on t he server enforces a set of restrictions to protect the resources on a server machine. So servlets are trusted. The full functionality of the Java class libraries is available to a servlet. It can communicate with applets, databases, or other software via the sockets and RMI mechanisms that you have seen already. Servlets Architecture The following diagram shows the position of Servlets in a Web Application.
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Enterprise Java 40 Servlets Tasks : Servlets per form the following major tasks Read the exp licit data sent by the clients (browsers). This includes an HTML form on a Web page or it could also come from an applet or a custom HTTP client program. Read the implicit HTTP request data sent by the clients (browsers). This includes cookies, media types and compression schemes the browser understands, and so forth. Process the data and generate the results. This process may require talking to a database, executing an RMI or CORBA call, invoking a Web service, or computing the response directly. Send the explicit data (i.e., the document) to the clients (browsers). This document can be sent in a variety of formats, including text (HTML or XML), binary (GIF images), Excel, etc. Send the implicit HTTP response to the clients (browsers). This includes telling the browsers or other clients what type of document is being returned (e.g., HTML), setting cookies and caching parameters, and other such tasks. 1) Dynamic website: Dynamic website is a collection of dynamic web pages whose content changes dynamically. I t accesses content from a database or Content Management System (CMS). Therefore, when you alter or update the content of the database, the content of the website is also altered or updated. Dynamic websites are those websites that changes the content or l ayout with every request to the webserver. These websites have the capability of producing different content for different visitors from the same source code file. There are two kinds of dynamic web pages i.e. client side scripting and server side scriptin g. The client -side web pages changes according to your activity on the web page. On the server -side, web pages are changed whenever a web page is loaded. Dynamic websites use client -side scripting or server -side scripting, or both to generate dynamic conte nt. Dynamic websites use client -side scripting or server -side scripting, or both to generate dynamic content. Client side scripting generates content at the client computer on the basis of user input. The web browser downloads the web page from the server and processes the code within the page to render information to the user. munotes.in
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Introduction to Java Servlets 41 In server side scripting, the software runs on the server and processing is completed in the server then plain pages are sent to the user.
2) The server -side extensions: In Java se rver side extensions i.e . servlet or JEE are nothing but the technologies that are used to create dynamic Web pages. In servlet Technology to provide the facility of dynamic Web pages, Web pages need a container or Web server. To complete this requirement, independent Web server providers offer some essentials solutions in the form of APIs(Application Programming Interface). 3) Handling Request & Response: In Servlet Technology for the purpose of communication to use HTTP protocol. The Hypertext Transfer P rotocol (HTTP) is an application -level protocol for distributed, collaborative and hypermedia information systems. HTTP Request & Response are the data communication protocol used to establish communication between client and server. HTTP is a stateless T CP/IP based communication protocol, which is used to send & receive data like image files, query results, HTML files etc on the World Wide Web (WWW) with the default port being TCP 80. It provides a standardized way for computers to communicate with eac h other in a network .
The Basic Characteristics of HTTP (HyperText Transfer Protocol): HTTP protocol allows web servers and browsers to exchange data over the web. HTTP a r equest response protocol. HTTPuses the reliable TCP connections by default on TCP port 80. HTTP is stateless means each request is considered as the new request. In other words, the server doesn't recognize the user by default. HttpServlet class provides s pecialized methods that handle the various types of HTTP requests. A servlet developer typically overrides one of these methods. These methods are doDelete( ), doGet( ), doHead( ), doOptions( ), doPost( ), doPut( ), and doTrace( ). However, the GET and POST requests are commonly used when handling form input. The doPost( ) method is overridden to process any HTTP POST requests that are sent to this servlet. It uses the getParameter( ) method of HttpServletRequest to obtain the selection that was made by the user. 4) Filtering Requests and Responses: In Servlet Technology to provide a filter object that can transform the header and content (or both) of a request or response. In the Servlet Filters objects differ from web components in that filters usually do not themselves create a response. Instead a filter object provides functionality that can be “attached” to any kind of web resource with servlet objects. In Servlet filter Object can perform following tasks: ● Filter object Query the request and act acco rdingly. ● Block the request -and-response pair from passing any further transaction. ● Filter objects can modify the request headers and data. You do this by providing a customized version of the request. munotes.in
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Introduction to Java Servlets 43 ● In Filter Modify the response headers and data. You do this by providing a customized version of the response. ● Filter Objects are Interact with various external resources. 5) Sharing Information: In servlet its mechanism is objects communicate in through a network. There are several ways they can do this. In Java Servlet class can use private helper objects (for example, JavaBeans components), Servlet class (beans) can share objects that are attributes of a public scope or private, they can use a database, and they can invoke other web resources. In servlet its mechanism is objects communicate in through a network. There are several ways they can do this. In Java Servlet class can use private helper objects (for example, JavaBeans components), Servlet class (beans) can share objects that are attributes of a public scope or private, they can use a database, and they can invoke other web resources. The Java Servlet technology mechanisms that can be allowed to access a component to invoke other web resources are described in Invoking Other Web Resources. 6) Accessing the Web Context: In The Servlet context in which web components execute is an object that implements the ServletContext interface. You retrieve the web context using the getServletContext method. The web context provides methods for accessing: ● Initialization parameters. ● Resources associated with the web context. ● Object -valued attributes. ● Logging capabilities. 3.6 QUESTIONS 1. Explain what is Dynamic Content? 2. Explain what is needed to be Design Dynamic Content. 3. Explain the features of Servl et. 4. Explain in detail Why Servlet is popular as compared to CGI. 5. Difference between Servlet Vs CGI. 6. Explain Use of Servlet in Web Application. 7. Define Servlet API. munotes.in
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Enterprise Java 44 8. Explain in brief What can servlet do? 9. Explain in detail Servlet Architectur e. 10. Define Request & Response Methodology. 3.7 SUMMARY A server -side dynamic web page is a web page whose construction is controlled by an application server to process server -side scri pts dynamically . In se rver-side scripting programming , parameters de termine how the assembly of every new web page proceeds as per user request, including the setting up of more client -side processing. Dynamic content is personalized and adapts based on the data you have about the user and on the access time, its goal bein g to deliver an engaging and satisfying online experience for the visitor. Servlet is a technology used to create a java web ap plication ( placed at server side and generates a dynamic web page as per client request ). Servlet is a technology that is robust and scalable and secure because of the Java language. Before Servlet, CGI (Common Gateway Interface) scripting language was common as a server -side programming language. There were many disadvantages of CGI. Some of these disadvantages are discussed below. The client -side web pages changes according to your activity on the web page. On the server -side, web pages are changed whenever a web page is loaded. Dynamic website is a collection of dynamic web pages whose content changes dynamically so we can design such a dynamic application using servlet. It accesses content from a database or Content Management System (CMS). 3.8 REFERENCE FOR FURTHER READING 1. The Complete Reference -Java Enterprise Edition (Black Book) , Author:Herbert schildt. 2. Java EE 7 The Big Picture by - Dr.Danny Coward Publisher - Oracle press. 3. Advanced Java by -Balaguruswamy . 4. The Java Ee 7 Tutorial by -Ricardo Cervera -Navarro. ***** munotes.in
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45 4 SERVLET API AND LIFECYCLE Unit Structure 4.1 Objectives 4.2 Java Servlet API 4.3 The Servlet Skeleton 4.4 The Servlet Life Cycle 4.5 A Simple Welcome Servlet Program 4.6 Questions 4.7 Summary 4.8 Reference for further reading 4.1 OBJECTIVES 1) Java Ser vlet Provides Server side Programming techniques. 2) Java Servlet Provides Flexible Architecture where we can communicate easily through a web server. 3) Java Servlet for implementation of communication between client & server. 4) Java Servlet Provides a mechanism i.e handles the request & response services. 5) Java Servlet provides a powerful API for Strong and Dynamic Web Programming. 6) Students/professionals are able to originally design and develop & deploy their application on server. 4.2 JAVA SERVLET API In Java S ervlet Containing API i.e the javax.servlet and javax.servlet.http packages represent interfaces and classes for servlet API Where to design java web applications. The javax.servlet package contains so many interfaces and classes that are used by the serv let or web container programming. The javax.servlet.http package contains interfaces and classes that are responsible for handling HTTP related Requests & Responses from client to server & viceversa. In Java EE Servlet interface provides common behavi or to all the servlets. Servlet interface defines methods that all servlets must implement for handling processes. munotes.in
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Enterprise Java 46 Servlet interface needs to be implemented for creating any servlet (either directly or indirectly) Without servlet interface servlet class wi ll not be generate. In the Javax.servlet package , the ServletRequest Interface is used to handle client requests to access a servlet. It provides th e information of a servlet like , parameter names, content type, content length and values. In the Javax.serv let package, the ServletResponse interface defines an object to help a Servlet in sending a response to the client/browser. It has various methods that help communicate a servlet to respond to the client requests. In the Javax.servlet package , the RequestD ispatcher interface provides the facility of dispatching the request to another resource , be it html, servlet or jsp. This interface can also be used to include the content of another resource. Following are the inte rfaces of javax.servlet package: There are many interfaces in the javax.servlet package. They are as follows: 1. Servlet Interface. 2. ServletRequest. 3. ServletResponse. 4. RequestDispatcher. 5. ServletConfig: 6. ServletContext 7. ServletRequestListener 8. ServletRequestAttributeListener 9. ServletContextListener 10. ervlet ContextAttributeListener Following are the List of Classes in javax.servlet package 1. GenericServlet. 2. ServletInputStream. 3. ServletOutputStream. munotes.in
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Servlet API and Lifecycle 47 4. ServletRequestWrapper. 5. ServletResponseWrapper. 6. ServletRequestEvent. 7. ServletContextEvent. 8. ServletRequestAttributeEve nt. 9. ServletContextAttributeEvent. 10. ServletException. 11. UnavailableException. Following are the List of Interface s in javax.servlet.http package: 1) HttpServletRequest. 2) HttpServletResponse. 3) HttpSession. 4) HttpSessionListener. 5) HttpSessionAttributeListener. 6) HttpSess ionBindingListener. 7) HttpSessionActivationListener. Following are the List of Classes in javax.servlet.http package : 1) HttpServlet. 2) Cookie. 3) HttpServletRequestWrapper 4) HttpServletResponseWrapper 5) HttpSessionEvent. 6) HttpSessionBindingEvent. 4.3 THE SERVLET SKELE TON Servlet development: a skeleton Servlet, Once you have set up your Servlet environment , the first step is generally to write a test Servlet using code such as the skeleton shown in this example. munotes.in
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Enterprise Java 48 To write a basic Servlet, you generally: overwrite HttpServlet; overwrite the doGet() and doPut(). In servlet there are two methods: doGet() and doPut(). These methods will be called in response to GET and POST requests from the user's web browser/client side. Unless you specifically need your web application to respond differently to the two types of request. Servlet code looks as follows: import java.io.*; impor t javax.servlet.*; import javax.servlet.http.*; public class BasicServlet extends HttpServlet { public void doGet(HttpServletRequest req, HttpServletResponse res) throws ServletException, IOException { res.setContentType("text/html"); PrintWri ter pw = res.getWriter(); // ... output page to pw... } public void doPost(HttpServletRequest req, HttpServletResponse res) throws ServletException, IOException { doGet(req, res); } } The above example doesn't actually output any HTML, but i t shows the basic anatomy of a servlet class. Class extends HttpServlet and must provide implementations of the two methods. These methods correspond to HTTP get() and post() methods respectively. Developers can generally make doPost() simply pass the re quest to doGet(). Servlets containing both types of requests essentially look the same. For example, parameters will be extracted from either a URL or POSTed data. munotes.in
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Servlet API and Lifecycle 49 4.4 THE SERVLET LIFE CYCLE In Java Servlet , The web container maintains the life cycle of a servlet instance/Object. Following are the Stages of life cycle of the servlet: 1. Servlet class is loaded. 2. Servlet instance is created. 3. init method is invoked. 4. service method is invoked. 5. destroy method is invoked. Fi g: 4.4 Stages of servlet life cycle . As displayed in the above diagram, there are three states of a servlet namely: new, ready and end. The servlet is in a new state if the servlet instance is created. After invoking the init() method, Servlet comes in the ready state. In the ready state, se rvlet performs all the tasks. When the web container invokes the destroy() method, it shifts to the end state. 1) Servlet class is loaded: In servlet while executing the servlet class first stage is i.e classloader is responsible for loading the servlet c lass into RAM. servlet class is loaded when the first request comes from the web container.
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Enterprise Java 50 2) Servlet instance is created: After loading the servlet class web container creates the instance of a servlet t class. The servlet instance/object is created only once in the servlet life cycle; the second time request is not created. 3) init method is invoked: The web container/web server calls the init() method only once after creating the servlet instance. Basically the init() method is used to initialize t he servlet. init() method is the content of the life cycle of the javax.servlet.Servlet interface. Syntax : public void init(ServletConfig config) 4) service method is invoked: The web container/web server calls the service method each time when a request for the servlet is received. If the servlet class or object is not initialized, again it follows the first three steps as described above then calls the service method. If the servlet is initialized, it calls the service method. Syntax: public void servi ce(ServletRequest reque st, ServletResponse response) 5) destroy method is invoked: The web container/web server calls the destroy method before removing the servlet instance from the RAM. destroy() method gives the servlet an opportunity to clean up any resource for example memory, thread etc. 4.5 SIMPLE WELCOME SERVLET PROGRAM There are 6 steps to create a servlet Program example. Following are These steps are required for writing the Servlet Programs. The servlet example can be created by three w ays: Implementing Servlet interface. Inheriting GenericServlet class. Inheriting HttpServlet class. The most used approach is by extending HttpServlet in the desired servlet file because it provides http request/response , specific methods such as doGet(), doPost(), doHead(). ❖ Steps to Create & Execute servlet Program: munotes.in
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Servlet API and Lifecycle 51 1) Create a directory structures: The directory structure defines where to put the different types of files so that the web container may get the information and respond to the client. The Sun Microsystem defines a unique standard to be followed by all the server vendors. Let's see the directory structure that must be followed to create the servlet.
As you can see, the servlet class file must be in the classes folder. The web.xml file must be under the WEB -INF folder. 2) Create a Servlet file: There are three ways to create the servlet 1. By implementing the Servlet interface 2. By inheriting the GenericServlet class 3. By inheriting the HttpServlet class The HttpServlet class is widely used to create t he servlet because it provides methods to handle http requests such as doGet(), doPost doHead() etc. In this servlet example we are going to create a servlet class that will be extended from HttpServlet class. In this example, we are inheriting the HttpSe rvlet class and providing the implementation of the doGet() method. Notice that get request is the default request munotes.in
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Enterprise Java 52 Create File : SampleServlet.java import javax.servlet.http.*; import javax.servlet.*; import java.io.*; public class SampleServlet ex tends HttpServlet//servlet class is extends from Httpservlet class. { public void doGet(HttpServletRequest request,HttpServletResponse response) throws ServletException,IOException { response.setContentType("text/html");//setting the content type PrintWriter pw=response.getWriter();//get the stream to write the data //writing html in the stream pw.println("
"); pw.println("Welcome to servlet"); pw.println(""); pw.close();//closing the stream } } 3) Compile th e servlet : For compiling the Servlet, a jar file is required to be loaded. Different Servers provide different jar files: Jar files Desired Server 1) servlet-api.jar Apache Tomcat 2) weblogic.jar Weblogic 3) javaee.jar Glassfish 4) javaee.jar JBoss Put the java file in any folder. After compiling the java file, paste the class file of servlet in WEB -INF/classes directory. munotes.in
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Servlet API and Lifecycle 53 4) Create the deployment descriptor (web.xml file) : The deployment descriptor is an xml file, from which Web Container gets the inf ormation about the servet to be invoked. The web container uses the Parser to get the information from the web.xml file. There are many xml parsers such as SAX, DOM and Pull. There are many elements in the web.xml file. Here are some necessary elements to run the simple servlet program. web.xml file umesh SampleServlet
umesh /welcome
Description of the content of web.xml file : There are too many elements in the web.xml file. Here is the illustration of some elements that are used in the above web.xml file. The elements are as follows: 1. represents the whole application. 2. is a sub element of and represents the servlet. 3. is a sub element of that represents the name of the servlet. 4. is a sub element of that represe nts the class of the servlet. 5. is a sub element of . It is used to map the servlet. 6. is a sub element of . This pattern is used at client side to invoke the servlet. munotes.in
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Enterprise Java 54 5) Start the Server and dep loy the project : To start Apache Tomcat server, double click on the startup.bat file under apache -tomcat/bin directory. ❖ One Time Configuration for Apache Tomcat Server You need to perform 2 tasks: 1. We have to set JAVA_HOME or JRE_HOME in the environment variable (It is required to start the server). 2. To Change the port number of tomcat (optional). It is required if another server is running on the same port (8080). 1) How to set JAVA_HOME in the environment variable : To start Apache Tomcat server JAVA_HOME an d JRE_HOME must be set in Environment variables. Right click on my computer/ThisPC -> Click on advanced tab then environment variables -> Click on the new tab of user variable -> Write JAVA_HOME in variable name and paste the path of jdk folder in variable value -> Then click on ok Go Computer properties:
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Servlet API and Lifecycle 55 Click on advanced system settings:
Click on the new tab of user variable or system variable whenever required: munotes.in
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Enterprise Java 56 JAVA_HOME in variable name and paste the path of jdk folder in variable value unti l bin directory:
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Servlet API and Lifecycle 57 Finally, the Apache server is started successfully. 2) How to change port number of apache tomcat : TO change port number is required if there is another server running on the same system with the same port number. Suppose you have in stalled oracle, you need to change the port number of apache tomcat because both have the default port number 8080. By manually we can change the port no. Open server.xml file in notepad. It is located inside the apache -tomcat/conf direct ory. TO Change the Connector port = 8080 and replace 8080 by any four digit number instead of 8080. E.g replace it by 9999 and save this file. 5) How to deploy the servlet project : Copy the project and paste it in the webapps folder under apache tomcat.
You can also crea te a war file, and paste it inside the webapps directory. To do so, you need to use a jar tool to create the war file. Go inside the project directory (before the WEB -INF), then write: projectfolder> jar cvf myproject.war Creating a war file has the advan tage that moving the project from one location to another takes less time. 6) How to access the servlet class: Now Open browser and write in the address bar http://hostname:portno/contextroot/urlpatternofservlet. For example: http://localhost:9999/demo/wel come munotes.in
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Enterprise Java 58
2) Example of Student Registration form in servlet: In this example, we have created the three pages. register.html Register.java web.xml 1) Student Register.html : In this web page, we have input from the user using text fields and Dropdown list. T he information entered by the user is forwarded to the Register servlet.
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Servlet API and Lifecycle 59
2) Register.java: This Java Servlet class File is designed to receive all the data entered by the user and store it into the database. Here, we are performing the database logic. impor t java.io.*; import java.sql.*; import javax.servlet.ServletException; import javax.servlet.http.*; public class Register extends HttpServlet { public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletExceptio n, IOException { response.setContentType("text/html"); PrintWriter out = response.getWriter(); String uname=request.getParameter("userName"); String upass=request.getParameter("userPass"); String uemail=request.getParameter("userEmail"); String uc=request.getParameter("userCountry"); PrintWriter out = response.getWriter(); out.println("
User name=" +uname + "
"); out.println("
User pass=" +upass+ "
"); out.println("
User email=" +uemail+ "
"); out.println("
User co untry=" +uc+ "
"); out.close(); } } 3) web.xml file : Web.xml is the configuration file, to provide information about the servlet. Register munotes.in
4.6 QUESTIONS 1. Define Servlet? 2. Explain in detail the servlet life cycle. 3. Explain API of Servlet. 4. Differentiate between servlet & CGI. munotes.in
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Servlet API and Lifecycle 61 5. Why use ser vlets? 6. Explain servlet interface. 7. Explain Role of servlet in web application. 8. Explain stages of executing servlet programs. 9. Explain javax.servlet package. 10. Explain javax.servlet.http package. 4.7 SUMMARY In java servlet technology is use d to create a web application (basically resides at server side and generates a dynamic web page as per request). Java Servlet technology is secure, robust and scalable because of the Java language features. Before Servlet, CGI (Common Gateway Interface) t his scripting language was used for server -side programming language. In the servlet API there are many interfaces and classes such as Servlet, GenericServlet, HttpServlet, ServletRequest, ServletResponse. 4.8 REFERENCE FOR FURTHER READING 1. The Complete Reference -Java Enterprise Edition (Black Book) , Author:Herbert schildt. 2. Java EE 7 The Big Picture by - Dr.Danny Coward Publisher - Oracle press. 3. Advanced Java by -Balaguruswamy . 4. The Java Ee 7 Tutorial by -Ricardo Cervera -Navarro.
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62 5 WORKING WITH SERVLETS Unit structure 5.1 Objectives 5.2 Annotations in Java 5.3 Getting Started with servlet 5.4 Using Annotations I nstead of Deployment Descriptor 5.5 Servlet Program 5.6 Questions 5.7 Summary 5.8 Reference for furt her reading 5.1 OBJECTIVES 1) Java Servlet Provides Server side Programming techniques. 2) In Java Servlet for implementation of XML file or Deployment Descriptor file. 3) We can use Annotation “ @webservlet” for there is no requirement for a Deployment Descriptor file i.e web.xml . 4) Java Servlet provides a powerful API for Strong and Dynamic Web Programming. 5) students/professionals are able to originally design and develop & Deploy their application on server. 5.2 JAVA ANNOTATIONS In java Annotations is a tag that represen ts the metadata(Data about Data) i.e. attached with class, interface, methods or fields to indicate some additional information which can be used by java compiler and JVM. Annotations in Java are used to provide additional information, so it is an alternat ive option for XML i.e web.xml file (Deployment Descriptor) and Java marker interfaces. Built -In Java Annotations : There are several built -in annotations in Java. Some annotations are applied to Java code and some to other annotations. Built -In Java Annota tions used in Java code : 1. @Override 2. @SuppressWarnings 3. @Deprecated munotes.in
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Working with Servlets 63 ● Let's Discuss with Built -In Annotations: 1) @Override : @Override annotation assures that the subclass method is overriding the parent class method. If it is not so, a compile time error occur s. Sometimes, we make silly mistakes such as spelling mistakes etc. So, it is better to mark @Override annotation that provides assurity that method is overridden. class Student { void learnSomething() { System.out.println("Learning something"); } } class Result extends Student { @Override void learnsomething() { System.out.println("Result ----”); }//should be override learnSomething } class TestStudent { public static void main(String args[]) { Student a=new Result(); a.learnSomethin g(); } } Output: Compile Time Error 2) @SuppressWarnings: @SuppressWarnings annotation: is used to suppress warnings issued by the compiler. import java.util.*; munotes.in
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Enterprise Java 64 class Employee { @SuppressWarnings("unchecked") public static void main(String args[] ) { ArrayList emplist=new ArrayList(); list.add("Umesh"); list.add("Datta"); list.add("Monu"); for(Object obj1:emplist) System.out.println(obj1); } } At Compile Time: Now no warning at compile time. If you remove the @SuppressWarnings("unch ecked") annotation, it will show a warning at compile time because we are using a non -generic collection. 3) @Deprecated : @Deprecated annotation marks that this method is deprecated so the compiler prints a warning. It informs users that it may be removed in the future versions. So, it is better not to use such methods. class A { void mfun(){System.out.println("hello m"); } @Deprecated void nfun() { System.out.println("hello n"); } } class TestAnnotation3 { public static void main(String args[]) { A a=new A(); munotes.in
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Working with Servlets 65 a.nfun(); } } At Compile Time: Note: Test.java uses or overrides a deprecated API. 5.3 GETTING STARTED WITH SERVLET Servlet is the key component that forms a typical Java EE application, beside JSP, EJB, XML and other related techno logies. A Java EE application can be packaged/Archived in a WAR file (Web ARchive) in order to be deployed on a web server/Application server. A web server that can run Java servlets is called a servlet container. The most popular and widely used servlet containers are - Apache Tomcat, JBoss, Glassfish etc. In Java EE servlet is a simple Java class that extends either: ● javax.servlet.GenericServletclass for generic client -server protocol. ● javax.servlet.http.HttpServlet class for HTTP protocol communicatio n purpose. Java servlet is mostly used for handling HTTP requests & response , by overriding the HttpServlet’s doGet(), doPost() methods to handle GET and POST methods to response, respectively. The servlet container supplies an HttpServletRequest object and HttpServletResponse object for dealing with the handling request and response . Servlet is usually used in conjunction with JSP for generating dynamic content based on client’s requests. Annotations in servlet: In Servlet Annotation represents the met adata. It will be prefix “@” symbol in Servlet with Annotation, When you use annotation (@WebServlet), deployment descriptor (web.xml file) is not required. If we want to execute a servlet using annotations you should have a tomcat7 and above web server to execute the servlet. As it will not run in the previous versions of tomcat. @WebServlet annotation is used to map the servlet with the specified name(URL). In Java Servlet uses the deployment descriptor (web.xml file) for deploying/hosting your applicati on into a web server. In java Servlet API 3.0 has introduced a new package called “ javax.servlet.annotation ” . It provides annotation types which can be used for annotating a servlet class. munotes.in
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Enterprise Java 66 If you use annotation, then the deployment descriptor (web.xml) is not required. But you should use tomcat7 or any latest version of tomcat. Annotations can replace equivalent XML file configuration in the web deployment descriptor file (web.xml) such as servlet declaration,servlet class,servlet url and servlet mappin g. Servlet containers will process the annotated classes at deployment time. Following are The list of annotation types introduced in Servlet 3.0 .: Sr. No. Annotation & Description 1 @WebServlet: To declare a servlet. 2 @WebInitParam: To specify an ini tialization parameter. 3 @WebFilter: To declare a servlet filter. 4 @WebListener : To declare a WebListener 5 @HandlesTypes: To declare the class types that a ServletContainerInitializer can handle. 6 @HttpConstraint: This annotation is used within the ServletSecurity annotation to represent the security constraints to be applied to all HTTP protocol methods for which a corresponding HttpMethodConstraint element does NOT occur within the ServletSecurity annotation. 7 @HttpMethodConstraint: This annotation is used within the ServletSecurity annotation to represent security constraints on specific HTTP protocol messages. 8 @MultipartConfig: Annotation that may be specified on a Servlet class, indicating that instances of the Servlet expect requests that conform to the multipart/form-data MIME type. 9 @ServletSecurity: This annotation is used on a Servlet implementation class to specify security constraints to be enforced by a Servlet container on HTTP protocol message.
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Working with Servlets 67 5.4 USING ANNOTATIONS INSTEAD OF DEPLOYMENT DESCRIPTOR 1) A Program of simple servlet by annotation without web.xml file (Deployment Descriptor): SimpleExample.java : import java.io.IOException; import java.io.PrintWriter; import javax.servlet.ServletException; import javax .servlet.annotation.WebServlet; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; @WebServlet("/SimpleExample") //Annotations public class SimpleExample extends Http Servlet { protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { response.setContentType("text/html"); PrintWriter out=response.getWriter(); out.print("
Enterprise Java 68 5.5 -SERVLET PROGRAM 2) A Program Design Student Registration process using servlet by annotation without web.xml file: TO Designing a servlet we have to create the three pages. 1. register.html 2. Register.java 1) Student Register.html: In this page, we have input from the user using text fields and combobox. The information entered by the user is forwarded to the Register servlet.
2) Register.java: This servlet class receives all the data entered by the user and stores it into the database. Here, we are performing the database logic. But you may separate it, which will be better for the web application. import java.io.*; import javax.servlet.http.*; import java.io.IOException; munotes.in
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Working with Servlets 69 import java.io.PrintWriter; import javax.servlet.ServletException; import javax.servlet.annotation.WebServlet; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; @WebSer vlet("/register") public class Register extends HttpServlet { public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { response.setContentType("text/html"); PrintWriter out = response.g etWriter(); String uname=request.getParameter("userName"); String upass=request.getParameter("userPass"); String uemail=request.getParameter("userEmail"); String uc=request.getParameter("userCountry"); PrintWriter out = response.getWriter(); out.println("
Enterprise Java 70 2) Output Scre en : Register.java :
5.6 QUESTIONS 1. Explain what is the use of “annotation” in Java. 2. Explain in detail @WebServlet annotation in java. 3. What is needed to use annotations except web.xml. 4. Explain @override annotations in java. 5. Explain @Depreca ted annotations in java. 6. Explain in detail the flow of executing annotations. 7. List of annotations in servlet 3.0 8. Write a servlet program for calculate simple & compound interest. 9. Write a servlet program for Display entered Username . 5.7 SUMMAR Y Java Annotation is a tag that represents the metadata i.e. attached with class, interface, methods or fields to indicate some additional information which can be used by java compiler and JVM. Annotations in Java are used to provide additional informatio n, so it is an alternative option for XML and Java marker interfaces. The servlet container supplies an HttpServletRequest object and HttpServletResponse object for dealing with the handling request and response . In Servlet Annotation represents the metad ata. It will be prefix “@” symbol in Servlet with Annotation, When you use annotation (@WebServlet), deployment descriptor (web.xml file) is not required. If we want to execute a servlet using annotations you should have a tomcat7 and above web server to execute the servlet. munotes.in
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Working with Servlets 71 5.8 REFERENCE FOR FURTHER READING 1. The Complete Reference -Java E nterprise Edition (Black Book) , Author:Herbert schildt. 2. Java EE 7 The Big Picture by - Dr. Danny Coward Publisher - Oracle press. 3. Advanced Java by -Balaguruswamy .
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72 6 WORKING WITH DATABASE S Unit structure 6.1 Objectives 6.2 What Is JDBC 6.3 JDBC Architecture 6.3.1 Two -tier Architecture 6.3.2 Three -tier Architecture 6.4 Accessing Database 6.5 The Servlet GUI and Database Example 6.6 Questions 6.7 Summary 6.8 Refer ence for further reading 6.1 OBJECTIVES 1) JDBC is useful for A DataSource object that is used to establish connections . 2) Using Objects of JDBC classes & interfaces to be executing SQL Statements . 3) Extracting metadata of a data source via JDBC driver. 4) JDBC Dr iver Manager can also be used to establish a connection between Java & Database . 5) Using JDBC API we can Design & Develop GUI Web Application in Java. 6.2 WHAT IS JDBC JDBC stands for Java Database Connectivity JDBC basically used in java programming for c reate/implement connection betw een java application & database . Java API provides JDBC Driver is a software component / module that enables java applications to connect with the database. JDBC is a Java API to connect and execute the SQL query with the da tabase. JDBC API uses JDBC drivers to connect with the database and java application. Following are the types of JDBC drivers: 1. JDBC -ODBC Bridge Driver, 2. Native Driver, 3. Network Protocol Driver, and munotes.in
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Working with Databases 73 4. Thin Driver : In a java application we can use JDBC API to a ccess tabular/structured data stored in any relational database. With the help of JDBC API, we can save, update, delete and fet ch data from the database. JDBC like Open Database Connectivity (ODBC) provided by Microsoft.
Fig: 6.2 JDBC Connection The java .sql package contains classes and interfaces for JDBC API. How to import java.sql package in to java application E.g Import java.sql.*; Following are the list of popular interfaces of JDBC API : 1. Driver interface: In JDBC API the JDBC Driver interfac e provides powerful implementations of the abstract classes provided by the JDBC API for connection . JDBC driver must provide implementations of the java.sql. CallableStatement, PreparedStatement, Connection, Statement, ResultSet. 2. Connection interface: In JDBC API a Connection interface is the session between a Java application and database. The Connection interface is a factory of PreparedStatement, Statement, and DatabaseMetaData , that means objects of Connection can be used to get the object of Statem ent and DatabaseMetaData. Commonly used methods of Connection interface: A) public Statement createStatement(): In Java creates a statement object that can be used to execute SQL queries. munotes.in
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Enterprise Java 74 B) public Statement createStatement(int resultSetType,int resultS etConcurrency): Creates a Statement object that will generate ResultSet objects with the given type. C) public void close(): closes the connection and Releases a JDBC resources immediately. 1. Statement interface: The Statement interface provides methods to execute queries with the database. The statement interface is a factory of ResultSet i.e. it provides a factory method to get the object of ResultSet. Following are the important methods of Statement interface: A) public ResultSet executeQuery(String s ql): In Java is used to execute SELECT query. It returns the object of ResultSet when executing the query. B) public int executeUpdate(String sql): In Java is used to execute specified query, it may be create, drop, insert, update, delete. C) public boo lean execute(String sql): is used to execute queries that may return multiple results from a database. 1. PreparedStatement interface: The PreparedStatement interface is a subinterface of Statement. It is used to execute parameterized queries. example of para meterized query: String sql="insert into emp values(?,?,?)"; In the above example , we are passing parameters (?) for the values. Its value will be set by calling the setter methods of PreparedStatement. Why use PreparedStatement?: ● Improves performance: The performance of the application will be faster if you use PreparedStatement interface because the query is compiled only once. Methods of PreparedStatement interface. munotes.in
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Working with Databases 75 Following are the important methods of PreparedStatement interface are given below: Method Description public void setInt(int paramIndex, int value) In This method sets the integer value to the given parameter index. public void setString(int paramIndex, String value) In This method sets the String value to the given parameter index. public void setFloat(int paramIndex, float value) In This method sets the float value to the given parameter index. public void setDouble(int paramIndex, double value) In This method sets the double value to the given parameter index. public int executeUpdate() In This method executes the query. It is used for create, drop, insert, update, delete etc. public ResultSet executeQuery() In This method executes the select query. It returns an instance of ResultSet. 2. CallableStatement interface: In JDBC API Call ableStatement interface is used to call the stored procedures and functions. We can have business logic on the database by the use of stored procedures and functions that will make the performance better because these are precompiled. Suppose you need to g et the age of the employee based on the date of birth, you may create a function that receives date as the input and returns age of the employee as the output. Following are the differences between stored procedures and functions: Procedure Function is used to perform business logic. is used to perform calculations. must not have the return type. must have the return type. may return 0 or more values. may return only one value. We can call functions from the procedure. Procedure cannot be called from function. Procedure supports input and output parameters. Function supports only input parameters. Exception handling using try/catch block can be used in stored procedures. Exception handling using try/catch can't be used in user defined functions. munotes.in
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Enterprise Java 76 3. Resul tSet interface: The object of ResultSet maintains a cursor pointing to a row of a table. Initially, the cursor points to the first row. But we can make this object to move forward and backward direction by passing either TYPE_SCROLL_INSENSITIVE or TYPE_SCR OLL_SENSITIVE in createStatement(int,int) method as well as we can make this object as updatable by: Following are the Commonly used methods of ResultSet interface: Methods Description 1) public boolean next(): This method is used to move the cursor to the one row next from the current position. 2)public boolean previous(): This method is used to move the cursor to the one row previous from the current position. 3) public boolean first(): This method is used to move the cursor to the first row in the result set object. 4) public boolean last(): This method is used to move the cursor to the last row in the result set object. 5) public boolean absolute(int row): This method is used to move the cursor to the specified row number in the ResultSet object. 6) public boolean relative(int row): This method is used to move the cursor to the relative row number in the ResultSet object, it may be positive or negative. 7) public int getInt(int columnIndex): This method is used to return the data of specified column index of the current row as int. 8) public int getInt(String columnName): This method is used to return the data of the specified column name of the current row as int. munotes.in
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Working with Databases 77 9) public String getString(int columnIndex): This method is used to return the data of the specified column index of the current row as String. 10) public String getString(String columnName): This method is used to return the data of the specified column name of the current row as String Following are the a popular classes of JDBC API : DriverManager class: In JDBC API the DriverManager class acts as an interface between user and drivers for implementing bridge between Java Application & Database . It keeps track of the drivers that are available and handles establishing a connection b etween a database and the driver. Following are the methods of DriverManager class: Method Description 1) public static void registerDriver(Driver driver): This method is used to register the given driver with DriverManager. 2) public static void deregisterDriver(Driver driver): This method is used to deregister the given driver (drop the driver from the list) with DriverManager. 3) public static Connection getConnection(String url): This method is used to establish the connection with the specified url. 4) public static Connection getConnection(String url, String userName, String password): This method is used to establish the connection with the specified url, username and password. 6.3 JDBC ARCHITECTURE The JDBC API supports both two -tier and three -tier architecture of sql processing models for database access data .
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Enterprise Java 78 6.3.1 Two -tier Architecture: In the JDBC two -tier architecture model, a Java applet or application talks directly to the data source. This requires a JDBC driver that can communicate with the particular data source/database being accessed. A client sends a request to execute the database or other data source, and the results of those statements are sent back to the user. The data source may be located on another machine to which th e user is connected via a network. This is referred to as a client/server configuration where they can communicate to each other .
Figure 1: 6.3.1 Two -tier Architecture for Data Access. 6.3.2 Three -tier Architecture: In Java JDBC is a three -tier archite cture model, commands are sent to a "middle tier" of services, which then sends the commands to the data source/database. The data source /database processes the commands and sends the results back to the middle tier, which then sends them to the user. In this three -tier model is very attractive because the middle tier makes it possible to maintain control over access and the kinds of updates that can be made to corporate data. One more advantage is that it simplifies the deployment of java bapplications. Three -tier architecture can provide performance advantages.
Figure 2: 6.3.2 Three -tier Architecture for Data Access. munotes.in
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Working with Databases 79 The JDBC API is being used more and more in the middle tier of a three - tier architecture. In JDBC various features that make JDBC a serve r technology are its support for connection pooling, distributed transactions. The JDBC API is also what allows access to a data source/database from a Java middle tier. 6.4 ACCESSING DATABASE A) Insert Records in Database(MySql): In this example how to i nsert records in a table using the JDBC application. Required Steps: The following are the steps to create a new Da tabase using JDBC application: 1. Import the packages : import keywords specify that you include the packages containing the JDBC classes nee ded for database programming. Most often, using import java.sql.* will suffice. 2. Register the JDBC driver : Requires that you initialize a driver so you can open a communications channel with the database. 3. Open a connection : Open() method used in the DriverManager.getConnection() method to create and open a Connection object, which represents a physical connection with a database . 1. Execute a query : execute() method used for an object of type Statement for building and submitting an SQL statement to insert records into a desired table. 2. Cleaning up the environment with resources automatically closes the resources. Sample Code import java.sql.Connection; import java.sql.DriverManager; import java.sql.SQLException; import java.sql.Statement; public class InsertData { String DB_URL = "jdbc:mysql://localhost/Umesh"; String USER = "guest"; String PASS = "guest123"; public static void main(String[] args) munotes.in
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Enterprise Java 80 { // Open a connection Connection conn = DriverManager.getConnection(DB_URL, USER, PASS); Statemen t stmt = conn.createStatement(); Try { // Execute a query System.out.println("Inserting records into the table..."); String sql = "insert into UserRegistration VALUES (100, 'Umesh', 'Waghmare', 30)"; stmt.executeUpdate(sql); sql = "inse rt into UserRegistration VALUES (101, 'Shreya', 'Patil', 25)"; stmt.executeUpdate(sql); sql = "insert into UserRegistration VALUES (102,’Nilima’, 'Adagale', 30)"; stmt.executeUpdate(sql); sql = "insert into UserRegistration VALUES(103, 'Mimu', 'Mittal', 25)"; stmt.executeUpdate(sql); System.out.println("Inserted records into the table..."); } catch (SQLException e) { e.printStackTrace(); } } } Now let us compile the above example as follows − C:\>javac InsertData.java C:\> When you run InsertDat a, it produces the following result − C:\>java InsertData Inserting records into the table... Inserted records into the table... C:\> munotes.in
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Working with Databases 81 B) Retrieve/Access Records from Database(MySql): In java JDBC API specify to select/ fetch records from a table using JD BC Driver/application. Following are the Required Steps: The following steps are required to create a new Database using JDBC application: 1. Import the packages : import keywords that include the packages containing the JDBC classes needed for database rela ted programming. E.g import java.sql.*; 2. Open a connection : Open() method used in the DriverManager.getConnection() method to create a Connection object, which represents a physical connection with a database . 3. Execute a query : executeQuery() method used as an object of type Statement for building and submitting an SQL statement to select (i.e. fetch/access ) records from a table. 4. Extract Data : SQL query is executed successfully , you can fetch/access records from the table. 5. Clean up the environment : try with resources automatically. Sample Code import java.sql.Connection; import java.sql.DriverManager; import java.sql.ResultSet; import java.sql.SQLException; import java.sql.Statement; public class AccessData { String DB_URL = "jdbc:mysql://localhost/ume sh"; String USER = "guest"; String PASS = "guest123"; String QUERY = "SELECT id, first, last, age FROM Registration"; public static void main(String[] args) { // Open a connection Connection conn = DriverManager.getConnection(DB_URL, USER, PASS); Stateme nt stmt = conn.createStatement(); munotes.in
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Enterprise Java 82 ResultSet rs = stmt.executeQuery(QUERY); try { while(rs.next()) //Display values System.out.print("ID: " + rs.getInt("id")); System.out.print(", Age: " + rs.getInt("age")); System.out.println(", Last: " + rs. getString("last")); } } catch (SQLException e) { e.printStackTrace(); } } } Execute example as follows : C:\>javac AccessData.java C:\> When you run AccessData, i t produces the following result: C:\>java AccessData ID: 100, Age: 30, First: Umesh, Last: Waghmare ID: 101, Age: 25, First: Shreya, Last: Patil ID: 102, Age: 30, First: Nilima, Last: Adagale ID: 103, Age: 25, First: Mimu, Last: Mittal 6.5 THE SERVLET GUI AND DATABASE EXAMPLE: To start with basic concept, let us create a simple table and create few records in that table as follows − Create Table To create the Employees table in TEST database, use the following steps – Step 1 : Open a Command Prompt and change to the installation directory as follows − C:\> munotes.in
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Working with Databases 83 C:\>cd Program Files \MySQL \bin C:\Program Files \MySQL \bin> Step 2 : Login to database as follows C:\Program Files \MySQL \bin>mysql -u root -p Enter password: ******** mysql> Step 3 : Create the table Student in teststudent database as follows − mysql> use teststudent; mysql> create table Student ( id int not null, age int not null, first varchar (255), last varchar (255) ); Query OK, 0 rows affected (0.08 sec) mysql> Create Data Records Finally you create few records in Student table as follows − mysql> INSERT INTO Student VALUES (100, 30, 'Umesh', 'Waghmare'); Query OK, 1 row affected (0.05 sec) mysql> INSERT INTO Student VALUES (101, 25, 'Shreya', 'Patil'); Query OK, 1 row affected (0.00 sec)
mysql> INSERT INTO Student VALUES (102, 30, 'Nilima', 'Adagale'); Query OK, 1 row affected (0.00 sec) mysql> INSERT INTO Student VALUES (103, 28, 'Mimu', 'Mittal'); Query OK, 1 row affected (0.00 sec) mysql> Accessing a Database Here is an example which shows how to access teststudent database using Servlet. // Loading required libraries munotes.in
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Enterprise Java 84 import java.io.*; import java.util.*; import javax.servlet.*; import javax.servlet.http.*; import java.sql.*; public class DatabaseAccess extends HttpServlet { public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { // JDBC driver name and database URL String JDBC_DRIVER = "com.mysql.jdbc.Driver"; String DB_URL="jdbc:mysql://localhost/teststudent"; // Database credentials String USER = "root"; String PASS = "root"; // Set response content type response.setConten tType("text/html"); PrintWriter out = response.getWriter(); String title = "Database Result"; out.println( " \n" + "
Working with Databases 85 sql = "SELECT id, first, last, age FROM Student"; ResultSet rs = stmt.executeQuery(sql); // Extract data from result set while(rs.next()) { //Retrieve by column name int id = rs.getInt("id"); int age = rs.getInt("age"); String first = rs.getString("first"); String last = rs.getS tring("last"); //Display values out.println("ID: " + id + " "); out.println(", Age: " + age + " "); out.println(", First: " + first + " "); out.println(", Last: " + last + " "); } out.println(""); // Clean -up environment rs.close( ); stmt.close(); conn.close(); } catch(Exception e) { //Handle errors for Class.forName e.printStackTrace(); } } } Now let us compile above servlet and create following entries in web.xml .... DatabaseAccess DatabaseAccess munotes.in
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Enterprise Java 86 DatabaseAccess /DatabaseAccess
Now call this servlet using URL http://localhost:8080/DatabaseAccess which would display following response − Database Result : ID: 100, Age: 30, First: Umesh, Last: Waghmare ID: 101, Age: 25, First: Shreya, Last: Patil ID: 102, Age: 30, First: Nilima, Last: Adagale ID: 103, Age: 25, First: Mimu, Last: Mittal Example of Fetching Result for the given country : Here, you will learn how to fetch results for the given country. I am assuming that there is a table as given below: CREATE TABLE `registeruser` ( `uname` varchar(50) NOT NULL, `upass` varchar(45) DEFAULT NULL, `email` varchar (45) DEFAULT NULL, `country` varchar(45) DEFAULT NULL ); We are assuming there are many records in this table. In this example, we are getting the data from the database in servlet and Display on screen. In this example, we have create three files : 1. index.html 2. Search.java 3. web.xml 1) index.html : This page gets rollno from the user and forwards this data to servlet which is responsible to show the records based on the given country.
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2) Search.java : This is the servlet file which gets the input from the user and maps this data with the database and prints the record for the match ed data. In this page, we are displaying the column name of the database along with data, so we are using the ResultSetMetaData interface. import java.io.*; import java.sql.*; import javax.servlet.ServletException; import javax.servlet.http.*; public class Search extends HttpServlet { public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { response.setContentType("text/html"); PrintWriter out = response.getWriter(); String country =request.getParameter("country"); try{ Class.forName("com.mysql.jdbc.Driver"); Connection con=DriverManager.getConnection( "jdbc:mysql://localhost:3306/teststudent","root","root"); //here teststudent is database name, root is username an d password Statement stmt=con.createStatement(); ResultSet rs=stmt.executeQuery("select * from registeruser where country like +country+"); while(rs.next()) System.out.println(rs.getString(1)+" "+rs.getString(2)+" "+rs.getString(3)); con.close( ); } catch(Exception e) { munotes.in
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Enterprise Java 88 System.out.println(e); } } } 3) web.xml file This is the configuration file which provides information of the servlet to the container. Search Search< /servlet -class>
Search /servlet/Search
Output: 1) Input Screen
2) Output Screen :
6.7 SUMMARY JDBC is basically used in java programming for creating/implementing connections betwee n java applications & databases . In Java API JDBC Driver is a software component that enables java applications to connect with the database. JDBC is a Java API to conne ct and execute the SQL munotes.in
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Working with Databases 89 query with the database. JDBC is a part of JavaSE (Java Standard Edition). JDBC API uses JDBC drivers to connect with the database. 6.6 QUESTIONS 1 What is the use of JDBC? 2 Explain Architecture of JDBC. 3 Explain Two Tier Architec ture. 4 Explain types of JDBC drivers. 5 Explain Three Tier Architecture. 6 Discuss steps to connect java to a database. 7 Design a Employee registration (HTML form) insert records in the EmployeeDetails table and display all records. 8 Design Result (HTML form) and a servlet program for calculating student results with grades and display on browser. 6.8 REFERENCE FOR FURTHER READING 1. The Complete Reference -Java Enterprise Editio n (Black Book) , Author:Herbert schildt. 2. Java EE 7 The Big Picture by - Dr.Danny Coward Publisher - Oracle press. 3. Advanced Java by -Balaguruswamy .
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90 UNIT II 7 REQUEST DISPATCHER Unit Structure 7.0 Objectives 7.1 RequestDispatcher interface 7.2 Request Methods Dispatcher 7.3 Request Sender’s Request 7.4 Summary 7.5 References 7.6 Questions 7.0 OBJECTIVES The servlet container forms a RequestDis patcher object, which is used as a cover around a server resource located in a particular path or named. This link is intended for wrapping servlets, but the servlet container can create RequestDispatcher items to wrap any type of app. 7.1 REQUESTDISPATCHE R INTERFACE • A RequestDispatcher is an extremely important Java class that allows you to "include" content in a request / response or to "forward" a request / response to a resource. As a typical example, a servlet can use a RequestDispatcher to include or forward a request / response to a JSP. • A RequestDispatcher object can forward a client's request to a resource or include the resource itself in the response to the client. A resource can be another servlet, an HTML file or a JSP file, and so on. • You can a lso think of a RequestDispatcher object as a container for the resource located on a given path given as an argument to the getRequestDispatcher method. • To construct a RequestDispatcher object, you can use the ServletRequest.getRequestDispatcher () method or the ServletContext.getRequestDispatcher () method. They both do the same thing, but impose slightly different constraints on the path of the topic. For the former, it looks for the resource in the same web application that the invocation servlet belongs to, and the path name specified can be relative to the invocation servlet. For the latter, the path name must start with '/' and is interpreted in relation to the root of the web application. munotes.in
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Request Dispatcher 91 7.2 METHODS OF THE REQUESTDISPATCHER INTERFACE public void forw ard (ServletRequest request, ServletResponse response) throws ServletException, java.io.IOException: Forwards a request for a servlet to another resource (servlet, JSP file, or HTML file) on the server. public void include (ServletRequest request, Servlet Response response) throws ServletException, java.io.IOException: Include the content of a resource (servlet, JSP page, or HTML file) in the response.
How to get the RequestDispatcher object : • The getRequestDispatcher () method of the ServletRequest inte rface returns the RequestDispatcher object. How to get a RequestDispatcher object : • RequestDispatcher rs = request.getRequestDispatcher ("hello.html"); rs.forward (request, response); munotes.in
7.3 REQUEST THE SENDER'S REQUEST • In this example, we are validating the password entered by the user. If the password is a servlet, it will forward the request to the WelcomeServlet; otherwise it will display an error messag e: sorry, wrong username or password! In this example, we have created the following files: index.html file: to obtain information about the user. Access file.java: a servlet class to process the response. If the password is admin123, it will send the requ est to the welcome servlet. WelcomeServlet.java file: a servlet class to display the welcome message. web.xml file: a deployment descriptor file that contains servlet information.
index.html :
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Request Dispatcher 93 Password:
Validate.java : import java.io. *; import javax.servlet. *; import javax.servlet.http. *; Validate public class extend s HttpServlet { protected void doPost (HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { response.setContentType ("text / html; character set = UTF -8"); PrintWriter out = response.getWriter (); to deal { String name = request.getParameter ("user"); Password string = request.getParameter ("pass"); if (password.equal ("admin123")) { RequestDispatcher rd = request.getRequestDispatcher ("Welcome"); rd.forward (request, response); } the rest { out.printl n (" You entered an incorrect password "); RequestDispatcher rd = request.getRequestDispatcher ("index.html"); rd.include (request, response); } } Long last { out.close (); } } } Welcome.java : import java.io. *; import javax.servlet. *; import javax.servlet.http. *; The public class welcome extends HttpServlet munotes.in
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Enterprise Java 94 { protected void doPost (HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { response.setContentType ("text / html; character set = UTF -8"); PrintWriter out = response.getWriter (); to deal { out.println ("
Welcome user
"); } Long last { out.close (); }}} 7.4 SUMMARY The RequestDispatcher interface provides the facility of dispatching the reque st to another resource it may be html, servlet or jsp. This interface can also be used to include the content of another resource also. It is one of the ways of servlet collaboration. 7.5 REFERENCES https://www.javatpoint.com/java -tutorial https://www.tutorialspoint.com/java/index.htm https://www.geeksforgeeks.org/java/ https://www.oracle.com/in/java/technologies/java -ee-glance.html https://developers.redhat.com/topics/enterprise -java https://www.javacodegeeks.com/enterprise -java-tutorials 7.6 QUESTIONS 1. Explain the RequestDispatcher interface with its methods and diagram. 2. How to get the RequestDispatcher ob ject with syntax. 3. Provide an example to validate the password entered by the user. ***** munotes.in
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95 8 COOKIES Unit Structure 8.1 Introduction 8.1.1 Types of cookies 8.1.2 Where are cookies used? 8.1.3 Servlet cookie methods 8.2. Cookie settings with Servlet 8.3. Where are cookies used? 8.3.1 Applications 8.4 Where are cookies placed? 8.5 Simple example of a servlet cookie 8.6 Summary 8.7 References 8.8 Questions 8.1 INTRODUCTION Cookies are text files stored on the customer's computer and are saved for various information tracking purposes. Java Servlet transparently supports HTTP cookies. There are three steps involved in identifying recurring users: The server script sends a series of cookies to the browser. For example, name, age or identification number, etc. The browser stores this information on the local machine for future use. The nex t time the browser sends a request to the web server, it will send the cookie information to the server and the server will use that information to identify you. A servlet will access the cookie via the request.getCookies () request method which returns an array of Cookie objects. Some of the common uses of cookies are: 1. Session authentication uses cookies : 2. Personalized response to the customer based on their preferences, for example, we can set the background color as a cookie in the customer's browser and then use it to customize the background color of the response, image, etc. munotes.in
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8.1.1 Types of cookies : There are 2 types of cookies in servlets : 1. Non-persistent cookie 2. Persistent cookie Non-persistent cookie : It is valid for one session only. It is removed ev ery time the user closes the browser. Persistent cookie : It is valid for multiple sessions. It is not removed every time the user closes the browser. It is removed only if the user logs out or logs out. Advantage of cookies : 1. The simplest technique for main taining the state. 2. Cookies are stored on the client side. Disadvantage of cookies : 1. It will not work if cookies are disabled in the browser. 2. Only textual information can be set in the Cookie object. 3. Cookie class 4. javax.servlet.http.Cookieclass provides the f unctionality of using cookies. Provides many useful methods for cookies. 5. Cookie class constructor Builder Description Cracker() build a biscuit. Cookie (string name, string value) constructs a cookie with a specified name and value.
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Cookies 97 1.2 How do cooki es work?
By default, each request is considered a new request. In the cookie technique, we add cookies with the response of the servlet. The cookies are then stored in the browser cache. Subsequently, if the user submits the request, the cookie is added with the request by default. Therefore, we recognize the user as the previous user. 8.1.3 Cookie Servlet Modes : public void setDomain (string schema) • This method sets the domain to which the cookie applies, for example google.com. public String getDomain () • This method gets the domain to which the cookie applies, for example google.com. public void setMaxAge (expiration int) • This method sets the time (in seconds) that must elapse before the cookie expires. public int getMaxAge () • This method returns th e maximum age of the cookie, specified in seconds. By default, -1 indicates that the cookie will persist until the browser is deactivated. public String getName () • This method returns the name of the cookie. The name cannot be changed after creation. publ ic void setValue (String newValue) • This method sets the value associated with the cookie. munotes.in
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Enterprise Java 98 public String getValue () • This method gets the value associated with the cookie. public void setPath (String uri) • This method sets the path to which this cookie ap plies. public String getPath () • This method gets the path to which this cookie is applied. public void setSecure (boolean flag) • This method sets the Boolean value that indicates whether the cookie should be sent only over encrypted connections (i.e. SSL) . public void setComment (purpose of string) • This method specifies a comment that describes the purpose of a cookie. The comment is useful if the browser presents the cookie to the user. public string getComment () • This method returns the comment describ ing the purpose of this cookie or null if the cookie contains no comments. 8.2 COOKIE SETTINGS WITH SERVLET Setting up cookies with servlets involves three steps: (1) Creation of a Cookie object : You call the cookie constructor with a cookie name and a co okie value, both are strings. Cookie cookie = new Cookie ("name", "value"); Note that neither the name nor the value must contain spaces or any of the following characters: [] () =, "/? @:; (2) Set the maximum age : Use setMaxAge to specify how long (in se conds) the cookie should be valid. The following would set a cookie for 24 hours. cookie.setMaxAge (60 * 60 * 24); (3) Sending the cookie to the HTTP response headers : Use response.addCookie to add cookies in the HTTP response header as follows response .addCookie (cookie); munotes.in
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Cookies 99 8.3 WHERE ARE COOKIES USED? Create a temporary session where the site remembers in some way in the short term what the user was doing or had chosen from the requests of the web page, for example: Who the user is currently logged into. What the user has ordered in an online shopping cart. To remember low -security information more permanently, for example: A user's search results preferences. What topic did the user browse during the user's last visit? For advertising purposes or to impr ove the functionality of a site. Identify a user during an e -commerce session. To avoid entering your username and password to access the site. 8.3.1 Applications : Shopping cart request Bank online Generation of a visitor's profile Generation of a visitor' s profile Website monitoring 8.4 WHERE ARE COOKIES PLACED? By default, all cookies generated are stored on the hard drive of the user's local computer. The locations are different but the cookie format is the same. Use the search function to get the cook ie directory. It expires after a certain time. How to create a cookie? : Cookie ck =new one Cracker("user", "sonoo jaiswal"); // creation of a cookie object response.addCookie (ck);// adding cookies in response How to delete the cookie? Cookie ck =new one Cracker("Username", ""); // removing the value of the cookie munotes.in
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Enterprise Java 100 ck.setMaxAge (0); // change the maximum age to 0 seconds response.addCookie (ck);// adding cookies in response How to get cookies? Cookie ck [] = request.getCookies (); from(In t i =0; i out.print" " + ck [i] .getName () + "" + ck [i] .getValue ()); // print the name and value of the cookie } 8.5 SIMPLE EXAMPLE OF A SERVLET COOKIE In this example, we are storing the user's name in the cookie object and accessing it in another servlet. As we all know, that session corresponds to the particular user. So, if you log in from too many browsers with different values, you will get a different value.
index.html Name:
FirstServlet.java importjava.io. *; importjavax.servlet. *; importjavax.servlet.http. *; public class FirstServlet it extends HttpServlet { public empty doPost (HttpServletRe quest request, HttpServletResponse response) { to deal{ response.setContentType ("text / html"); PrintWriter out = response.getWriter (); munotes.in
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Cookies 101 String n = request.getParameter ("Username"); out.print"Welcome" + n); Cookie ck =new one Cracker("one", n ); // creation of a cookie object response.addCookie (ck);// adding cookies in response // create the submit button out.print"
"); out.close (); }capture(Exception e) {System.out.println (e);} } } SecondServlet.java importjava.io. *; importjavax.servlet. *; importjavax.servlet.http. *; public class SecondServlet it extends HttpServlet { public empty doPost (HttpServletRequest request, HttpServlet Response response) { to deal{ response.setContentType ("text / html"); PrintWriter out = response.getWriter (); Cookie ck [] = request.getCookies (); out.print"Hello" + ck [0] .getValue ()); out.close (); } capture(Exception e) { System.out.p rintln (e); } } } 8.6 SUMMARY A cookie is a bit of information sent by a web server to a browser that can later be read back from that browser. When a browser receives a cookie, it saves the cookie and thereafter sends the cookie back to the server eac h munotes.in
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Enterprise Java 102 time it accesses a page on that server, subject to certain rules. Because a cookie's value can uniquely identify a client, cookies are often used for session tracking. 8.7 REFERENCES https://www. javatpoint.com/java -tutorial https://www.tutorialspoint.com/java/index.htm https://www.geeksforgeeks.org/java/ https://www.oracle.com/in/java/technologies/java -ee-glance.html https://developers.redhat.com/topics/enterprise -java https://www.javacodegeeks.com/enterprise -java-tutorials 8.8 QUESTIONS 1. Explain the cookies with your use. 2. What types of cookies are there? Provide advantages and disadvantages of coo kies with their builders. 3. How do cookies work? Explain your methods. 4. Where are cookies used? Give your applications. Explain the syntax to create and delete the obtained cookies. 5. Provide an example of Cookie.
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103 9 SESSIONS Unit Structure 9.1 Introduction 9.1.1 Advantages of stateless nature 9.1.2 Disadvantages of the stateless nature 9.1.3 Solutions 9.2 How the session works 9.2.1 HttpSession interface 9.2.2 How to get the HttpSession object? 9.2.3 Commonly us ed methods of the HttpSession interface 9.2.4 Solution 9.3 Session ID 9.3.1 Session life cycle 9.3.2 Session Monitoring API 9.3.3 Session Monitoring Methods 9.3.4 Session Management API 9.3.5 Example of using HttpSession 9.4 Summary 9.5 References 9.6 Questions 9.1 INTRODUCTION Session simply means a particular time interval. Session monitoring it is a way to maintain the state (data) of a user. Also known as servlet session management. The HTTP protocol is stateless, so we need to maintain state thro ugh session tracking techniques. Each time the user requests the server, the server treats the request as a new request. Therefore, we need to maintain a user's status to recognize a particular user. HTTP is stateless, which means that each request is trea ted as the new request. All requests and responses are independent. But sometimes it is necessary to monitor customer activity on multiple requests. For example. When a user logs into your website, regardless of which web page they visit after logging in, their credentials will remain on the server until they log off. Then this is handled by creating a session. The session is used to store everything we can get from the client of all the requests the client makes. munotes.in
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Enterprise Java 104 9.1.1 Advantages of stateless nature : Keep s the protocol simple and straightforward Consume fewer resources on the web server. Can admit simultaneous visitors. 9.1.2 Disadvantages of the stateless nature : The increased overhead required a new connection to be created with each request. The inabili ty to track a single visitor crossing a website. The web server cannot automatically accept the browser request with a particular session. 9.1.3 Alternative solutions : Web applications have used several techniques to circumvent HTTP stateless operations: 1. The client is identified each time it makes a request and the server stores and retrieves data related to that client - Sessions 2. The server sends the data to the client and forces the client to return them at each request made - Cookies 9.2 HOW THE SESSION WORKS
The concept behind the session is that, whenever a user starts using our application, we can save unique identifying information about him, in an object available throughout the application, until it is destroyed. So wherever the user goes, we wil l always have his information and we can always manage which user is doing what. Whenever a user wants to exit your application, destroy the object with its information. munotes.in
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Sessions 105 On the client's first request, the web container generates a unique session ID and ret urns it to the client with a response. This is a temporary session created by the web container. The client returns the session ID with each request. It makes it easier for the web container to identify where the request is coming from. The web container u ses this ID, finds the session that matches the ID, and associates the session with the request. 9.2.1 HttpSession interface :
9.2.2 How to get the HttpSession object? : The HttpServletRequest interface provides two methods to get the HttpSession object: publicHttpSessiongetSession (): Returns the current session associated with this request or, if the request does not have a session, create one. publicHttpSessiongetSession (boolean creation): Returns the current HttpSession associated with this request or, if there is no current session and create is true, it returns a new session. 9.2.3 Commonly used methods of the HttpSession interface : public string getId (): Returns a string that contains the unique identifier value. long public getCreationTime (): Retu rns the time this session was created, measured in milliseconds since midnight on January 1, 1970 GMT.
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Enterprise Java 106 public long getLastAccessedTime (): Returns the last time the client sent a request associated with this session, as the number of milliseconds since m idnight January 1, 1970 GMT. public void invalidate (): Replace this session and then unlink all objects linked to it. In a typical stateless protocol transaction, the client: 1. Establishes a connection to the web server 2. Submit a request 3. Get an answer 4. Close connection Because a persistent connection is not maintained between such requests, the connection from the web servers to the client is broken after the connection is closed. Disconnection between a client and the web server entails the following limitat ions: • If the web server requires client authentication, for example a client needs to log in, the client needs to log in again on each request. The web server does not realize that it has already authenticated this client because the connection between the two has been lost. • The web server cannot distinguish one client from another. 9.2.4 Solution : • Establish a permanent connection between the client and the web server. • Visitor's web browser requests. • The web server assigns session IDs to each request. • The w eb server identifies visitors through virtual connections called sessions. 9.3 SESSION ID A session ID is a unique number that a website server assigns to a specific user during that user's visit (session). The session ID can be stored as a cookie, form f ield or URL (Uniform Resource Locator). Some web servers generate session IDs simply by incrementing static numbers. However, most servers use algorithms that involve more complex methods, such as taking into account the date and time of the visit along wi th other variables defined by the server administrator. munotes.in
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Sessions 107 9.3.1 Session life cycle : • A visitor, using a web browser, requests a resource from the web server. • The web server offers the authentication form which causes the visitor's web browser to display a lo gin form. • The web browser returns the username and password, which are then returned to the web server. • The web server returns a valid session ID to uniquely identify this visitor. • The visitor's web browser sends any number of requests to the web server. T he web server identifies users based on session IDs. • The visitor closes the browser without explicitly logging out. 9.3.2 Session Monitoring API : • The session monitoring API is based on the first four methods. This is to help the developer minimize the over head of session monitoring. This type of session tracking is provided by the underlying technology. Let's take the example of the Java servlet. The servlet container handles session tracking activity and the user does not need to explicitly do this using J ava servlets. This is the best of all methods, because all handling and errors related to session monitoring will be handled by the container itself. • Each server client will be mapped to a javax.servlet.http.HttpSession object. Java servlets can use the se ssion object to store and retrieve Java objects during the session. Session monitoring is best when implemented using the session monitoring API. • A session is a collection of HTTP requests, over a period of time. A session is user specific and a new sessio n is created for each user to track all user requests. In the servlet session, tracing can be used to track user state. Session monitoring is also known as session management, it is a mechanism used to maintain a user's state within a set of requests for a period of time. We can say that session monitoring is a means of keeping track of session data. This data represents the data that is transferred in a session. 9.3.3 Session Monitoring Methods : • User authentication : This is the very common way that the use r can provide authentication credentials from the login page and then we can pass the authentication information between the server and the client to maintain the session. This is not a very effective method because it will not work if the same user is log ged in from different browsers. munotes.in
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Enterprise Java 108 • HTML hidden field : We can create a unique hidden field in the HTML and when the user starts browsing we can set its unique value for the user and keep track of the session. This method cannot be used with bindings because it requires the form to be submitted each time a client -to-server request is made with the field hidden. Also, it's not safe because we can get the hidden field value from the HTML source and use it to hack the session. • URL rewrite : We can add a session iden tifier parameter with each request and response to keep track of the session. This is very tedious because we have to keep track of this parameter in every response and make sure it doesn't collide with other parameters. • Cookies : Cookies are small pieces o f information sent by the web server in the response header and stored in the browser's cookies. When the client makes an additional request, it adds the cookie to the request header and we can use it to track the session. We can maintain a session with co okies, but if the client disables cookies, it will not work. 9.3.4 Session Management API : The Session Management API builds on the previous methods for session monitoring. Some of the major disadvantages of all of the above methods are: 1. Most of the time we don't just want to keep track of the session, we need to store some data in the session that we can use in future requests. This will require a lot of effort if we try to implement it. 2. All of the above methods are not complete by themselves, they will not all work in a particular scenario. So we need a solution that can use these session tracking methods to provide session management in all cases. 9.3.5 Example of using HttpSession : In this example, we're setting the session -scope attribute in one servl et and getting that value from the session -scope in another servlet. To set the attribute within the session, we used the setAttribute () method of the HttpSession interface and to get the attribute we used the getAttribute method. index.html :
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Sessions 109 importjavax.servlet. *; importjavax.serv let.http. *; Public class ValidateextendsHttpServlet { protected void doPost (HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { response.setContentType ("text / html; character set = UTF -8"); String name = request.getParameter ("user"); String pass = request.getParameter ("pass"); if (pass.equal ("1234")) { HttpSessionsession = request.getSession (); session.setAttribute ("user", name); response.sendRedirect ("Welcome"); }}} Welcome.java : import java.io. *; importjavax.servlet. *; importjavax.servlet.http. *; public class WelcomeextendsHttpServlet { protected void doGet (HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { response.setContentType ("text / html; character set = UTF -8"); PrintWriterout = response.getWriter (); HttpSessionsession = request.getSession (); String user = (String) session.getAttribute ("user"); out.println ("Hello" + user); }} 9.4 SUMMARY The session object is used to record the acces s status of each client within the session scope, so that it is easy to track the operation status of each client, and the information stored in the session can obtain the valid data of these sessions when the browser makes subsequent requests. In the jsp page, you can use the session object directly (built -in object of jsp), or you can go back to the session object through pageContext. munotes.in
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Enterprise Java 110 getSession () or request. getSession. Session can save user information and implement shopping cart and other functions. 9.5 REFERENCES https://www.javatpoint.com/java -tutorial https://www.tutorialspoint.com/java/index.htm https://www.geeksforgeeks.org/java/ https://www.oracle.com/in/java/technologies/java -ee-glance.html https://developers.redhat.com/topics/enterprise -java https://www.javacodegeeks.com/enterprise -java-tutorials 9.6 QUESTIONS 1. Define the sessions. Explain sessi on monitoring with the advantages and disadvantages of the stateless nature of the HTTP protocol. 2. How does the session work? Explain with the diagram. 3. How does the HTTP session work? Explain with the diagram. 4. Explain the steps for the stateless protocol tr ansaction with its limitations and solutions. 5. Define the session ID. Explain the session life cycle. 6. What is the Session Monitoring API? Provide methods for session monitoring. 7. Provide an example of an HTTP session to validate the user's password.
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111 10 WORK WITH FILES Unit Structure 10.1 File upload 10.2 Downloading files 10.3 Servlet annotations 10.4 References 10.5 Questions 10.6 Summary 10.1 FILE UPLOAD You can use a servlet with an HTML form tag to allow users to upload files to the server. An uploaded file can be a text file or an image file or any document. Creating a file upload form The following HTM code below creates an upload form. The following are the important points to note: The form method attribute must be set to POSTmethod and t he GET method cannot be used The form enctype attribute must be set to multipart / form -data. The module action attribute should be set to a servlet file that would handle uploading files to the backend server. The following example uses the UploadServlet servlet to upload the file. To upload a single file, you need to use a single tag with attribute type = "file". To allow multiple file uploads, include more than one input tag with different values for the name attribute. The browser associates each of them with a Browse button.
File upload module
Upload file:
Select a file to upload:
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This will display the following output wh ich will allow you to select a file from the local PC and when the user clicks "Upload File" the form will be sent along with the selected file.
Write backend servlet Below is the UploadServlet servlet that would take care of accepting the uploaded file and storing it in the / webapps / data directory. This directory name can also be added using an external setting such as a context -param element in web.xml as follows: .... L ocation to store the uploaded file upload file c: \ apache -tomcat -5.5.29 \ webapps \ data \
....
Below is the UploadServlet source code, which can h andle uploading multiple files at the same time. Before proceeding, you should make sure of the following: The following example depends on FileUpload, so make sure you have the latest version of the commons -fileupload.xxjar file in your classpath. You can download it from https://commons.apache.org/fileupload/ . munotes.in
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Work with Files 113 FileUpload depends on Commons IO, so make sure you have the latest version of the commons -io-xxjar file in your classpath. You can download i t from https://commons.apache.org/io/ . When testing the following example, a file smaller than maxFileSize must be loaded; otherwise the file will not be loaded. Make sure you have created the c: \ temp and c: \ apache -tomcat8.0.28 \ webapps \ data directories well in advance. // Import the necessary Java libraries import java.io. *; import java.util. *; import javax.servlet.ServletConfig; import javax.servlet.ServletException; import javax.servlet.http.HttpS ervlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import org.apache.commons.fileupload.FileItem; import org.apache.commons.fileupload.FileUploadException; import org.apache.commons.fileupload.disk.DiskFile ItemFactory; import org.apache.commons.fileupload.servlet.ServletFileUpload; import org.apache.commons.io.output. *; The UploadServlet public class extends HttpServlet { isMultipart private boolean; FilePath private string; private int maxFileSize = 50 * 1024; private int maxMemSize = 4 * 1024; private archive file; public void init () { // Get the location of the file where it would be stored. filePath = getServletContext (). getInitParameter ("file upload"); } public void doPost (HttpServletReque st request, HttpServletResponse response) throw ServletException, java.io.IOException { // Check that we have a request to upload the file isMultipart = ServletFileUpload.isMultipartContent (required); response.setContentType ("text / html"); munotes.in
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Enterprise Java 114 java.io. PrintWriter out = response.getWriter (); if (! isMultipart) { out.println (""); out.println ("
"); out.println (""); out.println (""); Return; } DiskFileItemFactory factory = new DiskFileItemFactory (); factory.setSizeThreshold (maxMemSize); // maximum size to be stored in memory factory.setRepository (new File ("c: \\ temp")) ; // Location to save data larger than maxMemSize. ServletFileUpload upload = new ServletFileUpload (factory); // Create a new file upload controller upload.setSizeMax (maxFileSize); // maximum size of the file to upload. to deal { List fileItems = uploa d.parseRequest (required); // Parse the request to get the elements of the file. Iterator i = fileItems.iterator (); // Process the elements of the uploaded file out.println (""); out.println (""); out.println (" Loading servlet </tit le>"); <br> out.println ("</head>"); <br> out.println ("<body>"); <br> while (i.hasNext ()) { <br> FileItem fi = (FileItem) i.next (); <br> if (! fi.isFormField ()) { <br> // Get the parameters of the uploaded file <br> String fieldName = fi.getFieldName (); <br> String filename = fi.g etName (); <br> String contentType = fi.getContentType (); <br> isInMemory = fi.isInMemory (); munotes.in</p>
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<p> <br> Work with Files <br>115 long sizeInBytes = fi.getSize (); <br> // Write the file <br> if (fileName.lastIndexOf (" \\")> = 0) { <br> file = new file (file path + file name.substring (file name.lastIndexOf <br>("\\"))); <br> } the rest { <br> file = new file (file path + file name.substring (file name.lastIndexOf <br>("\\") + 1)); <br> } <br> fi.write (file); <br> out.println ("Uploaded file name:" + file name + "<br>"); <br> } <br> } <br> out.println ("</body>"); <br> out.println ("</html>"); <br> } catc h (ex exception) { <br> System.out.println (es); <br> }} <br> public void doGet (HttpServletRequest request, HttpServletResponse <br>response) <br> throw ServletException, java.io.IOException { <br> throw a new ServletException ("GET method used with" + <br> getClass () .getName () + ": POST method is required."); <br> }}} <br>10.2 DOWNLOADING FILES In this example, we are creating three files: <br> index.html <br> DownloadServlet.java <br> web.xml <br>index.html <br>This file provides a link to download the file. <br><a href="servlet/DownloadServlet"> download the jsp file </a> <br>DownloadServlet.java <br>importjava.io. *; <br>import javax.servlet.ServletException; munotes.in</p>
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<p> <br> Enterprise Java <br>116 importjavax.servlet.http. *; <br>public class DownloadServlet extends HttpServlet { <br>public void doGet (HttpServletRequest request, HttpServletResponse <br>response) throws ServletException, IOException { <br>response.setContentType ("text / html"); <br>PrintWriter out = response.getWriter (); <br>String filename = "home.jsp"; <br>String file path = "e: \\"; <br>response.setContentType ("APPLICATION / OCTETO -STREAM"); <br>response.setHeader (" Content -Disposition", "attachment; filename = \" "+ <br>filename +" \ ""); <br>FileInputStream fileInputStream = new FileInputStream (file path + file <br>name); <br>In t I; <br>weather ((i = fileInputStream.read ())! = -1) { <br>out.write (i); <br>} <br>fileInputStream.close (); <br>out.close (); <br>}} <br>web.xml file <br><web -app> <br><servlet> <br><servlet -name> DownloadServlet </servlet -name> <br><servlet -class> DownloadServlet </servlet -class> <br></servlet> <br><mapping -servlet> <br><servlet -name> DownloadServlet </servlet -name> <br><url-pattern> / servlet / DownloadServlet </url -pattern> <br></servlet -mapping> <br></web -app> <br>10.3 SERVLET ANNOTATIONS Servlet uses the deployment descriptor (web.xml file) to deploy the <br>application to a web server. Servlet API 3.0 introduced a new package <br>called javax.servlet.annotati on. Provides annotation types that can be <br>used to annotate a servlet class. If you use annotation, the deployment munotes.in</p>
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<p> <br> Work with Files <br>117 descriptor (web.xml) is not required. But you should be using <br>Tomcat7 or any later version of Tomcat. <br> Annotations can override the equivalent XML configuration in the <br>web deployment descriptor file (web.xml), such as the servlet <br>declaration and servlet mapping. Servlet containers will process the <br>classes noted at the time of deployment. The types of annotations <br>introduced in Servlet 3.0 are: Sr.No. Annotation and description 1 @WebServlet: Declare a servlet. 2 @WebInitParam: To specify an initialization parameter. 3 @WebFilter: Declare a servlet filter. 4 @WebListener: To declare a WebListener 5 @HandlesTypes: Declare the types of classes th at a <br>ServletContainerInitializer can handle. 6 @HttpConstraint: This annotation is used within the <br>ServletSecurity annotation to represent security <br>restrictions that will apply to all HTTP protocol methods <br>for which a corresponding HttpMethodConstraint <br>element is NOT produced within the ServletSecurity <br>annotation. 7 @HttpMethodConstraint: This annotation is used within the ServletSecurity annotation to represent security restrictions on specific HTTP protocol messages. 8 @MultipartConfig: An annotation that can be specified in a Servlet class, indicating that Servlet instances expect requests that conform to the multipart / form-data MIME type. 9 @ServletSecurity: This annotation is used in a Servlet implementation class to specify the security restrictions that a Servlet container must apply on HTTP protocol messages. <br>10.4 REFERENCES https://www.javatpoint.com/java -tutorial <br> https: //www.tutorialspoint.com/java/index.htm <br> https://www.geeksforgeeks.org/java/ <br> https://www.oracle.com/in/java/technologie s/java -ee-glance.html <br> https://developers.redhat.com/topics/enterprise -java <br> https://www.javacodegeeks.com/ente rprise -java-tutorials <br> munotes.in</p>
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<p> <br> Enterprise Java <br>118 10.6 SUMMARY <br> <br> <br>10.5 QUESTIONS 1. Take an example to upload a file. <br>2. Take an example to download a file. <br>3. Explain the different servlet annotations <br>***** <br>munotes.in</p>
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<p> 113 11 <br>NON-BLOCKING <br>Unit Structure <br>11.1 Introduction to I / O <br>11.1.1 Why NIO? <br>11.2 Stream against blocks <br>11.3 Integrated I / O integrated <br>11.4 I / O. blocking and non -blocking <br>11.5 Read from a file <br>11.5.1 Write to file <br>11.6 Listeners <br>11.7 Steps to im plement WriteListener <br>11.8 Steps to implement ReadListener <br>11.9 Summary <br>11.10 References <br>11.11 Questions <br>11.1 INTRODUCTION TO I / O I / O, or input / output, refers to the interface between a computer and <br>the rest of the world, or between a single progra m and the rest of the <br>computer. It is such a crucial element of any computer system that <br>most of any I / O is built into the operating system. Individual <br>programs generally do most of the work for them. <br> In Java programming, I / O has until recently been do ne using a flow <br>metaphor. All I / O is considered to be moving individual bytes, one <br>at a time, through an object called Stream. Stream I / O is used to <br>contact the outside world. It is also used internally, to convert objects <br>to bytes and then back to obj ects. <br> NIO has the same function and purpose as the original I / O, but uses <br>a different metaphor: block I / O. As you will learn in this tutorial, <br>block I / O can be much more efficient than streaming I / O. <br>11.1.1 Why NIO? : <br>NIO was created to allow Java p rogrammers to implement high -speed I / <br>O without having to write custom native code. NIO shifts more time -<br>consuming I / O tasks (that is, buffering and flushing) to the operating <br>system, allowing for a noticeable increase in speed. <br> <br> munotes.in</p>
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<p> <br> Enterprise Java <br>114 11.2 STREAM AGAINST BL OCKS The most important distinction between the original I / O library <br>(found in java.io. *) and NIO has to do with how data is packaged and <br>transmitted. As mentioned earlier, the original I / O takes care of the <br>data in streams, while the NIO takes care o f the data in chunks. <br> A flow -oriented I / O system handles data one at a time. An input <br>stream produces one byte of data and an output stream consumes one <br>byte of data. It is very easy to create filters for the transmitted data. It <br>is also relatively easy to chain multiple filters together so that each <br>plays its part in a unique and sophisticated processing mechanism. On <br>the other hand, streaming -oriented I / O is usually quite slow. <br> A block -oriented I / O system manages the data in blocks. Each <br>operation p roduces or consumes a block of data in a single step. The <br>data processing by the block can be much faster than the byte <br>processing (transmitted). But block -oriented I / O lacks the elegance <br>and simplicity of flow -oriented I / O. <br>11.3 INTEGRATED I / O INTEG RATED The original I / O package and NIO have been well integrated into <br>JDK 1.4. java.io. * was redeployed using NIO as a base, so you can <br>now take advantage of some NIO features. For example, some of the <br>classes in the java.io package. * contain methods f or reading and <br>writing data in blocks, leading to faster processing even on more <br>flow-oriented systems. <br> You can also use the NIO library to implement standard I / O <br>functions. For example, you can easily use I / O blocks to move data <br>one byte at a time. Bu t as you will see, NIO also offers many benefits <br>that are not available in the original I / O package. <br>11.4 IO BLOCKING AND NON -BLOCKING Various Java I / O streams are blocked. This means that when a thread <br>calls alight() or write(), that thread is blocked until there is no data to <br>read or until the data is completely written. The thread can't do <br>anything else in the meantime. <br> Java NIO's non -blocking mode allows a thread to request to read data <br>from a channel and get only what is currently available, or not hing, if <br>no data is currently available. Instead of getting stuck until the data is <br>available for reading, the thread can continue with something else. <br> The same goes for non -blocking writing. A thread may request some <br>data to be written to a channel, but n ot wait for it to be fully written. <br>The thread can continue and do something else in the meantime. <br> Whereas threads spend their idle time when they aren't blocked during <br>I / O calls, they are generally doing I / O on other channels in the munotes.in</p>
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<p> <br> Non-Blocking <br>115 meantime. That is, a single thread can now handle multiple input and <br>output channels. <br>11.5 READ FROM A FILE If we were using the original I / O, we would simply create a <br>FileInputStreamand read it. In NIO, however, things work a little <br>differently: first we get aChannel obj ect of FileInputStreamand then <br>use that channel to read the data. <br> Whenever you perform a read operation on a NIO system, you are <br>reading from a channel, but not reading directly from a channel. Since <br>all data ultimately resides in the buffer, it is read fr om a channel to a <br>buffer. <br> So, reading from a file involves three steps: (1) getting the Channel <br>from FileInputStream; (2) create theBumper; and (3) reading <br>theCannel to Bumper. Now, let's see how it works. <br>Three simple steps: <br>Our first step is to get a cha nnel. We take the channel <br>fromFileInputStream: FileInputStream fin = new FileInputStream ("readandshow.txt"); FileChannel fc = fin.getChannel (); <br>The next step is to create a buffer: ByteBuffer buffer = ByteBuffer.allocate (1024); <br>And finally, we ne ed to read from channel to buffer, as shown here: fc.read (buffer); <br>11.5.1 WRITE TO FILE Writing to a file in NIO is similar to reading from one. Let's start by <br>getting a channel from toFileOutputStream: FileOutputStream fout = new FileOutputStream ("writesomebytes.txt"); FileChannel fc = fout.getChannel (); munotes.in</p>
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<p> <br> Enterprise Java <br>116 Our next step is to create a buffer and insert data into it; in this case the <br>data will be taken from a named arrayMessage A containing the ASCII <br>bytes for the string "Some bytes". ByteBuffer buff er = ByteBuffer.allocate (1024); <br> for (int i = 0; i <message.length; ++ i) { <br> buffer.put (message [i]); <br>} <br>buffer.flip (); <br> Our last step is to write to the buffer: fc.write (buffer); <br>11.6 LISTENERS Java EE provides non -blocking I / O support for servlet s and filters when <br>processing requests in asynchronous mode. The following steps <br>summarize how to use non -blocking I / O to process requests and write <br>responses within the service's methods. <br> Put the request in asynchronous mode as described in Asynchronous <br>Processing. <br> Get an inflow and / or outflow from the request and response objects <br>in the service method. <br> Assign a read listener to the input stream and / or a write listener to <br>the output stream. <br> Process the request and response within the listener's callb ack <br>methods <br>Non-blocking I / O support in javax.servlet.ServletInputStream Method Description void setReadListener (ReadListener rl) Associate this input stream with a listener that contains callback methods to read the data asynchronously. Provide the listener as an anonymous class or use another mechanism to pass the input stream to the read listener. boolean isReady () Returns true if the data can be read without blocking. munotes.in</p>
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<p> <br> Non-Blocking <br>117 boolean isFinished () Returns true when all data has been read. Non-blocking I / O support in javax.servlet.ServletOutputStream Method Description void setWriteListener (WriteListener wl) Associate this output stream with a listener that contains callback methods for writing data asynchronously. Provide the write listener as an anonymous class or use another mechanism to pass the output stream to the write listener boolean isReady () Returns true if the data can be <br>written without locks. Listening interfaces for non -blocking I / O support Interface methods Description Read Listener void onDataAvailable () <br>void suAllDataRead () <br>void onError <br>(Throwable t) TO ServletInputStream The <br>instance calls these methods <br>on its listener when data is <br>available to read, when all <br>data has been read, or when <br>an error occurs. Write Listener void onWritePossible () void onError (Throwable t) TO ServletOutputStream The instance calls these methods in its listener when it can write data without blocking or when an error occurs. <br>11.7 S TEPS TO IMPLEMENT WRITELISTENER 1. In the Projects tab, right -click on your project and say Html5 and <br>Servlet 3.1 and select New> Other. <br> munotes.in</p>
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<p> <br> Enterprise Java <br>118 2. In the New File dialog box, complete the following steps on the <br>Choose File Type page: <br>a. Select Java in Categories. <br>b. Select Java Class in File Types. <br>c. Click Next. <br> <br>3. On the New Java Class page , do the following: <br>a. Pay in Write ListenerImpl as the name of the class. <br>b. Pay in com.example as the package name. <br>c. Click Finish. <br> <br>4. Import the following packages: <br>Import java.io.IOException; <br>importjava.util.Queue; munotes.in</p>
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<p> <br> Non-Blocking <br>119 importjavax.servlet.AsyncContext; <br>importjavax.s ervlet.ServletOutputStream; <br>import javax.servlet.WriteListener; <br>5. Modify the class to implement the Write Listener Interface. <br>The public class WriteListenerImpl implements WriteListener { <br>6. Declare the following variables: <br>ServletOutputStreamprivateoutput=null ; <br>privatequeue=null; <br>private AsyncContext context = null; <br> <br>7. Add a constructor to the class: <br>WriteListenerImpl (ServletOutputStream s os, Queue q, AsyncContext c) { <br>output=sos; <br>tail=q; <br>context = c; } <br> <br>8. Add the onWritePossible () method: <br>publicvoidonWritePossi ble()throwsIOException{ <br>while (queue.peek ()! = null && output.isReady ()) <br>Datastring= (String)queue.poll (); <br> output.print (data); munotes.in</p>
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<p> <br> Enterprise Java <br>120 } <br> if (queue.peek () == null) { <br> context.com complete (); <br> }} <br> <br>9. Add the onError method. <br>public void onError (final Thro wable t) { <br> context.complete (); <br>t.printStackTrace (); } <br> <br>11.8 STEPS TO IMPLEMENT READLISTENER Perform the following steps to implement the ReadListenerImpl class: <br>1. On the Projects tab, right -click Html5 and Servlet3.1 and select New> <br>Other. munotes.in</p>
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<p> <br> Non-Blocking <br>121 <br> <br>2. In the New File dialog box, complete the following steps on the <br>Choose File Type page: <br>a. Select Java in Categories. <br>b. Select Java Class in File Types. <br>c. Click Next. <br>3. On the New Java Class page, do the following: <br>a. Pay in ReadListenerImpl as the name of the class. <br>b. Pay in com.e xample as the package name. <br>c. Click Finish. <br>4. Import the following packages: <br>import java.io.IOExc eption; import java.util.Queue; <br>import java.util.concurr ent.LinkedBlockingQueue; import <br>javax.servlet.AsyncContext; import jav ax.servlet.ReadListener; import <br>javax .servlet.ServletInputStream; import <br>javax.serv let.ServletOutputStream; import <br>javax.Lxistepnervlet.Write.Write .HttpServletResponse; <br>5. Modify the class to implem ent the Read Listener Interface: <br>The public ReadListenerImpl class implements ReadListener <br> <br> munotes.in</p>
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<p> <br> Enterprise Java <br>122 6. Decl are the following variables: <br>private entry ServletInputStream = null; Private HttpServletResponse res <br>= null; Private AsyncContext ac = null; private queue queue = new <br>LinkedBlockingQueue (); <br> <br>7. Add a constructor to the class: <br>ReadListenerImpl (ServletInputS treamin, ttpServletResponser, <br>AsyncContext c) {input = in; re = r; ac = c; } <br> <br>8. Add the onDataAvailable () method: <br>public void onDataAvailable () throws IOException {System.out.println <br>("Dataisavailable"); <br>StringBuilder sb = new StringBuilder (); int len = -1; byte b [] = new byte <br>[1024]; while (input.isReady () && (len = input.read (b))! = -1) {String <br>data = new String (b, 0, len); sb.append (data); } queue.add (sb.toString <br>()); } <br> munotes.in</p>
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<p> <br> Non-Blocking <br>123 9. Añade el onAllDataRead ()method: <br>public void onAllDataRead () throws IO Exception {System.out.println <br>("All data is read"); // now all data has been read, set a WriteListener to <br>write the output ServletOutputStream = res.getOutputStream (); <br>WriteListener writeListener = new WriteListenerImpl (output, queue, ac); <br>output.setWrit eListener (writeListener);} <br> <br>10. Add the onError method. : <br>public void onError (final Throwable t) {ac.complete (); t.printStackTrace <br>(); } <br> <br>After ServletInputStream.setReadListener is called, Read Listener in <br>DataAvailablecalled immediately if there is data to read. Otherwise, it is <br>invoked when the data is ready. When all the data has been read,Read <br>Listener establishes a Write Listener to write data in non -blocking mode. <br>11.9 SUMMARY Java NIO's non -blocking mode enables a thread to request reading data <br>from a channel, and only get what is currently available, or nothing at all, <br>if no data is currently available. Rather than remain blocked until data <br>becomes available for reading, the thread can go on with something else. <br> munotes.in</p>
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<p> <br> Enterprise Java <br>124 11.10 REFERENCES https://www.javatpoint.com/java -tutorial <br> https://www.tutorialspoint.com/java/index.htm <br> https://w ww.geeksforgeeks.org/java/ <br> https://www.oracle.com/in/java/technologies/java -ee-glance.html <br> https://de velopers.redhat.com/topics/enterprise -java <br> https://www.javacodegeeks.com/enterprise -java-tutorials <br>11.11 Questions 1. Explain I / O and NIO. Differentiate between flows and blocks. <br>2. Explain embedded I / O with the difference between blocking and <br>non-blocking I / O. <br>3. How to read and write files? Give an example. <br>4. Tell listeners how to read and write a file. <br>5. Explain the steps to implement WriteListener. <br>6. Explain the steps for ReadListener. <br> <br> <br>***** <br> <br>munotes.in</p>
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<p> 125 UNIT III <br>12 <br>INTRODUCTION TO JAVA SERVER <br>PAGES <br>Unit Structure <br>12.0 Objectives <br>12.1 Introduction to Java Server Pages <br>12.2 Why use Java Server Pages? <br>12.3 Disadvantages of JSP <br>12.4 JSP v/s Servlets <br>12.5 Lifecycle of a JSP Page <br>12.6 How does a JSP fu nction? <br>12.7 How can a JSP Program be executed? <br>12.8 Directory Structure of JSP <br>12.9 Summary <br>12.10 List of References <br>12.11 Questions <br>12.0 OBJECTIVES After going through this chapter, you will: <br> Understand the basics of Java Server Pages technology <br> Learn the advantages and disadvantages of JSP <br> Differentiate between JSP and Servlets <br> Understand lifecycle of a JSP program <br> Learn how to execute a JSP program <br>12.1 INTRODUCTION TO JAVA SERVER PAGES Java Server Pages (JSP), a server side technology, which is a pa rt of Java <br>EE framework, is used for creating dynamic web applications in a very <br>simple yet powerful way. JSP technology allows you to develop JSP pages <br>which are text based documents that processes a request and generates a <br>response. It has access to the powerful enterprise Java API including the <br>JDBC API and hence can be used to access enterprise databases. <br>A JSP Page consists of both static and dynamic content. The static content <br>can be written using plain HTML or XML and dynamic content can be <br>written either using the regular java style of programming embedded in <br>specific elements or using the tag style approach. This eliminates the need <br>of writing multiple println statements that generate HTML like in Servlets. munotes.in</p>
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<p> <br> Enterprise Java <br>126 JSP provides developers with the ability to cleanly separate the application <br>logic from the presentation logic. In other words, JSP can easily <br>differentiate the coding in the view layer and application logic layer. <br>Hence any requirement changes that is needed to be done in the look and <br>feel of t he web application can very easily be done as it would require <br>changes only in the HTML part of code and not the logical part written in <br>java, thus eliminating the need to recompile the entire web application <br>again. <br>It also supports unified expression lan guage (UEL) to access server <br>objects without having explicit need to declare them. <br>The file extension for JSP pages is .jsp <br>12.2 WHY USE JAVA SERVER PAGES JSP has the following benefits: <br>1. Nobody can borrow the code : <br>Since JSP page are written, runs and r emains on the server, nobody can <br>copy the logic written in a jsp page even if they wanted to. Thus, security <br>of the code is maintained. <br>2. Faster loading of pages : <br>Response page customization as requested by the user is done at the server <br>side itself thus no extra code or content is sent to the client side resulting <br>in faster loading of pages. <br>3. No Browser compatibility issues : <br>Since JSP runs on the server side, the developer ends up sending standard <br>HTML to the user browser. This largely eliminates cross browser <br>compatibility issues. <br>4. JSP Support : <br>JSP is supported by a number of Web Servers. Built -in Support for JSP is <br>available in Java Web Server from Oracle. <br>5. Compilation : <br>In JSP technology, each JSP page is compiled into executable code the <br>first ti me it is requested and invokes the resulting code directly on all <br>subsequent requests. When coupled with a persistent JVM, this allows the <br>server to process request to JSP pages much faster. <br>6. Similarity to HTML : <br>A JSP page looks a lot like a HTML or XML page except for the business <br>logic written either in scripting elements or JSP tags or both. Writing the <br>business logic in JSP tags brings consistency to the coding style used on <br>the entire JSP page. munotes.in</p>
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<p> <br> Introduction to Java Server Pages <br>127 7. Separation of logic from view <br>It enables to separat e presentation layer with the business logic layer in the <br>web application. <br> 12.3 DISADVANTAGES OF JSP The disadvantages of JSP are: <br> 1. Attractive Java code : <br>Putting Java code within a webpage is really bad design, but JSP makes it <br>tempting to do just that . Avoid this as far as possible. <br>2. Java Code Required : <br>To do relatively simple things in JSP can actually demand putting Java <br>code in a page. Assume a page needs to determine the context root of the <br>current web application, perhaps to create a link to the web <br>applications,home page. This is done using Java code in JSP. <br><a href=’<%=request.getContextPath()%> /index.html’>Home Page</a> <br>Java code can be avoided by using <jsp:getProperty> but that makes the <br>code spec even more complex. <br><a href=’<jsp:getPropert y name=”request” <br>property=”contextPath”/>/index.html’>Home Page</a> <br>3. Simple Tasks are Hard to Code : <br>Even including page headers and footers is a bit difficult with JSP. In JSP <br>the best way to do this is as follows: <br><% @include file=”/header.jsp”;%> <br>/*Som e content here*/ <br><% @include file=”/footer.jsp”;%> <br>4. Occupies a lot of space : <br> JSP pages require about double the disk space to hold the page. Because <br>JSP pages are translated into class files, the server has to store the resultant <br>class files with the JS P pages. <br>5. Debugging not easy : <br>It is hard to trace JSP pages error because JSP pages are translated to <br>servlet before the compilation process. <br>6. Difficult Looping in JSP : <br>Looping in JSP is a bit complicated. <br> munotes.in</p>
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<p> <br> Enterprise Java <br>128 7. Database Connection not easy : <br>Database co nnectivity is not as easy as it should be. Most of the servlet <br>engine vendors do not support connection pooling natively, as of this day. <br>Consequently, one has to write a lot of custom code to do the job. <br>12.4 JSP V/S SERVLETS Servlets provide the ability to build dynamic content for websites using <br>Java and is supported by all Web Servers. Servlet JSP Servlets run faster than JSP. JSP runs slower than servlet as it takes time to compile the program and convert into servlets. It is hard to write code in servlet. It’s easier to code in JSP compared to servlets. In MVC architecture, servlet works as a controller. In MVC architecture, JSP works as a view for displaying output. It should be use when there is more data processing involved. JSP is generally used when there is no involvement of much data processing. There is no custom tag writing facility in servlets. You can easily build custom tags that can directly call Java beans. Servlet is a java code. JSP is a HTML-based code. It can accept all protocol requests, including HTTP. It can only accept HTTP requests. You can override the service() method. In JSP, you can’t override the service() method. In Servlet, by default, session management is not enabled, user has to enable it explicitly. In JSP, session management is automatically enabled. In Servlet, you have to implement both business logic and presentation logic in the single file. In JSP, business logic is split from presentation logic. Modification in Servlet file is a time consuming due to reloading, recompiling, and restarting the server. JSP modification is fast, as you just need to click one refresh button. munotes.in</p>
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<p> <br> Introduction to Java Server Pages <br>129 12.5 LIFECYCLE OF A JSP PAGE A JSP life cycle is defined as the process from its creation till the <br>destruction. This is similar to a servlet life cycle with an additional step <br>which is required to compile a JSP into servlet. <br>When the browser asks for a JSP, JSP engine first checks whether it needs <br>to compile the page. If the JSP is last compiled or the recent modifi cation <br>is done in JSP, then the JSP engine compiles the page. <br>Compilation process of JSP page involves three steps: <br> Parsing of JSP <br> Turning JSP into servlet <br> Compiling the servlet <br>JSP Lifecycle follows the following steps: <br>1. Translation of JSP page <br>2. Compilatio n of JSP page(Compilation of JSP page into _jsp.java) <br>3. Classloading (_jsp.java is converted to class file _jsp.class) <br>4. Instantiation(Object of generated servlet is created) <br>5. Initialisation(_jspinit() method is invoked by container) <br>6. Request Processing(_jspserv ice() method is invoked by the container) <br>7. Destroy (_jspDestroy() method invoked by the container) <br>1. Translation of the JSP Page: <br>A Java servlet file is generated from a JSP source file. This is the fi rst step <br>of JSP life cycle. In translation phase, container validates the syntactic <br>correctness of JSP page and tag files. <br>The JSP container interprets the standard directives and actions, and the <br>custom actions referencing tag libraries used in this JSP p age. <br>For example, a program named demo.jsp as shown below: <br>demo.jsp <br><html> <br><head> <br><title>Demo JSP
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Count is: <% out.println(demovar++); %>
will get translated into demo_jsp.java as below:
In the ab ove example, demo.jsp, is a JSP where one variable is initialized and incremented. This JSP is converted to the servlet (demo_jsp.class ) wherein the JSP engine loads the JSP Page and converts to servlet content. When the conversion happens all template text is converted to println() statements and all JSP elements are converted to Java code. 2. Compilation of the JSP Page : The generated java servlet file is compiled into java servlet class The translation of java source page to its implementation class can happen at any time between the deployment of JSP page into the container and processing of the JSP page. In the above pictorial description demo_jsp.java is compiled to a class file demo_jsp.class 3. Class loading : Servlet class that has been loaded from JS P source is now loaded into the container 4. Instantiation : In this step the object i.e. the instance of the class is generated. The container manages one or more instances of this class in the response to requests and other events. Typically, a JSP containe r is built using a servlet container. A JSP container is an extension of servlet container as both the container support JSP and servlet. munotes.in
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Introduction to Java Server Pages 131 A JSPPage interface which is provided by container provides init() and destroy () methods. There is an interface HttpJ SPPage which serves HTTP requests, and it also contains the service method. 5. Initialization : public void jspInit() { //initializing the code } _jspinit() method will initiate the servlet instance which was generated from JSP and will be invoked by the con tainer in this phase. Once the instance gets created, init method will be invoked immediately after that It is only called once during a JSP life cycle, the method for initialization is declared as shown above 6. Request processing : void _jspservice(HttpSer vletRequest request HttpServletResponse response) { //handling all request and responses } _jspservice() method is invoked by the container for all the requests raised by the JSP page during its life cycle For this phase, it has to go through all the above phases and then only service method can be invoked. It passes request and response objects This method cannot be overridden The method is shown above: It is responsible for generating of all HTTP methods i.eGET, POST, etc. 7. Destroy : public void _jspdestr oy() { //all clean up code } _jspdestroy() method is also invoked by the container munotes.in
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Enterprise Java 132 This method is called when container decides it no longer needs the servlet instance to service requests. When the call to destroy method is made then, the servlet is ready for a garbage collection This is the end of the life cycle. We can override jspdestroy() method when we perform any cleanup such as releasing database connections or closing open files.
Whenever the JSP file changes ,the Web Server automatically detects the change and rebuilds the corresponding servlet. The JSP to Servlet compilation phase imposes a slight delay the first time a page is retrieved. Many web servers permit pre -compilation of JSPs to get around this problem. 12.6 HOW DOES JSP FUNCTION: JSP code spec can be broken into two categories: Elements that are processed by the JSP Engine on the Web Server Template data or everything other than such elements that the JSP engine ignores. A JSP page is executed by a web server that either has a built -in JSP engine or accesses a third party JSP engine,which it is configured to use. When a client asks for a JSP page , the Web Server sends that request and delivers it to the JSP engine along with a response object. The JSP engine then processes the client’s request and delivers the output back to the Web Server for further delivery to the client. Let’s look into a simple example to understand the functioning of a JSP page. In this example, we are creating a html page to accept a name from the user and submit it to the Server. The Web Server will process the request which will consist the name entered by the user and in return print a “Hello “ name on the client’s browser. Example: Program to understand the basic functioning of a JSP page. Index.html munotes.in
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Introduction to Java Server Pages 133
User Page
When viewed in a browser,the HTML page looks like:
When the user cli cks Submit ,the data entered on the form will be sent as a request to the JSP page on the Web Server for further processing. The Web Server accepts the data returned from the browser and passes it as a parameter to hello.jsp which creates the response HT ML page which will be sent back to the client’s browser.
In the above Hello.jsp page, the first line : <%@page contentType="text/html" pageEncoding="UTF -8"%> is a JSP directive (denoted by <%@). Hence the JSP engine recognizes that: The MIME type is text/html for JSP Style JSP tag. The char acter encoding is UTF -8 for XML style tags. The next part of code <%=request.getParameter("name")%> is a block of expression tag which is used to evaluate the expression after = and return the value . Thus the output of the above code will be Hello followe d by the name entered by the user on index.html. The response from the web server displayed in the user browser is :
12.7 HOW DOES JSP PROGRAM EXECUTE? The following happens when a user browser requests index.jsp. The browser sends its request to the We b Server as http://localhost:8080/Sample/index.jsp?numtimes=5 This specifies the value of numtimes as a GET parameter. Web Server recognizes index.jsp in the URL sent in by the browser. Web Server recognizes index.jsp as a jsp page by its extension and that the information delivered by the browser encoded in the URL must be passed onto index.jsp. Index.jsp is then translated into a java class by the JSP engine, This translation and compilati on phase occurs only when the JSP is first called. (or it is subsequently changed)Hence there will be slight delay the first time when index.jsp is run. munotes.in
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Introduction to Java Server Pages 135 For every subsequent request for that JSP page thereafter, there is no delay because the request is for warded directly to the servlet already in the memory.
12.8 DIRECTORY STRUCTURE OF JSP The directory structure of JSP page is same as Servlet. We contain the JSP page outside the WEB -INF folder or in any directory.
12.9 SUMMARY Java Server Pages is a se rver side technology used for creating dynamic web application. Tags are used to insert JAVA code into HTML pages. JSP is first converted into servlet by JSP container before processing the client’s request. munotes.in
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Enterprise Java 136 JSP easily separates the presentation logic from the business logic JSP code can be easily modified to incorporate any look and feel changes to the application 12.10 LIST OF REFERENCES Java EE 7 for Beginners, Sharanam Shah, Vaishali Shah, First Edition, SPD Web References : 1. https://www.guru99.com 12.11 QUESTIONS Q1. How does JSP differ from Servlets? Q2. Write a note on lifecycle of a JSP. Q3. What are the advantages and disadvantages of using JSP for developing web applications? Q4. How are JSP pages executed? *****
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137 13 GETTING STARTED WITH JAVA SERVER PAGES, ACTION ELEMENTS Unit Structure 13.0 Objectives 13.1 Introduction 13.2 Comments in JSP 13.3 JSP Documents 13.4 JSP Elements 13.5 JSP Directives 13.5.1 Page directive 13.5.2 Include directive 13.5.3 Tag lib directive 13.6 JSP Scripting Elements 13.6.1 Scriptlets Tag 13.6.2 Expressions Tag 13.6.3 Declarations Tag 13.7 JSP Action Elements 13.7.1 13.7.2 13.7.3 13.7.4 13.7.5 13.8 JSP GUI Example 13.9 Summary 13.10 List of References 13.11 Questions 13.0 OBJECTIVES After going through this chapter, you will: Understand Java Server Pages documents Learn the various elements that can be used in a JSP page Lean how to inclu de and forward JSP pages Understand what are Java Beans and why it is used? munotes.in
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Enterprise Java 138 13.1 INTRODUCTION A JSP Page looks very similar to a HTML or XML page. It consists of both static and dynamic content. The static content can be written using plain HTML or XML and dynamic content can be written either using the regular java style of programming embedded in specific elements or using the tag style approach. JSP tags are nothing but holders of Java code spec in an HTML page. This code spec is then executed by the we b server whenever the page is requested. 13.2 COMMENTS IN JSP Comments are text that is written for maintaining JSP pages. These are ignored by the JSP engine when it translates the JSP page into a Servlet. The comment will therefore not be sent to the us er (Web Browser) in the response and thus will not be visible using the browser’s View Source option. There are 2 syntax of writing comments in a JSP page: 1) <%-- This is JSP comment --%> This comment will be ignored by the JSP engine : 2) This is a HTML comment and will be ignored by the browser. Example: Program showing how to write JSP comments
JSP Program to show comments
Hello World! <%-- This is a JSP co mment and will not be processed by JSP Engine --%>
13.3 JSP DOCUMENTS A JSP document can use either the traditional JSP style syntax or XML style JSP syntax within its source file. JSP pages uses the traditional or short -hand syntax, whereas JSP documents are completely XML -compliant. munotes.in
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Getting Started With Java Server Pages, Action Elements 139 JSP documents are also referred to as JSP pages using XML syntax. Following are the advantages of using JSP documents: 1. JSP documents can be easily verified as well -formed XML/HTML. 2. JSP documents can be validated against an XML -Schema. 3. JSP documents can be readily written and parsed using standard XML tools. 4. JSP uses XML compliant include and forward actions as well as custom tags. 5. JSP documents require slightly more developer discipline th an JSP pages. This makes the code spec more readable and maintainable especially to those to whom JSP is new. 13.4 JSP ELEMENTS JSP page usually provide dynamic behaviour. This means they are supposed to change the response as per specific client requests. JSP pages can be given dynamic behaviour by embedding Java code in them. To clearly separate JSP elements are used. It helps to inform the JSP translator which part of code is java and which part is HTML. JSP Elements enclose the Java code in a JSP page a nd are categorized as follows: 1. Directives 2. Scripting Elements 3. Action Elements 13.5 JSP DIRECTIVES JSP directives serve special processing information about the page to the JSP Server. A JSP directive affects the overall structure of the servlet class. They do not produce any output that is visible to the client. It usually has the following form : <%@ directive attribute = "value" %> Directives can have a number of attributes which you can list down as key-value pairs and separated by commas. The blanks between the @ symbol and the directive name, and between the last attribute and the closing %>, are optional. munotes.in
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Enterprise Java 140 There are three types of directive tag: Sr.No. Directive & Description 1 <%@ page ... %> Defines page-dependent attributes, such as scripting language, error page, and buffering requirements. 2 <%@ include ... %> Includes a file during the translation phase. 3 <%@ taglib ... %> Declares a tag library, containing custom actions, used in the page 13.5.1 Jsp Page Directive : The page direct ive is used to provide instructions to the container. These instructions pertain to the current JSP page. You may code page directives anywhere in your JSP page. By convention, page directives are coded at the top of the JSP page. Following is the basic sy ntax of the page directive : <%@ page attribute = "value" %> You can write the XML equivalent of the above syntax as follows − The following are the most common attributes associated with the page directive: Sr.No. Attribute and Example 1 language Defines the programming language used in the JSP page. Eg: <%@ page language="java"%> 2 import Specifies a list of packages or classes for use in the JSP as the Java import statement does for Java classes. Eg: <%@ page import="java.util.Date" %> 3 contentType Defines the character encoding scheme. Eg: <%@ page contentType=application/msword %> 4 extends Specifies a superclass that the generated servlet must extend. Eg: <%@ page extends = "somePackage.SomeClass" %> munotes.in
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Getting Started With Java Server Pages, Action Elements 141 5 isErrorPage Indicates if this JSP page is a URL specified by another JSP page's errorPage attribute. Eg: <%@ page isErrorPage="true" %> 6 session Specifies whether or not the JSP page participates in HTTP sessions. Eg: <%@ page session = "true" %> 7 info The info attribute lets you provide a description of the JSP. <%@ page info = "This is a JSP Page" %> Example: <%@ page contentType="text/html" %>
Today is: <%= new java.util.Date()%>
13.5.2 JSP Include Directive : The include directive is used to include a file during the translation phase. This directive tells the container to merge the content of other external files with the current JSP during the translation phase. You may code the include directives anywhere in your JSP page. The general usage form of this directive is as follows : <%@ include file = "relative url" > The filename in the include directive is actually a relative URL. If you just specify a filename with no associated pat h, the JSP compiler assumes that the file is in the same directory as your JSP. You can write the XML equivalent of the above syntax as follows : The file attribute : A page -relative or context -relative URI pat h to the file that will be included at the current position in the file. This attribute includes a static file ,merging its content with the including page before the combined result is converted to a JSP page implementation class. A page can contain multi ple include directives.
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Enterprise Java 142 Example:
<%@ include file="header.html" %> Today is: <%= java.util.Calendar.getInstance().getTime() %>
13.5.3 JSP Taglib Directive : The taglib directive declares that your JSP page use s a set of custom tags, identifies the location of the library, and provides means for identifying the custom tags in your JSP page. Custom Tags allow developers to hide complex server side code spec from web designers. A taglib directive in a JSP is a lin k to an XML document that describes a set of custom tag. This XML document also determine which Tag Handler class implements the action of each tag. The XML document names the tag library which holds the custom tags.The JSP engine uses this tag library to determine what to do when it comes across custom tags The taglib directive follows the syntax given below : <%@ taglib uri = "uri" prefix = "prefixOfTag" > You can write the XML equivalent of the above syntax as follows : The uri attribute : A Uniform Resource Identifier (URI) that identifies the Tag Library Descriptor ,which is used to uniquely name the set of custom tags and inform the server what to do with the specified tags. The prefix attribute : It defines the prefix string in : pair and informs the JSP container which bits of markup are custom tags. Example : <%@ taglib uri = "http://www.abc.com/mylib" prefix = "mytag" %>
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13.6 SCRIPTING ELEMENTS The scripting elements provides the ability to insert java code inside the jsp. There are three types of scripting elements: Declaration tag Expression tag Scriptlet tag These elements allow declaring variables and methods,including scrip ting code and evaluating an expression. 13.6.1 Declarations Tag : The JSP declaration tag is used to declare fields and methods. The code written inside the jsp declaration tag is placed outside the service() method of auto generated servlet. So it doesn't get memory at each request. The Syntax of JSP declaration tag is as follows: <%! Java variable and method declaration(s) %> You can write the XML equivalent of the above syntax as follows : Java variable and method declaration(s)
Example: <%! int num=0; public void count(){ { int num=10; } %>
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Enterprise Java 144 13.6.2 Scriptlets Tag: A scriptlet is a block of Java code spec that is executed at runtime. Scriptlets also known as JSP code fragments are embedded within <% …. %> tags. A Scriptlet can produce output passed through an output stream back to the client. The Syntax of JSP Scriptlets tag is as follows: <% Scriptlet code Spec %> You can write the XML equivalent of the above syntax as follows : Scriptle t code Spec
The following example program prints “Welcome to JSP” on the page. Example :
<% out.print("Welcome to jsp"); %>
13.6.3 Expressions Tag : It is mainly used to print the values of variable or method. The code placed within JSP expression tag is written to the output stream of the response. So you need not write out.print() to write data. After an expression is evaluated, the result is converted to a string and displayed. The Syntax of JSP Exp ression tag is as follows: <%= statement %> You can write the XML equivalent of the above syntax as follows : Statements : munotes.in
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Current Time: <%= java.util.Calendar.getInstance().getTime() %>
13.7 ACTION ELEMENTS JSP Action tags are used to control the flow between pages and to use Java Bean. JSP Action Elements are processed during the request processing phase as opposed to JSP directives which are processed during translation. Act ions use construct in XML syntax.It looks like a regular HTML tag and does not follow the <% … %> syntax. There are many JSP action tags or elements. Each JSP action tag is used to perform some specific tasks. JSP Action Tags Description jsp:forward forwards the request and response to another resource. jsp:include includes another resource. jsp:useBean creates or locates bean object. jsp:setProperty sets the value of property in bean object. jsp:getProperty prints the value of property of the bean. jsp:plugin embeds another components such as applet. jsp:param sets the parameter value. It is used in forward and include mostly. jsp:fallback can be used to print the message if plugin is working. It is used in jsp:plugin. 13.7.1 JSP: forward Action T ag: The forward action terminates the action of the current page and forwards the request to another resource such as a static page, another JSP page, or munotes.in
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Enterprise Java 146 a Java Servlet. It is same as forwarding to resources using RequestDispatcher interface in Servlets. Syntax: ”> ” value=””/>
page attribute : It is a string or an expression representing the relative URL of the component to which the request is forwarded. tag It is used to send one or more name=value pairs as parameters to a dynamic resource such as JSP,Servlets or other resources. Example without parameter Index.jsp
The forward JSP example
Example with parameter Index.jsp
Forwarding with Parameters
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13.7.2 JSP: Include Action Tag : The include action terminate s the action of the current page an d forwards the request to another resource such as a st atic page, another JSP page, or a Java Servlet. It is same a s forwarding to resources using RequestDispatcher interface in Servlets. Syntax: ” > ” value=””/>
page attribute : It is a string or an expression representing the relative URL of the component to which the request is forwarded. tag : It is used to send one or more name=value pairs as parameters to a dynamic resource such as JSP,Servlets or other resources. Example without parameter Index.jsp
Note: The difference between jsp include directive and include action tag is Include action includes response of a resource into the response of the JSP page Include directive includes resources in a JSP page at translation time. munotes.in
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13.7.3 jsp: useBean Action Tag: Before understanding what is ,we need to first understand JavaBean. JavaBean A J avaBean is a Java class that should follow the following conventions: It should have a no -arg constructor. It should be Serializable. It should provide methods to set and get the values of the properties, known as getter and setter methods. Example of Java Bean class : //Employee.java munotes.in
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Enterprise Java 150 package mypack; public class Employee implements java.io.Serializable{ private int id; private String name; public Employee(){} public void setId(int id){this.id=id;} public int getId(){return id;} public void setName(String name){this.name=name;} public String getName(){return name;} } To access the JavaBean class, we should use getter and setter methods. package mypack; public class Test{ public static void main(String args[]){ Employee e=new Employee();//object is created e.setName("Steve");//setting value to the object System.out.println(e.getName()); } } Action Tag : In JSP, is used to access the bean. instantiates an object of the class spec ified by the class and binds it to a variable with the name specified by ID.A new object is instantiated only if there is no existing one with the same ID and scope. Once a bean exists, its properties can be modified using or by using a scriptlet and calling a method explicitly. Existing properties can be read in a JSP or scriptlet by using . makes a JavaBean available to a JSP Page and ensures that the bean object is available for an appropriate scope specif ied in the element. Syntax of jsp:useBean action tag : class= "packageName.className" type= "packageName.className" munotes.in
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Getting Started With Java Server Pages, Action Elements 151 beanName="packageName.className | <%= expression >" >
Attributes and Usage of jsp:useBean action tag : 1. id: is used to identify the bean in the specified scope. 2. scope: represents the scope of the bean. It may be page, request, session or application. The default scope is page. o page: specifies th at you can use this bean within the JSP page. The default scope is page. o request: specifies that you can use this bean from any JSP page that processes the same request. It has wider scope than page. o session: specifies that you can use this bean from any J SP page in the same session whether processes the same request or not. It has wider scope than request. o application: specifies that you can use this bean from any JSP page in the same application. It has wider scope than session. 3. class: instantiates the sp ecified bean class (i.e. creates an object of the bean class) but it must have no -arg or no constructor and must not be abstract. 4. type: provides the bean a data type if the bean already exists in the scope. It is mainly used with class or beanName attribut e. If you use it without class or beanName, no bean is instantiated. 5. beanName: instantiates the bean using the java.beans.Beans.instantiate() method. Example: Calculator.java (a simple Bean class) package com.javatpoint; public class Calculator{ public int cube(int n){return n*n*n;} } index.jsp file <% int m=obj.cube(5); out.print("cube of 5 is "+m); %> munotes.in
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Enterprise Java 152 13.7.4 Action Tag : is used in conjuncti on with and sets the value of simple and indexed properties in a bean. The propert ies in a bean can be set either : At request time from parameters in the request object or At request time from an evaluated expression or From a specified strin g(or hard coded in the page) Syntax of jsp:setProperty Action Tag property="propertyName" param="parameterName" | property="propertyName" value="{ string | <%= expression %>}" /> Examp le: Example : Here, invokes getName() available in the Student class. 13.8 JSP GUI EXAMPLE Create a registration and login JSP application to register and authenticate the user based on username and password using JDBC. Initial. html : Sign up for New User
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Getting Started With Java Server Pages, Action Elements 153 Login for Existing User Index.html
Registration Page
Regis ter.jsp <%@page contentType="text/html" pageEncoding="UTF -8" import="java.sql.*"%>
13.9 SUMMARY JSP comments are ignored by the JSP engine when it translat es the JSP page into a Servlet. A JSP document can use either the traditional JSP style syntax or XML style JSP syntax within its source file. JSP Elements enclose the Java code in a JSP page and are categorized as follows: 1. Directives 2. Scripting Eleme nts 3. Action Elements JSP directives serve special processing information about the page to the JSP Server. The scripting elements provides the ability to insert java code inside the jsp. There are three types of scripting elements: 1. Declaration tag 2. Expression tag 3. Scriptlet tag JSP Action tags are used to control the flow between pages and to use Java Bean. munotes.in
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Getting Started With Java Server Pages, Action Elements 157 13.10 LIST OF REFERENCES 1. Java EE 7 for Beginners, Sharanam Shah, Vaishali Shah, First Edition, SPD Web References : 1. https://www.javatpoint.com 2. https://www.tutorialspoint.com 3. https://www.guru99.com 13.11 QUESTIONS Q1. What are the different ways of writing comments in Java? Q2. What are the various attributes used in the page directive?Explain with an example. Q3. What is the benefit of using taglib directive? Q4. What are the various Scripting elements available in JSP? Why are they used? Q5. What is the difference b etween include directive and include action tag? Q6. What is a JavaBean?Why is it used?Explain with an example. Q7. How is action tag used to set and access properties of a JavaBean? ***** munotes.in
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158 14 IMPLICIT OBJECTS, SCOPE AND EL EXPRESSIONS Unit Structure 14.0 Objectives 14.1 Implicit Objects 14.2 Scope 14.3 Character Quoting Conventions 14.4 Unified Expression Language (UEL) 14.4.1 Types of UEL 14.4.2 Method Expressions 14.4.3 Operators 14.5 Summary 14.6 List of References 14.7 Questions 14.0 OBJECTIVES After going through this chapter, you will: You will understand what are the various implicit objects in JSP Learn the various scope of objects in JSP Know what are character quoting co nventions and how to write them Learn what is Unified Expression Language and the benefits of using them 14.1 IMPLICIT OBJECTS Java Scripting Elements provide a great deal of power and flexibility to the developer to achieve dynamic website content deliver y.To achieve this, JSP engine exposes a number of internal Java objects to the developer. These objects do not need to be declared or instantiated by the developer but are provided by the JSP engine in its implementation and its execution. All implicit obj ects are available only to scriptlets or expressions.They are not available in declarations.
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Implicit Objects, Scope And EL Expressions 159 There are 9 implicit objects in JSP as follows: Object Type out JspWriter request HttpServletRequest response HttpServletResponse config ServletConfig application ServletContext session HttpSession pageContext PageContext page Object exception Throwable 1. out : This is the JspWriter object associated with the output stream of the response.For writing any data to the buffer, JSP provides an implicit object named out. It is the object of JspWriter. In case of servlet you need to write: PrintWriter out=response.getWriter(); But in JSP, you don't need to write this code as out is pre -defined. Example
<% out.print("This is Enterprise Java ”); %>
Here, we are simply printing the line “ This is Enterprise Java” as the response. 2. Request : The JSP request is an implicit object of type HttpServletRequest i.e. created for each jsp request by the web container. It can be used to get request information such as parameter, header information, remote address, server name, server port, content type, character encoding etc. It can also be used to set, get and remove attributes from the jsp request scope. Example index.html
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welcome.jsp <% String name=request.getParameter( "uname" ); out.print( "welcome "+name); %> 3. response : In JSP, response is an implicit object of type HttpServletResponse. The instance of HttpServletResponse is created by the web container for each jsp request. It can be used to add or manipulate response such as redirect response to another resource, send error etc. Let's see the example of respon se implicit object where we are redirecting the response to the Google. Example of response implicit object index.html
welcome.jsp <% response.sendRedirect("http://www.google.com"); %> 4) config : In JSP, config is an implicit object of type ServletConfig. This object can be used to get initialization parameter for a particular JSP page. The config object is created by the web container for each jsp page. Generally, it is used to get initialization parameter from the web.xml file. Example : index.html munotes.in
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Implicit Objects, Scope And EL Expressions 161 web.xml file sonoojaiswal /welcome.jsp dname sun.jdbc.odbc.JdbcOdbcDriver
sonoojaiswal /welcome
welcome.jsp : <% out.print("Welcome "+request.getParameter("uname")); String driver =config .getInitParameter("dname"); out.print("dri ver name is="+driver); %> 5) application : In JSP, application is an implicit object of type ServletContext. The instance of ServletContext is created only once by the web container when application or project is deployed on the server. This object can be used to get initialization parameter from configuaration file (web.xml). It can also be used to get, set or remove attribute from the application scope. t("driver nam Example: index.html
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Enterprise Java 162 sonoojaiswal /welcome.jsp
sonoojaiswal /welcome
dname sun.jdbc.odbc.JdbcOdbcDriver
welcome.jsp <% out.print("Welcome "+request.getParameter("unam e")); String driver=application.getInitParameter("dname"); out.prin e is="+driver); %> 6. session : In JSP, session is an implicit object of type HttpSession.The Java developer can use this object to set,get or remove attribute or to get session in formation. Example index.html
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Implicit Objects, Scope And EL Expressions 163 welcome.jsp
7. pageContext : In JSP, pageContext is an implicit object of type PageContext class.The pageContext object can be used to set,get or remove attribute from one of the following scopes: page request session application In JSP, page scope is the default scope. Example index.html
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welcome.jsp
<% String name =request.getParameter( "uname" ); out.print( "Welcome "+name); pageContext.setAttribute( "user" ,name,PageContext.SESSION_SCOPE); second jsp page %>
8) page : In JSP, page is an implicit object of type Object class.This object is assigned to the reference of auto generated servlet class. It is written as: Object page=this; For using this object it must be cast to Servlet type.For example: <% (HttpServlet)page.log("message"); %> Since, it is of type Object it is less used because you can use this object directly in jsp.For example: <% this.log( "message"); %> munotes.in
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Implicit Objects, Scope And EL Expressions 165 9) exception : In JSP, exception is an implicit object of type java.lang.Throwable class. This object can be used to print the exception. But it can only be used in error pages.It is better to learn it after page directive. Let's see a simple example: Example error.jsp <%@ page isErrorPage= "true" %>
Sorry following exception occured:<%= exception %>
14.2 SCOPE OF JSP OBJECTS The availability of a JSP object for use from a particular place of the application is defined as the scope of that JSP object. Every object created in a JSP page will have a scope. Object scope in JSP is segregated into four parts and they are page, request, session and application. Page Scope : Objects with page scope are acce ssible only within the page in which they're created. The data is valid only during the processing of the current response; once the response is sent back to the browser, the data is no longer valid. If the request is forwarded to another page or the brows er makes another request as a result of a redirect, the data is also lost. //Example of JSP Page Scope Request Scope : Objects with request scope are accessible from pages processing the same request in which they were created. Once the container has processed the request, the data is released. Even if the request is forwarded to another page, the data is still available though not if a redirect is required. //Example of JSP Request Scope Session Scope : Objects with session scope are accessible from pages processing requests that are in the same session as the one in which they were created. A session is the time users spend u sing the application, which ends when munotes.in
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Enterprise Java 166 they close their browser, when they go to another Web site, or when the application designer wants (after a logout, for instance). So, for example, when users log in, their username could be stored in the session and displayed on every page they access. This data lasts until they leave the Web site or log out. //Example of JSP Session Scope Application Scope : Objects with application scope are accessib le from JSP pages that reside in the same application. This creates a global object that's available to all pages. Application scope uses a single namespace, which means all your pages should be careful not to duplicate the names of application scope objec ts or change the values when they're likely to be read by another page (this is called thread safety). Application scope variables are typically created and populated when an application starts and then used as read -only for the rest of the application. //Example of JSP Application Scope /> 14.3 CHARACTER QUOTING CONVENTIONS Because certain character sequences are used t o represent start and stop tags, the developer sometimes needs to esc ape a character so the JSP engine does not interpret it as part of a special character sequence. In a scripting element, if the character needs %> needs to be used,escape the greater than sign with a backslash. <%String message=” This is the %/> message”; %> The backslash before the expression acts as an escape character and informs the JSP engine to not evaluate it. There are a number of cases where backslash needs to be used otherwise characters will be treated specially by the JSP engine. Escape Characters Description \’ A single quote in an attribute that uses single quote \” A double quote in an attribute that uses double quote \\ A backslash in an attribute that uses backslash munotes.in
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Implicit Objects, Scope And EL Expressions 167 %\> Escaping the scriptlet end tag with a backslash <\% Escaping the scriptlet start tag with a backslash \$ Escaping the $ sign with a backslash 14.4 UNIFIED EXPRESSION LANGUAGE (UEL) JSP Expression Language provides a way to simplify expressions. It is a simple language used for accessing implicit objects. Java classes a nd for manipulating collections in an elegant manner. It is the newly added feature in JSP technology version 2.0. The expression language also allows page authors to use simple expressions to dynamically read data from JavaBean components. Unified Express ion Language allows usage of simple expressions to perform the following tasks: Dynamically read application data stored in JavaBeans components, various data structures and implicit objects. Dynamically write data such user input into forms to JavaBeans components. Dynamically perform arithmetic operations. 14.4.1 Types o f Evaluation Expressions : Unified EL supports two types of evaluation expressions: Immediate and Deferred evaluation Immediate Evaluation: Immediate evaluation means that the expression i s evaluated and the result returned as soon as the page is first rendered. Syntax: ${} Here, Expression stands for valid expression. The following example shows a tag whose value attribute references an immediate evaluation expression that upda tes the quantity of books retrieved from the backing bean named catalog: Deferred Evaluation: Deferred evaluation means that the technology using the expression language can use its own machinery to evaluate the expression sometime later during the page’s lifecycle, whenever it is appropriate to do so. munotes.in
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Enterprise Java 168 Syntax: #{} Here, Expression stands for valid expression. Because of its multiphase lifecycle, JavaServer Faces technology uses mostly deferred ev aluation expressions. During the lifecycle, component events are handled, data is validated, and other tasks are performed in a particular order. Therefore, a JavaServer Faces implementation must defer evaluation of expressions until the appropriate point in the lifecycle. Other technologies using the EL might have different reasons for using deferred expressions. The following example shows a JavaServer Faces h:inputText tag, which represents a field component into which a user enters a value. The h:inputT ext tag’s value attribute references a deferred evaluation expression that points to the name property of the customer bean: 14.4.2 Value Expressions : The unified EL provides two types of value expressions : Rvalue Expressions: Can only read data, but cannot write data. Expressions that use deferred valuation syntax are always rvalue expressions. Lvalue Expressions: Can read and write data. Expressions that uses deferred evaluation syntax can act as both Rv alue and Lvalue expressions. Consider the following two value expressions: ${customer.name} #{customer.name} The former uses immediate evaluation syntax, whereas the latter uses deferred evaluation syntax. The first expression accesses the name property, g ets its value, and passes the value to the tag handler. With the second expression, the tag handler can defer the expression evaluation to a later time in the page lifecycle if the technology using this tag allows. In the case of JavaServer Faces technolog y, the latter tag’s expression is evaluated immediately during an initial request for the page. During a postback request, this expression can be used to set the value of the name property with user input. munotes.in
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Implicit Objects, Scope And EL Expressions 169 14.4.3 Method Expressions : EL also supports defer red method expressions. A method expression is used to refer to a public method of a bean and has the same syntax as an lvalue expression. A JSF component element usesmethod expressions, which in turn invokes method that do some process on behalf of the co mponent element. For standard components, these methods are necessary for handling events that the components generates as well as validating component data. Example Solution: Validator=”#{customer .validateFirstname}”/> Explanation: The validator attribute of references validateFirstnameid() owned by a bean called customer. specifies that validateFirstName() should be invoked during the validation process phase of the JSF lifecycle. Because a method can be invoked during different phases of the lifecycle, method expressions must always use the deferred evaluation syntax. 14.4.4 Operators : EL the following operators, most of which are usual operators available in Java: 1. Arithmetic Operators : The following are the arithmetic operators: +Addition [Binary]:(subtraction) :Multiplication / or div:Division % or mod:modulo[remainder] -[unary]:Negation of a value Example 1. ${5*5+4} 2. ${1.2E4+1.4} munotes.in
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Enterprise Java 170 3. ${10 mod 4} 4. ${3 div 4} Output: 1. 29 2. 12001.4 3. 2 4. 0.75 2. Logical Operators : The following are the logical operators: && or AND: Test for logical AND || or OR : Test for logical OR ! or NOT :Unary Boolean complement Example <%-- Evaluates if variable is not empty --%> ${!empty} 3. Relational Operators : The following are the relational operators: == or eq :Test for equality != or ne: :Test for inequality < or lt: Test for less than > or gt : Test for greater than <= or le : Test for less than or equal >= or ge : Test for greater than or equal Example: ${10>3} ${1>8} ${10 le 3}
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Implicit Objects, Scope And EL Expressions 171 4. Conditional Operators : The following is the syntax for conditional operators: Condition ? If true :If false Solution A?B:C Here B is evaluated if A is true else is evaluated if A is false 5. The [Dot] Operator : It is a shorthand for calling a JavaBeans property accessor for the property whose name is on the right side of the operator. Solution ${pageContext.servletContext.servletContextName} 6. The [] Operator : Is is used for polymorphic indexing, which can be used for indexing collections including Maps,Lists and Arrays. The value inside the brackets is used as a key into a map or as a List or array index. Example: ${colors[5]} ${colors[1]>colors[6]} 7. The empty operator : It is a prefix operator that is used to determine if a value is null or empty. Example ${empty Name} This expression returns true if Name refers a null value. 14.4.5 JSP EL IMPLICIT OBJECTS : The JSP expression language supports the following implicit objects : Sr. No. Implicit object & Description 1 pageScope Scoped variables from page scope 2 requestScope Scoped variables from request scope 3 sessionScope Scoped variables from session scope munotes.in
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Enterprise Java 172 4 applicationScope Scoped variables from application scope 5 param Request parameters as strings 6 paramValues Request parameters as collections of strings 7 header HTTP request headers as strings 8 headerValues HTTP request headers as collections of strings 9 initParam Context -initialization parameters 10 cookie Cookie values 11 pageContext The JSP PageContext object for the current page 14.5 SUMMARY JSP provides a number of implicit objects which need not be declared or instantiated by the developer. Implicit objects are available only to scriptlets or expres sions.They are not available in declarations. JSP objects have 4 scopes: page,request,session and application The escape character backslash can be used to inform the JSP engine not to evaluate certain expressions. Unified Expression Language provides a wa y to simplify expressions and can be used for accessing implicit objects. UEL supports both immediate and deferred evaluation. UEL also supports various operators and can be used to call methods. 14.6 LIST OF REFERENCES Java EE 7 for Beginners, Sharanam S hah, Vaishali Shah, First Edition, SPD Web References : 1. https://www.javatpoint.com 2. https://www.java -samples.com munotes.in
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Implicit Objects, Scope And EL Expressions 173 14.7 QUESTIONS Q1. List the various implicit objects in JSP. Q2. Explain the scope of JSP objects. Q3. What is Immediate and Deferred Evaluation? Explain with an example. Q4. Write a note on character quoting conventions. Q5. Explain Method Expressions in short. Q6. What are the various operators supported by JSP EL? *****
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174 15 JSP STANDARD TAG LIBRARIES Unit Structure 15.0 Objectives 15.1 Introduction to Java Server Pages Standard Tag Libraries 15.2 Disadvantages of JSP Scriptlet Tags 15.3 Advantages of JSTL 15.4 Disadvantages of JSTL 15.5 How is JSTL different from Sc riptlets? 15.6 Types of Tag Libraries 15.6.1 Core Tag Library 15.6.2 Functions Tag Library 15.6.3 Database/SQL Tag Library 15.6.4 Formatting Tag Library 15.6.5 XML Tag Library 15.7 Summary 15.8 List of References 15.9 Questions 15.0 OBJECTIVES After go ing through this chapter, you will: Understand what is Java Server Pages Tag Libraries Understand the advantages and disadvantages of JSTL Learn what are the issues of using Scriptlet Tags Learn the various types of Tag Libraries and available tags 15.1 IN TRODUCTION TO JSP STANDARD TAG LIBRARIES JSTL was introduced to allow JSP programming developers to create web applications using tags rather than scriptlets (Java code). It is a collection of useful JSP tags which encapsulates the core functionality commo n to many JSP applications. JSTL does nearly everything that a regular scriptlet does. JSTL has support for common, structural tasks such as iteration and conditionals, tags for manipulating XML documents, internationalization tags, and SQL tags. It also provides a framework for integrating the existing custom tags with the JSTL tags. munotes.in
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JSP Standard Tag Libraries 175 15.2 DISADVANTAGES OF JSP SCRIPTLET TAGS 1. The Java code embedded within the Scriptlet looks ugly and inconsistent with the HTML tags. 2. The developer who does not know Java act ually cannot modify the embedded Java code. Thus, this disadvantage nullifies the major benefit of JSP, which is the empowerment of designers and business people to update page content. 3. The Java code embedded within the scriptlets cannot be re -used by another JSP Pages. So, the common logic code gets duplicated in multiple JSP pages. 4. Accessing values from HTTP request and sessions needs to be specifically typecasted to the object’s class, which should be known to the JSP by importing or fully qualifying the class name. 15.3 ADVANTAGES OF JSTL 1. JSTL tags are XML based tags, they cleanly and consistently blend into a page’s HTML markup tags. 2. JSTL tags are easier to use effectively as they do not require any knowledge of Java programming. 3. JSTL tags can be reused in various pages unlike scriptlets which needs to be repeated everywhere. 4. JSTL tags can reference objects in Request and Session objects without knowing the object’s type with no typecasting required. 5. JSTL makes use of UEL which makes it easier to call th e getter and setter methods on Java objects. 15.4 DISADVANTAGES OF JSTL 1. JSTL increases the processing burden on the server. Java scriptlet and the tag libraries both are compiled into a servlet, whi ch is then executed by the Servlet engine. Java code in sc riptlets is pretty much just copied into Servlets but on the other hand , JSTL tags casue much more code to be added to the Servlet. 2. JSTL provides a powerful set of reusable libraries to JSP developers but JSTL cannot do everything that the Java code spec c an do. 15.5 HOW IS JSTL DIFFERENT FROM SCRIPTLETS An example of scriptlet -based programming, which counts to 10, is shown here: munotes.in
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Count to 10 in JSP scriptlet
<% for(int i=1;i<=10;i++) { %> <%=i%>
<% } %>
As you can see from the preceding example, using scriptlet code produces page source code that contains a mix of HTML tags and Java statements making the code looking non -consistent. Consider the following example, which shows how to coun t from 1 to 10 using JSTL rather than scriptlet code. <%@ taglib uri="http://java.sun.com/jstl/core" prefix="c" %>
Count to 10 Example (using JSTL)
When you examine the preceding source code, you can see that the JSP page consists entirely of tags thus bringing consistency and uniformity to the code. 15.6 TYPES OF JSTL TAG LIBRARIES JSTL Tag L ibraries can be broken down into specific functional areas belonging to an application. JSTL is composed of five tag libraries: munotes.in
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JSP Standard Tag Libraries 177 Core Tag Library Functions Tag Library Database/SQL Tag Library Formatting Tag Library XML Tag Library Let’s understand the vari ous tags under each of the above Tag Libraries. 15.6.1 Core Tag Library : The Core Tag Library contains tags that are essential to nearly any Web application. Examples of core tag libraries are looping, evaluation of expression and basic input and output. The URI of the Core Tag Library is “http://java.sun.com/jsp/jstl/core ” and prefix is c. The syntax used for including JSTL Core tags library in your JSP is: <%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %> The Core Tag Library consists of four distinct functional sections: A) General - Purpose Actions : These actions allow adding and removing variables ,displaying variable values and enclosing a group of tags within a try -catch block. 1. The tag displays the result of an expression. This is almost similar to the way <%= %> works. Example: This will print Hello World as a response. 2. The tag sets the result of an expression ev aluation in a 'scope'. Example This will set a variable names session with the value 2000. 3. The tag removes a scoped variable (from a particular scope, if specified). munotes.in
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Enterprise Java 178 Example: This will remove the variable named salary. 4. The tag catches any Throwable that occurs in its body and optionally exposes it. Example: <% int x = 5/0;%>
This code block will catch ArithmeticException. B) Conditional Actions Or Flow Control Statements: Conditi onal Actions are used for conditional processing within a JSP page. 1. The tag evaluates an expression and displays its body content only if the expression evaluates to t rue. Example :
My salary is:
This will print the statement within tag if the condition mentioned in test evaluates to true. 2. ,, : The works like a Java switch statement in that it lets you choose between a number of alternatives. Where the switch statement has case statements, the tag has tags. Just as a switch statement has the default clause to specify a def ault action, has as the default clause. Example: munotes.in
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JSP Standard Tag Libraries 179 ${"number1 is le ss than number2"}
${"number1 is less than equal to number2"}
Example ${"number1 is less than number2"}
${"number1 is less than eq ual to number2"}
C) Iterator Actions: Iterator Actions simplify iteration through collection of objects. 1. The tag is a commonly used tag because it repeats the nested body content for fixed number of times or over collection. Example Item
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Enterprise Java 180 This will print the values from 1 to 5. 2. The tag iterates over tokens which is separated by the supplied delimeters. It is used for break a string into tokens and iterate through each of t he tokens to generate output. This tag has similar attributes as tag except one additional attributes delims which is used for specifying the characters to be used as delimiters. Example
This will print the names as separate tokens. D.) URL RELATED ACTIONS : These actions are used to import resources, redirect HTTP responses ,create URLs or encode a request of parameters. 1. The < c:redirect > tag redirects the browser to a new URL. Example : This will redirect to abc.com 2. The < c:url > tag creates a URL with optional query parameter. It is used for url encoding or url formatting. This tag automatically performs the URL rewriting operation. Example : 3. The < c:param > tag add the parameter in a containing 'import' tag's URL. Example : munotes.in
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JSP Standard Tag Libraries 181 15.6.2 Functions Tag Library: The Functions Tag Library provides a number of standard functions, most of these functions are common string manipulation functions. The URI of the Functions Tag Library is “http://java.sun.com/jsp/ jstl/functions” and prefix is fn. The syntax used for including JSTL Functions tags library in your JSP is: <%@ taglib uri="http://java.sun.com/jsp/jstl/functions" prefix="fn" %> Tag Explanation Example Output fn:contains() It is used to test if an input string containing the specified substring in a program. ${fn:contains(‘Java’,’av’ )} True fn:containsIgnoreCase() It is used to test if an input string contains the specified substring as a case insensitive way. ${fn:containsIgnoreCase(‘Java’, 'AV')} True fn:endsWith() It is used to test if an input string ends with the specified suffix. ${fn:endsWith(‘JSP Program’, 'Program')} True fn:escapeXml() It escapes the characters that would be interpreted as XML markup. ${fn:escapeXml(‘It is second String.’)} It is second String. fn:indexOf() It returns an index within a string of first occurrence of a specified substring. ${fn:indexOf(‘Hello World’,’ ‘Hello’)} 0 fn:trim() It removes the blank spaces from both the ends of a string. ${fn:trim(Welcome to JSP programming )} Welcome to JSP programming fn:startsWith() It is used for checking whether the given string is started with a particular string value. ${fn:endsWith(‘JSP Program’, 'JSP')} True fn:split() It splits the string into an array of substrings. ${fn:split(Welcome-to-JSP-Programming, '-')} Welcome To JSP Programming fn:toLowerCase() It converts all the characters of a string to lower case. ${fn:toLowerCase("HELLO")} hello munotes.in
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Enterprise Java 182 fn:toUpperCase() It converts all the characters of a string to upper case. ${fn:toLowerCase("hello")} HELLO fn:substring() It returns the subset of a string according to the given start and end position. ${fn:substring("This is the first string.", 5, 17)} is the first fn:substringAfter() It returns the subset of string after a specific substring. ${fn:substringAfter(“Chris Kevin”, "Chris")} Kevin fn:substringBefore() It returns the subset of string before a specific substring. ${fn:substringBefore(“Chris Kevin”, "Kevin")} Chris fn:length() It returns the number of characters inside a string, or the number of items in a collection. ${fn:length(“Hello”)} 5 fn:replace() It replaces all the occurrence of a string with another string sequence. ${fn:replace(“Chris Kevin”, "Chris", "Steve")} Steve Kevin 15.6.3 Database/ SQL Tag Library : The SQL tag library allows the tag to interact with RDBMSs (Relational Databases) such as Microsoft SQL Server, mySQL, or Oracle. The URI of the SQL Tag Library i s “http://java.sun.com/jsp/jstl/sql” and prefix is sql. The syntax used for including JSTL Database tags library in your JSP is: <%@ taglib uri="http://java.sun.com/jsp/jstl/sql" prefix="sql" %> 1) The tag is used to create the data source variable directly from JSP and it is stored inside a scoped variable. It can be used as input for other database actions. Example : user="root" password="1234"/> This code is used for setting the connection with database server. munotes.in
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JSP Standard Tag Libraries 183 2) The tag is used for executing the SQL query defined in its sql attribute or the body. It is used to execute an SQL SELECT statement and saves the result in scoped variable. Example: SELECT * from Students;
3) The tag is used for executing the SQL DML query defined in its sql attribute or in the tag bod y. It may be SQL UPDATE, INSERT or DELETE statements. Example: INSERT INTO Students VALUES (154,’Chris’, 'Kevin', 25);
4. The tag sets the parameter value in SQL state ment. It is used as nested tag for and to provide the value in SQL query parameter. If null value is provided, the value is set at SQL NULL for value attribute. Example: DELETE FROM Students WHERE Id = ?
5. The is used to set the specified date for SQL query parameter. It is used as nested tag for and < sql:query> to provide the date and time value for SQL query parameter. If null value is provided, the value is set at SQL NULL. munotes.in
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Enterprise Java 184 Example: <% Date DoB = new Date("2000/10/16"); int studentId = 151; %> UPDATE Student SET dob = ? WHERE Id = ?
6. The tag is used for transaction management. It is used to group multiple into common transaction. If you group multiple SQL queries in a single transaction, database is hit only once. It is used for ensuring that the database modifications are performed by the nested actions which can be either rolled back or committed. Example: <% Date DoB = new Date("2000/10/16"); int studentId = 151; %> UPDATE Student SET First_Name = ‘Ann’ WHERE Id = 150
UPDATE Student SET Last_Name= ‘Seema’ WHERE Id = 153
INSERT INTO Student VALUES (101,'Kate', 'David', '2021/10/7');
15.6.4 Formatting Ta g Library : The formatting tags provide support for message formatting, number and date formatting etc. munotes.in
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JSP Standard Tag Libraries 185 The url for the formatting tags is http://java.sun.com/jsp/jstl/fmt and prefix is fmt . The syntax used for including JSTL FORMATTING tags library in your JSP is: <%@ taglib uri="http://java.sun.com/jsp/jstl/fmt" prefix="fmt" %> 1. The tag is used to Parses the string representation of a currency, percentage, or number. It is based on the customized formatting pattern. Example : <%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %> <%@ taglib prefix="fmt" uri="http://java.sun.com/jsp/jstl/fmt" %>
Amo unt is:
Amount is:
2. The tag is used to format the numerical value using the specific format or precision. It is used to format percentages, currencies, and numbers according to the customized formatting pattern. Example : <%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core"%> <%@ taglib prefix="fmt" uri="http://java.sun.com/jsp/jstl/fmt"%>
Formatting of Number:
Formatted Number -1:
Formatted Number -2:
Formatted Number -3:
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Enterprise Java 186
Formatted Number -4:
Formatted Number -5:
Formatted Number -6:
3. The tag parses the string representation of a time and date. It is used to format the time and date according to a customized formatting pattern. Example : <%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %> <%@ taglib prefix="fm t" uri="http://java.sun.com/jsp/jstl/fmt" %>
fmt:parseDate Tag
Parsed Date:
4. The tag loads the resource bundle which is used by its tag body. This tag will make the specified bundle available for all tags that occurs between t he boundary of and tags. It is used to create the ResourceBundle objects which will be used by their tag body. munotes.in
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JSP Standard Tag Libraries 187 Let us define the default resource bundle Simple.java as follows: package com.javatpoint; import java.util.ListResou rceBundle; public class Simple extends ListResourceBundle { public Object[][] getContents() { return contents; } static final Object[][] contents = { { "colour.Violet", "Violet" }, { "colour.Indigo", "Indigo" }, { "colour.Blue", "Blue" }, }; } Now you can use the below JSTL tags to display the three colors as follows: <%@ taglib uri="http://java.sun.com/jsp/jstl/fmt" prefix="fmt" %>
fmt:bundle Tag
Output: 1. Violet 2. Indigo 3. Blue 5. The t ag store the time zone inside a time zone configuration variable. It is used for copy a time zone object inside a specified scope variable. Let's see the simple example to understand the formatting tag: munotes.in
Date and Time in Indian Standard Time(IST) Zone: e="long" />
Date and Time in GMT - 10 time Zone: type="both" timeS tyle="long" dateStyle="long" />
6. and The tag is used to load the resource bundle and store their value in the bundle configuration variable or the name scope variable. It is used for creating the ResourceBundle object which will be used by tag body. The tag is used for displaying an internationalized message. It maps the key of localized message to return the value using a resource bundle specified in the bundle attribute . Let us define the default resource bundle Main.java as follows: package com.javatpoint; import java.util.ListResourceBundle; public class Main extends ListResourceBundle { public Object[][] getContents() { return contents; } static final Object[][] contents = { { "vegetable.Potato", "Potato" }, { "vegetable.Tomato", "Tomato" }, { "vegetable.Carrot", "Carrot" }, }; } munotes.in
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JSP Standard Tag Libraries 189 Now, compile the above class as Main.class and make it available in CLASSPATH of your Web application folder. Now you ca n use the below JSTL tags to display the three vegetables as follows: <%@ taglib uri="http://java.sun.com/jsp/jstl/fmt" prefix="fmt" %>
fmt:setBundle Tag
15.6.5 XML TAG LIBRARY : The JSTL XML tags are used for providing a JSP -centric way of manipulating and creating XML documents. The xml tags provide flow control, transformation etc. The url for the xml tags is http://java.sun.com/jsp/jstl/xml and prefix is x. The JSTL XML tag library h as custom tags used for interacting with XML data. The syntax used for including JSTL XML tags library in your JSP is: <%@ taglib uri="http://java.sun.com/jsp/jstl/xml" prefix="x" %> 1. and tag The tag is used for displaying the result of an xml Path expression and writes the result to JSP writer object. The tag is used for parse the XML data specified either in the tag body or an attribute. It is used for parse the xml content and the result will stored inside specifie d variable. Let's see the simple example to understand the xml and tag: <%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %> <%@ taglib prefix="x" uri="http://java.sun.com/jsp/jstl/xml" %>
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Enterprise Java 190
XML Tags
Vegetable Information:
onion 40/kg
Potato 30/kg
Tomato 90/kg
Name of the vegetable is:
Price of the Potato is:
2. The tag is used to set a variable with the value of an XPath expression. It is used to store the resul t of xml path expression in a scoped variable. Example munotes.in
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JSP Standard Tag Libraries 191 3. , , The tag is a conditional tag that establish a context for mutually exclusive conditional operations. It works like a Java switch statement in which we choose between a numbers of alternatives. The is subtag of that will include its body if the condition evaluated be 'true'. The is also subtag of < x:choose> it follows tags and runs only if all the prior condition evaluated is 'false'. The and works like if -else statement. But it must be placed inside tag. Example : <%@ taglib prefix="c" uri="http://java.sun. com/jsp/jstl/core" %> <%@ taglib prefix="x" uri="http://java.sun.com/jsp/jstl/xml" %>
x:choose Tag
Books Information:
Three mistak es of my life Chetan Bhagat 200
Tomorrow land Brad Bird 2000
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Enterprise Java 192 Book is written by Chetan bhagat
Book is written by Brad Bird
The author is unknown...
Output : Books Information: Book is written by Brad Bird 4. The tag is used for evaluating the test XPath expression. It is a simple conditional ta g which is used for evaluating its body if the supplied condition is true. Example : Vegetables prices are very low.
15.7 SUMMARY JSTL allows JSP programming developers to create web appli cations using tags rather than scriptlets (Java code). 1. JSTL tags are XML based tags, they cleanly and consistently blend into a page’s HTML markup tags. 2. JSTL makes use of UEL which makes it easier to call the getter and setter methods on Java objects. 3. JSTL increases the processing burden on the server. 4. JSTL is composed of five tag libraries: a. Core Tag Library munotes.in
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JSP Standard Tag Libraries 193 b. Functions Tag Library c. Database/SQL Tag Library d. Formatting Tag Library e. XML Tag Library 15.8 LIST OF REFERENCES 1. Java EE 7 for Beginners, Sharanam Shah, V aishali Shah, First Edition, SPD Web References : 1. https://www.tutorialspoint.com 2. https://www.javatpoint.com 15.9 QUESTIONS Q1. What are the various advantages of usin g JSTL over scriptlets? Q2. What are the various disadvantages of using JSTL? Q3. Explain , and tags with example. Q4. Explain how database connection can be established and queries can be executed using Database Tag Library. Q5. Explain any 5 tags of Formatting Tag Library. Q6. What are the various conditional and iteration tags in Core Tag Library? ***** munotes.in
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194 UNIT IV 16 INTRODUCTION TO ENTERPRISE JAVABEANS Unit Structure 16.0 Objectives 16.1 Introduction 16.1.1 When to use Enterprise Java Beans? 16.1.2 Advantages of Enterprise Java Beans 16.1.3 Disadvantages of Enterprise Java Beans 16.2 Architecture of EJB 16.2.1 Enterprise bean server 16.2.2 Enterprise bean container 16.2.3 Enterprise bean 16.2.4 Enterprise bean clients 16.3 Container and its types 16.4 Types of Enterprise Java Beans 16.4.1 Session Bean 16.4.2 Entity Bean 16.4.3 Message Driven Beans 16.5 Accessing Enterprise Bean’ 16.6 How to use Beans in Clients 16.6.1 Remote Clients 16.6.2 Local Clients 16.6.3 Characteristics of Remote clients 16.6.4 Characteristics of Local clients 16.7 Summary 16.8 Refe rences 16.9 Unit End Questions 16.0 OBJECTIVES After going through this chapter, you will be able to: • Understand use, advantage, disadvantage of EJB • Analysis architecture of EJB. • Type of Java Beans • How to access and use beans in clients munotes.in
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Introduction to Enterprise Javabeans 195 16.1 INTROD UCTION What is EJB?: EJB stands for Enterprise Java Bean. An Enterprise Java Bean is in its basic form any POJO (Plain Old Java Object) that is registered with the container in which it is deployed. Enterprise Java Beans are deployed into an EJB container . The EJB container is governed by the EJB specification. EJB (Enterprise Java Bean) is used to develop scalable, robust and secured enterprise applications in java. EJB is a server -side software element that summarizes business logic of an application. Enterprise Java Beans (EJB) is a development architecture for building highly scalable and robust enterprise level applications to be deployed on J2EE compliant Application Server such as JBOSS, Web Logic etc. EJB 3.0 is being a great shift from EJB 2.0 and makes development of EJB based applications quite easy. EJB stands for Enterprise Java Beans. EJB is an essential part of a J2EE platform. J2EE platform has component based architecture to provide multi -tiered, distributed and highly transactional features to enterprise level applications. EJB provides an architecture to develop and deploy component based enterprise applications considering robustness, high scalability, and high performance. An EJB application can be deployed on any of the application serve r compliant with the J2EE 1.3 standard specification. 16.1.1 When to use Enterprise Java Beans?: • Application needs Remote Access: In other words, it is distributed. • Application needs to be scalable: EJB applications supports load balancing, clustering and fail -over. • Application needs encapsulated business logic: EJB application is differentiated from demonstration and persistent layer. 16.1.2 Advantages of Enterprise Java Beans: • Interoperability: EJB architecture is mapped to standard CORBA.EJB make it work with components developed in different language like VC++ and CORBA. The EJB client view interface serves as well -defined integration point between components built using different programming languages. munotes.in
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Enterprise Java 196 • One business logic having many presentat ion logic: EJB performs a separation between business logic and presentation logic. This separation makes it possible to develop multiple presentation logic for the same business process. • Complete Focus only on Business Logic: This allows the server vend or to concentrate on system level functionalities, while the developer can concentrate more on only the business logic for the domain specific applications. Developer need not code for these hardcore services. The results of application get more quickly. • Server -Side Write Once, Run Anywhere: EJB uses java language which is portable across multiple platforms. They can be developed once and then deployed multiple platforms without recompilation or source code modification. • EJB provides Distributed Transac tion support: EJB provides transparency for distributed transactions. This means that a client can begin a transaction and then invoke methods on Beans present within two different servers, running on different machines, platforms or JVM. • It provides of vendor specific enhancements: Since the EJB specification provides a lot of flexibility for the vendors to create their own enhancements, the EJB environment may end being feature rich. 16.1.3 Disadvantages of Enterprise Java Beans: • The EJB specificatio n is an inconvenient tool because of its vast documentation and complex nature. A good developer must take the time to read and study the EJB specification - even if some information is irrelevant to EJB code writing and deployment. • EJB requires more dev elopment and debugging resources than basic Java coding, as it is difficult to determine whether a bug is inside the code or EJB container. • EJB implementation is complex. For example, a developer may write 10 or more files (versus one) for a simple appli cation, such as printing simple text like "hello world." • EJB specification changes result in obsolete code. Thus, making code compatible with a new EJB container requires extra effort and higher costs. munotes.in
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Introduction to Enterprise Javabeans 197 16.2 ARCHITECTURE OF EJB EJB Architecture: The Enter prise JavaBeans (EJB) component architecture is designed to enable enterprises to build scalable, secure, multiplatform, business - critical applications as reusable, server -side components. EJB architecture is at the heart of the Java 2 platform, Enterprise Edition (J2EE). With the growth of the Web and the Internet, more and more enterprise applications are now Web based, including both intranet and extranet applications.
Together, the J2EE and EJB architectures provide superior support for Web -based ent erprise applications. EJB architecture is composed of: 17 Enterprise bean server 18 Enterprise bean container 19 Enterprise bean 20 Enterprise bean clients 16.2.1 Enterprise Bean Server: An EJB server is a component transaction server. It supports the EJB server side component model for developing and deploying distributed enterprise level applications in multi -tiered environment. The key responsibilities of an Application Server are: • Management API • Process and thread management • Database connection po oling and caching • System Resources management munotes.in
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Enterprise Java 198 16.2.2 Enterprise Bean Container: The EJB container is one of the logical constructs which makes up the Full Java EE profile. An EJB container manages the enterprise beans contained within it. EJB server prov ides one or more containers. From our architecture diagram, we saw that the EJB container construct is the second outmost construct of the architecture. Furthermore, its key responsibilities are: • It provides a runtime environment for Enterprise Java Bean s • It provides persistence management • It is responsible for the Lifecycle management of EJBs • It is in charge of ensuring that all EJBs are secured 16.2.3 Enterprise Bean: Enterprise Beans are reu sable modules code that combine related tasks into well -defined interface. These enterprise bean EJB components contain the methods that execute business login and access data sources. Business component developed using EJB architecture are called as Enterprise Beans. EJBS are server -side components for encaps ulating application's business logic. An EJB can offer specific enterprise service either alone or in conjunction with other EJBs. 16.2.4 Enterprise Bean Clients: There are two types of client view: • Remote Client View • Local Client View 1. Remote Client View: The remote client view specification became available beginning with EJB 1.1. The remote client view of an enterprise bean is location independent. A client running in the same JVM as a bean instance uses the same API to access the bean as a client running in a different JVM on the same or different machine. Remote interface: The remote interface specifies the remote business methods that a client can call on an enterprise bean. Remote home interface: The remote home interface specifies the methods u sed by remote clients for locating, creating, and removing instances of enterprise bean classes. munotes.in
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Introduction to Enterprise Javabeans 199 2. Local Client View: Unlike the remote client view, the local client view of a bean is location dependent. Local client view access to an enterprise bean req uires both the local client and the enterprise bean that provides the local client view to be in the same JVM. The local client view therefore does not provide the location transparency provided by the remote client view. Local interfaces and local home in terfaces provide support for lightweight access from enterprise bean that are local clients. Session and entity beans can be tightly couple with their clients, allowing access without the overhead typically associated with remote method calls. The local cl ient view specification is available in EJB 2.0 or later. Local interface: The local interface is a lightweight version of the remote interface, but for local clients. It includes business logic methods that can be called by a local client. Local home inte rface: The local home interface specifies the methods used by local clients for locating, creating, and removing instances of enterprise bean classes. 16.3 CONTAINER AND ITS TYPES EJB Containers: Enterprise beans (EJB components) are Java programming lang uage server components that contain business logic. The EJB container provides local and remote access to enterprise beans. The container is responsible for creating the enterprise bean, binding the enterprise bean to the naming service so other applicatio n components can access the enterprise bean, ensuring only authorized clients have access to the enterprise bean’s methods, saving the bean’s state to persistent storage, caching the state of the bean, and activating or passivating the bean when necessary. It is responsible for all the operations of the EJB applications. The container acts as an intermediary action between the business logic of the bean and the rest of the world of the enterprise application. One or more EJB modules can be installed within a single EJB container. The role of EJB container is to perform transactional actions such as, munotes.in
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Enterprise Java 200 1. Starting a transaction. 2. Rollback a transaction or commit a transaction. 3. Managing various connection pools for the database resources. 4. Bean’s inst ance variables with corresponding data items which are stored in a database will be synchronized. The four types of container that J2EE supports: 1. EJB container 2. Web Container 3. Application client container 4. Applet client container 1) EJB Contain er: An EJB container will provide the runtime environment for EJB applications within the application server. It is responsible for all the operations of the EJB applications. The container acts as an intermediary action between the business logic of the b ean and the rest of the world of the enterprise application. One or more EJB modules can be installed within a single EJB container. The role of EJB container is to perform transactional actions such as, 1. Starting a transaction. 2. Rollback a transacti on or commit a transaction. 3. Managing various connection pools for the database resources. 4. Bean’s instance variables with corresponding data items which are stored in a database will be synchronized. 2) Web Container: A web container implements a we b component such as servlet container. A servlet container supports the operations of a servlet. It supports the web server operations and the client java operations such as JRE,maps the URL specific requests into servlet requests. The servlet cotainers ha ve the ability to dynamically add or remove servlets from the system. munotes.in
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Introduction to Enterprise Javabeans 201 Individual servlets will get registered by the servlet container. The servlet API is provided by different vendors for a specific servlet standard. 3) Application Client Container: An ap plication client container includes set of java classes, libraries and the set of files that are needed and distributed among various java client applications which executes on their own JVMs. The ACC is responsible for managing the applications execution by providing all the system services that are needed for the execution of java client programs. It is light -weighted and communicates with different application servers. 4) Applet client container: Like application client container, applet container execut es the client applications. The difference is an applet executes the application in a separate browser. They execute on their own JVMs. It supports the applet programming model. JEE client may use java plug -in to provide the required environment that execu tes the applet. Develope r classes vs. container classes: The developer classes are the classes that are authored by the developers The container classes are the classes which supports the container to manage the container specific functionality. 16.4 TYPES OF ENTERPRISE JAVA BEANS munotes.in
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Enterprise Java 202 The EJB 2.0 specification defines three types of Enterprise JavaBeans: the session bean, the entity bean, and the message -driven bean. Session beans contain business -processing logic. Entity beans contain data-processing logic. Message -driven beans allow clients to asynchronously invoke business logic. 16.4.1 Session Bean : Session beans are Java beans which encapsulate the business logic in a centralized and reusable manner such that it can be used by a number of clients. A ses sion bean objects are short -lived. Are not persistent in a database. They can be stateful or stateless. Execute for a single client. Can be transaction aware. As its name suggests, session beans implement a conversation between a client and the server side . Session beans execute a particular business task on behalf of a single client during a single session. They implement business logic such as workflow, algorithms, and business rules. Session beans are analogous to interactive sessions. Just as an interac tive session isn’t shared among users, a session bean is not shared among clients. Like an interactive session, a session bean isn’t persistent (that is, its data isn’t saved to a database). Session beans are removed when the EJB container is shut down or crashes. You can think of a session bean object as an extension of the client on the server side. It works for its client, sparing the client from complexity by executing business tasks inside the server. Session beans typically contain business process lo gic and workflow, such as sending an email, looking up a stock price from a database, and implementing compression and encryption algorithms. There are 3 types of Session beans : Stateless Stateful Singleton I. Stateless Session Beans: A stateless session bean, by comparison, does not maintain any conversational state. Stateless session beans are pooled by their container to handle multiple requests from multiple clients. munotes.in
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Introduction to Enterprise Javabeans 203 II. Stateful Session Beans : A stateful session bean acts on behalf of a single client and maintains client -specific session information(called conversational state) across multiple method calls and transactions. It exists for the duration of a single client/server session. III. Singleton Session Beans: Provide shared data to client and co mponents within an access application and are instantiated only once per application. 16.4.2 Entity Beans: If you’ve worked with databases, you’re familiar with persistent data. The data in a database is persistent; that is, it exists even after the databa se server is shut down. Entity beans are persistent objects. They typically represent business entities, such as customers, products, accounts, and orders. Typically, each entity bean has an underlying table in a relational database, and each instance of the bean corresponds to a row in that table. The state of an entity bean is persistent, transactional, and shared among different clients. It hides complexity behind the bean and container common services. Because the clients might want to change the same data, it’s important that entity beans work within transactions. Entity beans typically contain data -related logic, such as inserting, updating, and removing a customer record in the database. Two types of entity beans are relevant to persistence: • conta iner-managed persistence (CMP) • bean -managed persistence (BMP). In a CMP entity bean, the EJB container manages the bean’s persistence according to the data -object mapping in the deployment descriptor. Any change in the entity bean’s state will be autom atically saved to the database by the container. No code is required in the bean to reflect these changes or to manage the database connection. On the other hand, a BMP entity bean has to manage both the database connections and all the changes to the bean ’s state.(Entity bean that manage their own persistence are called BMP entity bean.) 16.4.3 Message Driven Beans: Message -driven beans are enterprise beans that receive and process JMS messages. Unlike session or entity heans, message -driven be ans have no interfaces. They can be accessed only through messaging and they do not maintain any conversational state. munotes.in
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Enterprise Java 204 Message -driven beans allow asynchronous communication between the queue and the listener, and provide separation between message processing and busi ness logic. Message driven beans are: Do not have home and component interface. Do not have business methods but define message listener method which the EJB container invokes to deliver messages. Do not hold any state between calls of the message listener method. Are relatively short -lived. Can be Transaction aware. Do not represent directly shared data in the database, but they can access and update this data. In synchronous communication, the client blocks until the server -side object completes processin g. In asynchronous communication, the client sends its message and does not need to wait for the receiver to receive or process the message. Session and entity beans process messages synchronously. Message -driven beans, on the other hand, are stateless com ponents that are asynchronously invoked by the container as a result of the arrival of a Java Message Service (JMS) message. A message -driven bean receives a message from a JMS destination, such as a queue or topic, and performs business logic based on the message contents, such as logic to receive and process a client notification. An example of a message -driven bean is when a shopper makes an online purchase order; an order bean could notify a credit verification bean. A credit verification bean could che ck the shopper’s credit card in the background and send a notification message for approval. Because this notification is asynchronous, the shopper doesn’t have to wait for the background processing to complete. 16.5 ACCESSING ENTERPRISE BEANS Enterprise b eans are accessed by the client in two ways either through a no-interface view or through a business interface. • No-interface view : A no -interface view of an enterprise bean exposes the public methods of the enterprise bean implementation class to clients . Clients using the no -interface view of an enterprise bean may invoke any public methods in the enterprise bean implementation class or any superclasses of the implementation class. munotes.in
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Introduction to Enterprise Javabeans 205 • Business interface : A business interface is a standard Java programmi ng language interface that contains the business methods of the enterprise bean. To use a session bean client will have to required either bean's business's interface methods or enterprise bean's public methods which has a no - interface view. Session beans can have more than one business interface. Session beans should, but are not required to, implement their business interface or interfaces. 16.6 HOW TO USE ENTERPRISE BEANS IN CLIENTS The client of an enterprise bean obtains a reference to an instance of an enterprise bean through either dependency injection, using Java programming language annotations, or JNDI lookup, using the Java Naming and Directory Interface syntax to find the enterprise bean instance. Dependency injection is the simplest way of obta ining an enterprise bean reference. Clients that run within a Java EE server -managed environment, Java Server Faces web applications, JAX -RS web services, other enterprise beans, or Java EE application clients, support dependency injection using the javax. ejb.EJB annotation. Applications that run outside a Java EE server -managed environment, such as Java SE applications, explicit lookup. JNDI supports a must perform an global syntax for identifying Java EE components to simplify this explicit lookup. 16.6.1 Remote or Local Access : 1. Local Clients : A local client has these characteristics . • It must run in the same application as the enterprise bean it accesses. • It can be a web component or another enterprise bean. • To the local client, the location of th e enterprise bean it accesses is not transparent. Accessing Local Enterprise Beans Using the No -Interface View : Client access to an enterprise bean that exposes a local, no -interface view is accomplished through either dependency injection or JNDI lookup. To obtain a reference to the no -interface view of an enterprise bean through dependency injection, use the javax.ejb.EJB annotation and specify the enterprise bean's implementation class munotes.in
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Enterprise Java 206 @EJB ExampleBean exampleBean; To obtain a reference to the no -interfa ce view of an enterprise bean through JNDI lookup, use the javax.naming.InitialContext interface's lookup method: ExampleBean exampleBean=(ExampleBean) InitialContext.lookup("java:module/ExampleBean"); Clients do not use the new operator to obtain a new i nstance of an enterprise bean that uses a no -interface view. 16.6.2 Remote Clients : A remote client of an enterprise bean has the following characteristics. It can run on a different machine and a different JVM from the enterprise bean it accesses. (It is not required to run on a different JVM.) It can be a web component, an application client, or another enterprise bean. To a remote client, the location of the enterprise bean is transparent. The enterprise bean must implement a business interface. That is, remote clients may not access an enterprise bean through a no -interface view. Accessing Remote Enterprise Beans Using the business Interface View : Client access to an enterprise bean that implements a remote business interface is accomplished through eit her dependency injection or JNDI lookup. To obtain a reference to the remote business interface of an enterprise bean through dependency injection, use the javax.ejb.EJB annotation and specify the enterprise bean's remote business interface name: @EJB Exam ple: To obtain a reference to a remote business interface of an enterprise bean through JNDI lookup, use the javax.naming.InitialContext interface's lookup method: ExampleRemote example=(ExampleRemote) InitialContext.lookup("java:global/myApp/ExampleRemote "); munotes.in
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Introduction to Enterprise Javabeans 207 16.6.3 Characteristics of Local clients : • They must run in the same application. • Clients can be a web component or other enterprise bean. • To the local client the location of the enterprise bean it accesses is not transparent.
16.6.4 Characterist ics of Remo te clients : • An enterprise bean which will access the client, called remote client if it run on an other machine or JVM however, running on different JVM is not necessary. • Clients can be a web component, an application client, or other enterp rise bean. • To the Remote client the location of the enterprise bean it accesses is transparent • Remote clients which will use an enterprise bean that, enterprise bean will must have to implement the business interface.
Enterprise Java 208 16.7 SUMMARY EJB stands for Enterprise Java Beans . EJB is an essential part of a J2EE platform. J2EE platform has component based architecture to provide multi -tiered, distributed and highly transactional features to enterprise level a pplications. EJB provides an architecture to develop and deploy component based enterprise applications considering robustness, high scalability, and high performance. An EJB application can be deployed on any of the application server compliant with the J 2EE 1.3 standard specification 16.8 REFERENCES 1. Java EE for beginners by -Sharanam Shah 2. Advanced Java Programming by -Uttan Kumar Roy 3. Java EE 8 by -Elder Moreas 4. www.javatutorial.com 16.9 UNIT END QUESTIONS 1. Explain EJB with advantages and disadvantages? 2. Explain different types of EJB? 3. How to use Enterprise Beans in clients? 4. Explain characteristics of local clients? *****
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209 17 WORKING WITH SESSION BEANS AND MESSAGE DRIVEN BEAN Unit Structure 17.0 Objectives 17.1 Introduction 17.1.1 What is Session Beans? 17.1.2 When to use Session Bean? 17.2 Types of Session Beans 17.3 Remote and local Interface 17.4 Accessing Interfaces 17.5 Accessing Local Enterprise Beans That Implement Business Interfaces 17.6 When to Use Message -Driven Beans 17.7 The Lifecycle of a Message -Driven Bean 17.8 Message Driven Bean Example 17.9 Summary 17.10 References 17.11 Uni t End Questions 17.0 OBJECTIVES After going through this chapt er, you will be able to : • Understand use, advantage, disadvantage of Session Beans • When to use session beans. • Type of Session Beans • How to access and beans in different interfaces • Under stand what is message Driven Beans • Life Cycle of Message Driven Beans • Use of Message Driven Beans 17.1 INTRODUCTION 17.1.1 What is Session Bean? : A session bean is an EJB 3.0 or EJB 2.1 enterprise bean component created by a client for the duration of a single client/server session. The session bean performs work for its client, shielding it from complexity by executing business tasks inside the server. munotes.in
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Enterprise Java 210 A session bean is not persistent. (That is, its data is not saved to a database.) A session bean encapsulates business logic that can be invoked programmatically by a client over local, remote, or web service client views. 17.1.2 When to Use Session Beans : Stateful session beans are appropriate if any of the following conditions are true. • The bean’s s tate represents the interaction between the bean and a specific client. • The bean needs to hold information about the client across method invocations. • The bean mediates between the client and the other components of the application, presenting a simpli fied view to the client. • Behind the scenes, the bean manages the work flow of several enterprise beans. To improve performance, you might choose a stateless session bean if it has any of these traits. • The bean’s state has no data for a specific client. • In a single method invocation, the bean performs a generic task for all clients. For example, you might use a stateless session bean to send an email that confirms an online order. • The bean implements a web service. Singleton session beans are appropr iate in the following circumstances. • State needs to be shared across the application. • A single enterprise bean needs to be accessed by multiple threads concurrently. • The application needs an enterprise bean to perform tasks upon application startup a nd shutdown. • The bean implements a web service. 17.2 TYPES OF SESSION BEANS Session beans are of three types: stateful, stateless, and singleton. Stateful Session Beans : The state of an object consists of the values of its instance variables. In a statef ul session bean, the instance variables represent the state of a unique munotes.in
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Working with Session Beans and Message Driven Bean 211 client/bean session. Because the client interacts (“talks”) with its bean, this state is often called the conversational state . As its name suggests, a session bean is similar to an in teractive session. A session bean is not shared; it can have only one client, in the same way that an interactive session can have only one user. When the client terminates, its session bean appears to terminate and is no longer associated with the client. The state is retained for the duration of the client/bean session. If the client removes the bean, the session ends and the state disappears. This transient nature of the state is not a problem, however, because when the conversation between the client an d the bean ends, there is no need to retain the state. Stateless Session Beans : A stateless session bean does not maintain a conversational state with the client. When a client invokes the methods of a stateless bean, the bean’s instance variables may cont ain a state specific to that client but only for the duration of the invocation. When the method is finished, the client - specific state should not be retained. Clients may, however, change the state of instance variables in pooled stateless beans, and this state is held over to the next invocation of the pooled stateless bean. Except during method invocation, all instances of a stateless bean are equivalent, allowing the EJB container to assign an instance to any client. That is, the state of a stateless se ssion bean should apply across all clients. Because they can support multiple clients, stateless session beans can offer better scalability for applications that require large numbers of clients. Typically, an application requires fewer stateless session b eans than stateful session beans to support the same number of clients. A stateless session bean can implement a web service, but a stateful session bean cannot. Singleton Session Beans : A singleton session bean is instantiated once per application and exi sts for the lifecycle of the application. Singleton session beans are designed for circumstances in which a single enterprise bean instance is shared across and concurrently accessed by clients. Singleton session beans offer similar functionality to statel ess session beans but differ from them in that there is only one singleton session bean per application, as opposed to a pool of stateless session beans, any of which may respond to a client request. Like stateless session beans, singleton session beans ca n implement web service endpoints. Singleton session beans maintain their state between client invocations but are not required to maintain their state across server crashes or shutdowns. munotes.in
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Enterprise Java 212 Applications that use a singleton session bean may specify that the singleton should be instantiated upon application startup, which allows the singleton to perform initialization tasks for the application. The singleton may perform cleanup tasks on application shutdown as well, because the singleton will operate throughou t the lifecycle of the application. 17.3 REMOTE AND LOCAL INTERFACES 1. Local interface : The local interface is used for Local client. Local interface are the type of interface that are used for making local connections to EJB. @Local annotation is used fo r declaring interface as Local. Javax.ejb.Local package is used for creating Local interface. Syntax: @Local public interface InterfaceName { ... } Example: Package ejb; import javax.ejb.Local; @Local Public interface SessionLocal { } 2. Remote interface : The Remote interface is used for Remote client. Remote interface are the interface that has the methods that relate to a particular bean instance. @Remote annotation is used for declaring interface as Remote. Javax.ejb.Remote package is used for creating Remote interface. Syntax: @Remote public interface InterfaceName { ... } Example: Package ejb; import javax.ejb.Remote; @Remote Public interface SessionRemote munotes.in
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Working with Session Beans and Message Driven Bean 213 { String getMessage(); String getAddress(); } 17.4 ACCESSING INTERFACES Accessing Loc al Enterprise Beans Using the No -Interface View : Client access to an enterprise bean that exposes a local, no -interface view is accomplished through either dependency injection or JNDI lookup. • To obtain a reference to the no -interface view of an enterpri se bean through dependency injection, use the javax.ejb.EJB annotation and specify the enterprise bean’s implementation class: • @EJB ExampleBean exampleBean; • To obtain a reference to the no -interface view of an enterprise bean through JNDI lookup, use t he javax.naming.InitialContext interface’s lookup method: • ExampleBean exampleBean = (ExampleBean) InitialContext.lookup("java:module/ExampleBean"); Clients do not use the new operator to obtain a new instance of an enterprise bean that uses a no -interface view. 17.5 ACCESSING LOCAL ENTERPRISE BEANS THAT IMPLEMENT BUSINESS INTERFACES Client access to enterprise beans that implement local business interfaces is accomplished through either dependency injection or JNDI lookup. • To obtain a reference to th e local business interface of an enterprise bean through dependency injection, use the javax.ejb.EJB annotation and specify the enterprise bean’s local business interface name: • @EJB Example example; • To obtain a reference to a local business interface o f an enterprise bean through JNDI lookup, use the javax.naming.InitialContext interface’s lookup method: • ExampleLocal example = (ExampleLocal) InitialContext.lookup("java:module/ExampleLocal"); munotes.in
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Enterprise Java 214 17.6 WHEN TO USE MESSAGE -DRIVEN BEANS A message dr iven bean (MDB) is a bean that contains business logic. But, it is invoked by passing the message. So, it is like JMS Receiver. MDB asynchronously receives the message and processes it. A message driven bean receives message from queue or topic, so you mus t have the knowledge of JMS API. A message -driven bean is an enterprise bean that allows Java EE applications to process messages asynchronously. This type of bean normally acts as a JMS message listener, which is similar to an event listener but receives JMS messages instead of events. The messages can be sent by any Java EE component (an application client, another enterprise bean, or a web component) or by a JMS application or system that does not use Java EE technology. Message -driven beans can process JMS messages or other kinds of messages.
Session beans allow you to send JMS messages and to receive them synchronously but not asynchronously. To avoid tying up server resources, do not to use blocking synchronous receives in a server -side component; in general, JMS messages should not be sent or received synchronously. To receive messages asynchronously, use a message - driven bean. 17.7 THE LIFECYCLE OF A MESSAGE -DRIVEN BEAN Figure illustrates the stages in the lifecycle of a message -driven bean. Figure illustrates Lifecycle of a Message -Driven Bean : munotes.in
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Working with Session Beans and Message Driven Bean 215 The EJB container usually creates a pool of message -driven bean instances. For each instance, the EJB container performs these tasks. 1. If the message -driven bean uses dependency injection, the container injects these references before instantiating the instance. 2. The container calls the method annotated @PostConstruct, if any. Like a stateless session bean, a message -driven bean is never passivated and has only two states: nonexistent and ready to receiv e messages. At the end of the lifecycle, the container calls the method annotated @PreDestroy, if any. The bean’s instance is then ready for garbage collection 17.8 MESSAGE DRIVEN BEAN EXAMPLE To create the message driven bean, you need to declare @Message Driven annotation and implement MessageListener interface. In eclipse ide, create EJB Project then create a class as given below: File: MyListener.java 1. package com.javatpoint; 2. import javax.ejb.MessageDriven; 3. import javax.jms.*; 4. 5. @Mes sageDriven(mappedName="myTopic") 6. public class MyListener implements MessageListener{ 7. @Override 8. public void onMessage(Message msg) { 9. TextMessage m=(TextMessage)msg; 10. try{ 11. System.out.println("mes sage received: "+m.getText()); 12. }catch(Exception e){System.out.println(e);} 13. } 14. } 17.9 SUMMARY A message -driven bean is an enterprise bean that allows Java EE applications to process messages asynchronously. This type of bean normally acts as a JMS message listener, which is similar to an event listener but receives JMS messages instead of events. The messages can be sent by any Java EE component (an application client, another enterprise munotes.in
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Enterprise Java 216 bean, or a web component) or by a JMS ap plication or system that does not use Java EE technology. Message -driven beans can process JMS messages or other kinds of messages. The most visible difference between message -driven beans and session beans is that clients do not access message -driven bean s through interfaces. Unlike a session bean, a message -driven bean has only a bean class. A session bean encapsulates business logic that can be invoked programmatically by a client over local, remote, or web service client views. To access an application that is deployed on the server, the client invokes the session bean’s methods . 17.10 REFERENCES 1. Java EE for beginners by -Sharanam Shah 2. Advanced Java Programming by -Uttan Kumar Roy 3. Java EE 8 by -Elder Moreas 4. www.javatutorial.com 17.11 UNIT END QUESTIONS 1. What is session beans? Explain use of session beans. 2. What are the types of session beans? 3. Explain local and remote interfaces 4. What is Message Driven Beans with its uses? 5. Explain Lifecycle of Message Driven Beans? 6. Write a program to show implementation of Message Driven Beans ? ***** munotes.in
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217 18 INTERCEPTORS Unit Structure 18.0 Objectives 18.1 Introduction 18.2 Interceptor Metadata Annotations 18.3 Interceptor Classes 18.4 Interceptor Lifecycle 18.5 The Interceptor Application 18.6 Running the interceptor Example 18.7 Services 18.7.1Na ming Service 18.7.2 Directory Service 18.8 Characteristics of Directory Services 18.9 Architecture 18.10 Different Packages 18.11 Resources and JNDI Naming 18.12 Summary 18.13 References 18.14 Unit End Questions 18.0 OBJECTIVES After going through this chapter, you will be able to : • Understand what is interceptors • LifeCycle of interceptors • Different annotations of interceptors • Understand what is naming directory • Different packages of directory • Its Architecture 18.1 INTRODUCTION Intercept ors are used in conjunction with Java EE managed classes to allow developers to invoke interceptor methods on an associated target class , in conjunction with method invocations or lifecycle events. Common uses of interceptors are logging, auditing, and pro filing. An interceptor can be defined within a target class as an interceptor method , or in an associated class called an interceptor class . Interceptor classes munotes.in
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Enterprise Java 218 contain methods that are invoked in conjunction with the methods or lifecycle events of the tar get class. Interceptor classes and methods are defined using metadata annotations, or in the deployment descriptor of the application containing the interceptors and target classes. 18.2 INTERCEPTOR METADATA ANNOTATIONS Interceptor Metadata Annotation Description javax.interceptor.AroundInvoke Designates the method as an interceptor method. javax.interceptor.AroundTimeout Designates the method as a timeout interceptor, for interposing on timeout methods for enterprise bean timers. javax.annotation.PostConstruct Designates the method as an interceptor method for post-construct lifecycle events. javax.annotation.PreDestroy Designates the method as an interceptor method for pre-destroy lifecycle events. 18.3 INTERCEPTOR CLASSES Interceptor classes may be designated with the optional javax.interceptor.Interceptor annotation, but interceptor classes aren’t required to be so annotated. An interceptor class must have a public, no - argument constructor. The target class can have any number of interceptor classes associated with it. The order in which the interceptor classes are invoked is determined by the order in which the interceptor classes are defined in the javax.interceptor.Interceptors annotation. However, this order can be overridden in the deployment de scriptor. Interceptor classes may be targets of dependency injection. Dependency injection occurs when the interceptor class instance is created, using the naming context of the associated target class, and before any @PostConstruct callbacks are invoked. 18.4 INTERCEPTOR LIFECYCLE Interceptor classes have the same lifecycle as their associated target class. When a target class instance is created, an interceptor class instance is also created for each declared interceptor class in the target class. That is , if the target class declares multiple interceptor classes, an instance of each class is created when the target class instance is created. The target class instance and all interceptor class instances are fully instantiated before any @PostConstruct call backs are invoked, and any @PreDestroy callbacks munotes.in
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Interceptors 219 are invoked before the target class and interceptor class instances are destroyed. 18.5 THE INTERCEPTOR APPLICATION The interceptor example demonstrates how to use an interceptor class, containing an @Around Invoke interceptor method, with a stateless session bean. The HelloBean stateless session bean is a simple enterprise bean with two business methods, getName and setName, to retrieve and modify a string. The setName business method has an @Interceptors ann otation that specifies an interceptor class, HelloInterceptor, for that method. @Interceptors(HelloInterceptor.class) public void setName(String name) { this.name = name; } The HelloInterceptor class defines an @AroundInvoke interceptor method, modifyG reeting, that converts the string passed to HelloBean.setName to lowercase. @AroundInvoke public Object modifyGreeting(InvocationContext ctx) throws Exception { Object[] parameters = ctx.getParameters(); String param = (String) parameters[0]; param = param.toLowerCase(); parameters[0] = param; ctx.setParameters(parameters); try { return ctx.proceed(); } catch (Exception e) { logger.warning("Error calling ctx.proceed in modifyGreeting()"); return null; } } The parameters to HelloBean.setName are retrieved and stored in an Object array by calling the InvocationContext.getParameters method. Because setName has only one parameter, it is the first and only element in the array. The string is set to lowercase and stored in the parameters array, then passed to InvocationContext.setParameters. To return control to the session bean, InvocationContext.proceed is called. munotes.in
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Enterprise Java 220 The user interface of interceptor is a JavaServer Faces web application that consists of two Fa celets views: index.xhtml, which contains a form for entering the name, and response.xhtml, which displays the final name. 18.6 RUNNING THE INTERCEPTOR EXAMPLE You can use either NetBeans IDE or Ant to build, package, deploy, and run the interceptor exampl e. To Run the interceptor Example Using NetBeans IDE : 1. From the File menu, choose Open Project. 2. In the Open Project dialog, navigate to tut -install/examples/ejb/. 3. Select the interceptor folder and click Open Project. 4. In the Projects tab, right -click the interceptor project and select Run. This will compile, deploy, and run the interceptor example, opening a web browser page to http://localhost:8080/interceptor/. 5. Type a name into the form and select Submit. The name will be converted to lowerca se by the method interceptor defined in the HelloInterceptor class. To Run the interceptor Example Using Ant : 1. Go to the following directory: tut-install/examples/ejb/interceptor/ 2. To compile the source files and package the application, use the follow ing command: ant This command calls the default target, which builds and packages the application into a WAR file, interceptor.war, located in the dist directory. 3. To deploy and run the application using Ant, use the following command: ant run This comma nd deploys and runs the interceptor example, opening a web browser page to http://localhost:8080/interceptor/. 4. Type a name into the form and select Submit : The name will be converted to lowercase by the method interceptor defined in the Hello Intercepto r class. munotes.in
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Interceptors 221 18.7 SERVICES The Java Naming and Directory Interface™ (JNDI) is an application programming interface (API) that provides naming and directory functionality to applications written using the Java™ programming language. It is defined to be indepen dent of any specific directory service implementation. Thus a variety of directories -new, emerging, and already deployed can be accessed in a common way. 18.7.1 Naming Service: The Java Naming and Directory Interface (JNDI) is an application programming i nterface (API) for accessing different kinds of naming and directory services. JNDI is not specific to a particular naming or directory service, it can be used to access many different kinds of systems including file systems; distributed objects systems li ke CORBA, Java RMI, and EJB; and directory services like LDAP, Novell NetWare, and NIS+. JNDI is similar to JDBC in that they are both Object -Oriented Java APIs that provide a common abstraction for accessing services from different vendors. While JDBC can be used to access a variety of relational databases, JNDI can be used to access a variety of of naming and directory services. Using one API to access many different brands of a service is possible because both JDBC and JNDI subscribe to the same architec tural tenet: Define a common abstraction that most vendors can implement. The common abstraction is the API. It provides an objectified view of a service while hiding the details specific to any brand of service. The implementation is provided by the vendo r, it plugs into the API and implements code specific to accessing that vendor's product. JNDI provides two APIs and one SPI. JNDI has a naming API that allows Java applications to access naming systems like CORBA's Naming services and a directory API that extends the naming service to provide access to directory services like LDAP. JNDI also has a SPI (Service - Provider Interface) which is a programming model that vendors use to write JNDI plug -ins or implementations for their specific product. Each vendor' s plug -in is called a service -provider. A service -provider implements the JNDI APIs so that a Java application can access that vendor's product. For the most part, JNDI hides the implementation details of the a service -provider so that Java developer that uses JNDI can use the same objects and method regardless of the brand of naming or directory service accessed. This is the real power behind APIs like JDBC and JNDI: They provide one programming model for accessing many different products; there is no need to learn a different programming model every time a different product is used. 18.7.2 Directory Service : Directory services are an essential part of today’s network -centric computing infrastructure. Directory -enabled applications now power almost all the mission critical processes of an enterprise, including munotes.in
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Enterprise Java 222 resource planning, value chain management, security and firewalls, and resource provisioning. Directory services also provide the foundation for deployment of e -business and extranet applications. So w hat exactly is a Directory Service? A directory service is the collection of software and processes that store information about your enterprise, subscribers, or both. An example of a directory service is the Domain Name System (DNS), which is provided by DNS servers. A DNS server stores the mappings of computer host names and other forms of domain name to IP addresses. A DNS client sends questions to a DNS server about these mappings (e.g. what is the IP address of test.example.com?). Thus, all of the comp uting resources (hosts) become clients of the DNS server. The mapping of host names enables users of the computing resources to locate computers on a network, using host names rather than complex numerical IP addresses. Whereas the DNS server stores only t wo types of information: names and IP addresses, an LDAP directory service can store information on many other kinds of real -world and conceptual objects. Sun Java System Directory Server stores all of these types of information in a single, network -access ible repository. You may for example want to store physical device information, employee information (name, E -mail address), contract or account information (name, delivery dates, contract numbers, etc.), authentication information, manufactured production information. It is worth noting that although a directory service can be considered an extension of a 18.8 CHARACTERISTICS OF DIRECTORY SERVICES • Hierarchical naming model : A hierarchical naming model uses the concept of containment to reduce ambiguity between names and simplify administration. The name for most objects in the directory is relative to the name of some other object which conceptually contains it. For example, the name of an object representing an employee of a particular company contains the name of the object representing the company, and the name of the company might contain the name of the objects representing the country where the company operates, e.g. cn=John Smith, o=Example Corporation, c=US. Together the names of all objects in th e directory service form a tree, and each Directory Server holds a branch of that tree, which in the Sun Java System Directory Server documentation is also referred to as a suffix. • Extended search capability : Directory services provide robust search capa bilities, allowing searches on individual attributes of entries. • Distributed information model : A directory service enables directory data to be distributed across multiple servers within a network. munotes.in
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Interceptors 223 • Shared network access : While databases are defined in terms of APIs, directories are defined in terms of protocols. Directory access implies network access by definition. Directories are designed specifically for shared access among applications. This is achieved through the object -oriented schema model. By contrast, most databases are designed for use only by particular applications and do not encourage data sharing. • Replicated data : Directories support replication (copies of director y data on more than one server) which make information systems more acces sible and more resistant to failure. • Datastore optimized for reads : The storage mechanism in a directory service is generally designed to support a high ratio of reads to writes. • Extensible schema : The schema describes the type of data stored in the di rectory. Directory services generally support the extension of schema, meaning that new data types can be added to the directory. 18.9 ARCHITECTURE The JNDI architecture consists of an API and a service provider interface (SPI). Java applications use the J NDI API to access a variety of naming and directory services. The SPI enables a variety of naming and directory services to be plugged in transparently, thereby allowing the Java application using the JNDI API to access their services.
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Enterprise Java 224 Packaging : JNDI is included in the Java SE Platform. To use the JNDI, you must have the JNDI classes and one or more service providers. The JDK includes service providers for the following naming/directory services: • Lightweight Directory Access Protocol (LDAP) • Common Object Request Broker Architecture (CORBA) Common Object Services (COS) name service • Java Remote Method Invocation (RMI) Registry • Domain Name Service (DNS) Other service providers can be downloaded from the JNDI page or obtained from other vendors. 18.10 DIFFERENT PACKAGES The JNDI is divided into five packages: • javax.naming • javax.naming.directory • javax.naming.ldap • javax.naming.event • javax.naming.spi Naming Package : The javax.naming package contains classes and interfaces for accessing naming services. Context : The javax.naming package defines a Context interface, which is the core interface for looking up, binding/unbinding, renaming objects and creating and destroying subcontexts. Lookup : The most commonly used operation is lookup(). You sup ply lookup() the name of the object you want to look up, and it returns the object bound to that name. Bindings : listBindings() returns an enumeration of name -to-object bindings. A binding is a tuple containing the name of the bound object, the name of the object's class, and the object itself. munotes.in
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Interceptors 225 List: list() is similar to listBindings(), except that it returns an enumeration of names containing an object's name and the name of the object's class. list() is useful for applications such as browsers that want to discover information about the objects bound within a context but that don't need all of the actual objects. Although listBindings() provides all of the same information, it is potentially a much more expensive operation. Name : Name is an interface that represents a generic name —an ordered sequence of zero or more components. The Naming Systems use this interface to define the names that follow its conventions as described in the Naming and Directory Concepts lesson. References : Objects are stored in nam ing and directory services in different ways. A reference might be a very compact representation of an object. The JNDI defines the Reference class to represent reference. A reference contains information on how to construct a copy of the object. The JNDI will attempt to turn references looked up from the directory into the Java objects that they represent so that JNDI clients have the illusion that what is stored in the directory are Java objects. 18.11 RESOURCES AND JNDI NAMING In a distributed applicatio n, components need to access other components and resources, such as databases. For example, a servlet might invoke remote methods on an enterprise bean that retrieves information from a database. In the Java EE platform, the Java Naming and Directory Interface (JNDI) naming service enables components to locate other components and resources. A resource is a program object that provides connections to systems, such as database servers and messaging systems. (A Java Database Connectivity resource is sometime s referred to as a data source.) Each resource object is identified by a unique, people -friendly name, called the JNDI name. For example, the JNDI name of the JDBC resource for the Java DB database that is shipped with the GlassFish Server is jdbc/__defaul t. An administrator creates resources in a JNDI namespace. In the GlassFish Server, you can use either the Administration Console or the asadmin command to create resources. Applications then use annotations to inject the resources. If an application uses resource injection, the GlassFish Server invokes the JNDI API, and the application is not required to do so. However, it is also possible for an application to locate resources by making direct calls to the JNDI API. munotes.in
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Enterprise Java 226 A resource object and its JNDI name are bound together by the naming and directory service. To create a new resource, a new name/object binding is entered into the JNDI namespace. You inject resources by using the @Resource annotation in an application. You can use a deployment descriptor to ov erride the resource mapping that you specify in an annotation. Using a deployment descriptor allows you to change an application by repackaging it rather than by both recompiling the source files and repackaging. However, for most applications, a deploymen t descriptor is not necessary. Data source resource definition in Javav EE : DataSource resources are used to define a set of properties required to identify and access a database through the JDBC API. These properties include information such as the URL of the database server, the name of the database, and the network protocol to use to communicate with the server. DataSource objects are registered with the Java Naming and Directory Interface (JNDI) naming service so that applications can use the JNDI API t o access a DataSource object to make a connection with a database. Prior to Java EE 7, DataSource resources were created administratively as described in Configuring WebLogic JDBC Resources in Administering JDBC Data Sources for Oracle WebLogic Server. Jav a EE 7 provides the option to programmatically define DataSource resources for a more flexible and portable method of database connectivity. The name element uniquely id entifies a DataSource and is registered with JNDI. The value specified in the name ele ment begins with a namespace scope. Java EE 7 includes the following scopes: • java:comp : Names in this namespace have per -component visibility. • java:module : Names in this namespace are shared by all components in a module, for example, the EJB component s defined in an a ejb - jar.xml file. • java:app : Names in this namespace are shared by all components and modules in an application, for example, the application -client, web, and EJB components in an .ear file. • java:global : Names in this namespace are sha red by all the applications in the server. 18.12 SUMMARY Interceptors are used in conjunction with Java EE managed classes to allow developers to invoke interceptor methods on an associated target class, in conjunction with method invocations or lifecycle events . Common uses of interceptors are logging, auditing, and profiling. munotes.in
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Interceptors 227 Clients use the naming service to locate objects by name . The Java Naming and Directory Interface (JNDI) is designed by Sun Microsystems Ltd. to simplify access to the directory infr astructure, which advanced network applications are being built on, by providing an unified set of interfaces 18.13 REFERENCES 1. Java EE for beginners by -Sharanam Shah 2. Advanced Java Programming by -Uttan Kumar Roy 3. Java EE 8 by -Elder Moreas 4. www.javatutorial.com 18.14 UNIT END QUESTIONS 1. What is interceptors with different annotations? 2. Explain interceptors lifecycle? 3. Explain the steps for running interceptors application? 4. Explain interceptors with example? 5. What is naming ser vice and directory service ? 6. Explain Characteristics of Directory Service? 7. Explain different packages of java naming directory?
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228 UNIT V 19 PERSISTENCE, OBJECT/RELATIONAL MAPPING AND JPA Unit Structure 19.1 Objectives 19.2 Persistence, Object/Relational Mapping And JPA 19.3 What is Persistence? 19.4 Persistence in Java 19.5 Current Persistence Standards in Java 19.6 Why another Persistence Standards? 19.7 Object/Relational Mapping 19.8 Summary 19.9 Sample Questions 19.10 References 19.1 OBJECTIVES This chapter will introduce Data Persistence it’s means for an application to persist and retrieve information from a non -volati le storage system. Persistence is vital to enterprise applications because of the required access to relational databases. 19.2 PERSISTENCE, OBJECT/RELATIONAL MAPPING AND JPA Data is an important asset to any computer application. All computer applications require that a person or another computer access their data. This data is used in different ways. Data can be: Read -only Read -write Read for update over multiple requests Modified through batch updates Used in bulk data retrieval The attention span of a c omputer is only as long as its cord is connected to a power supply. The precious data is within the confines of electronic munotes.in
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Persistence, Object/Relational Mapping and JPA 229 memory. If the application does not preserve data when it was powered off, the application is of little or rather no practical use. H ence, it is required to make the precious data live longer than the application. This is where Persistence comes in. 19.3 WHAT IS PERSISTENCE? Most business applications require that data must be persistent. Data can be labeled as persistent only when it m anages to survive day to day problems such as system crashes and network failures. Often multiple users request for data simultaneously. Here, there is a definite possibility of data getting corrupt, if mid -request, system failure, occurs. Maintaining the persistence of data in an enterprise wide application is quite a challenging job. In enterprise application architecture, data persistence is implemented as: Having data stored outside an application’s active memory, known as persistent data store , typical ly, a relational database or an object database or a flat file system Having a rollback system , where, in case of system failure, the state of the data is rolled back to its last known valid data state Persistence is one of the fundamental concepts of appl ication development . It allows DATA to outlive the execution of an application that created it. It is one of the most vital pieces of an application without which all the data is simply lost. Majority of applications use persistent data. For example, GUI a pplications need to store user preferences across program invocations, Web applications track user movements and orders over long periods of time. Hence, it is imperative to choose an appropriate persistence data store. Often when choosing the persistence data store the following fundamental qualifiers are considered: 1. The length of time data must be persisted 2. The volume of data Application may consider an HTTP session when the life of a piece of data is limited to the user’s session. However, persis tence over several sessions or several users requires a larger data store. Large amounts of data should not be stored in an HTTP session, instead a database should be considered. The type of database that is chosen also plays an important influence on the architecture and design. 19.4 PERSISTENCE IN JAVA Most of enterprise systems and applications save data into a relational database of some kind. This is why persistence has been a major application development concern for many decades. Persistence in Java munotes.in
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Enterprise Java 230 usually means storing data in a relational database using SQL. In Java, persistence is accomplished by storing data in a Relational Database Management System [RDBMS]. SQL is used to get data in and out of the relational database. Java Database Connectivit y [JDBC]: The Java API IS used to connect to the RDBMS and fire SQL statements. Persistence of Object -Oriented Models : Today most of the development is carried out in an object -oriented manner using languages such as Smalltalk, C++ and Java. Object [Domain ] modelling is a concept always linked with Persistence. In fact, it is often the domain model that is persisted. Object Oriented Programming is based on OBJECTS that represent the business model [the real world]. Objects are easily traversed through relationship graphs using inheritance, associations. When thinking in terms of Java as the programming language of choice, the business logic of an application works with Objects of different class types. However, when dealing with the data store, it’s importa nt to note that the tables of a database are not Objects, which becomes an issue. This is where the concept of Object Persistence comes in. Object Persistence deals with persistence in object -oriented programs such as Java. It means determining how objects and their relationships are persisted in a relational database. Object persistence is about: Mapping object state Determining how an object’s state [data stored in member variables of an object] is stored in database table columns Dealing with the fact th at object state types may not align with relational database types Mapping object relationships Determining how associations between objects are stored as relational database keys or in relational database intersection tables Why Object -Oriented Models? Business logic can be implemented in Java as opposed to stored procedures Design patterns and sophisticated object -oriented concepts such as inheritance and polymorphism can be used Provides code reusability and maintainability In most of the applications, storing and retrieving information usually involves some kind of interaction with a relational database. munotes.in
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Persistence, Object/Relational Mapping and JPA 231 Why Relational Database? : Today, computer applications that involve storing data, involve accessing a relational database. Relational databases are the persistence store for most applications. A relational database is a choice because of the following: It is a proven data persistence technology Provides flexible and robust approach to data management It is the De -facto standard in software development 19.5 CURRENT PERSISTENCE STANDARDS IN JAVA The Java platform was always supported for managing persistence to relational databases. It provides programming interfaces that in turn provide gateway to the relational databases. There already exist the following options that allow the Java developers to store and retrieve persistent data: Serialization JDBC EJB 2 Entity Beans Java Data Objects Serialization : Serialization allows transforming an object graph into a series of bytes, which can then be sent over the network or stored in a file. Serialization seems to be quite simple, but it has a few limitations: 1. Unsuitable for Large Amount of Data: It must store and retrieve the entire object graph at once. This makes it unsuitable for dealing with large amounts of data. 2. Lacks strict data integrity: Changes made to objects cannot be undone, if an error occurs while updating information. This makes it unsuitable for applications that require strict data integrity. 3. No Concurrent Access to Information: Multip le threads or programs cannot read and write the same serialized data concurrently without conflicting with each other. 4. No Querying Capability: It provides no query capabilities. JDBC : JDBC overcomes a lot of limitations that serialization has such as: 1. It can handle large amounts of data munotes.in
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Enterprise Java 232 2. Ensures data integrity 3. Supports concurrent access to information 4. Provides a sophisticated query language in SQL Unfortunately, JDBC does not provide ease of use. JDBC was not designed for storing objects . JDBC allows the Java programs to fully interact with the database. However, this interaction is heavily reliant on SQL. It requires a considerable amount of code spec that deals with taking tabular row and column data and converting it back and forth int o objects. EJB 2 Entity Beans : The Enterprise Edition of the lava platform introduced entity Enterprise JavaBeans [EJBs] EJB 2.x entities are components that represent persistent information in a data store. EJB 2.x entities: Provide an object -oriented vie w of persistent data Use a strict standard, making them portable across vendors Unfortunately, EJB 2.x entities: Are slow Are difficult to code Are not serializable Require a one -to-one mapping to database tables Require expensive application servers to ru n, as they have to reside within a J2EE application server environment Require developers to determine which bean field maps to which table column Do not offer features such as inheritance, polymorphism and complex relations Java Data Objects : Java Data Ob jects [JDO] was initiated to provide another persistence specification effort due to the failures of the EJB persistence model. JDO : Provides an object -oriented query language, which was not well accepted by the relational database users munotes.in
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Persistence, Object/Relational Mapping and JPA 233 Supports non -relational databases. In fact, it was driven by members of the object -oriented database community and is now being adopted by object -oriented database products as the primary API JDO never became an integrated part of the enterprise Java platform. It had many g ood features in it and was adopted by a small community of devoted and loyal users who stuck by it and tried to promote it. Unfortunately, the major commercial vendors did not share the same view of how a persistence framework should be implemented. 19.6 W HY ANOTHER PERSISTENCE STANDARDS? The answer to this question is that, each of the above -mentioned persistence solutions have severe limitations. Object/ Relational Mapping : The object oriented [domain] model use classes, whereas the relational databases u se tables. This creates a gap [The Impedance Mismatch] . Getting the data and associations from objects into relational table structure and vice versa requires a lot of tedious programming due to the difference between the two. This difference is called The Impedance Mismatch . Developers need something simple to convert from one to the other automatically. Bridging the gap between the object model and the relational model is known as Object -Relational Mapping [O -R mapping or ORM].
The Impedance Mismatch : This issue arises as the design of relational data and object -oriented instances share a very different relationship structure within their respective environments. Relational databases are structured in a tabular manner and the object -oriented instances a re structured in a hierarchica l manner. This means that in this object -oriented world, data is represented as OBJECTS [often Called DOMAIN model]. However, the storage medium is based on a RELATIONAL paradigm. Hence, there exists an inevitable mismatch, th e so -called Object/Relational Impedance Mismatch which creates a vacuum between the Object -Oriented Model of a well -designed application [the DOMAIN model] and the relational model in a database schema. This vacuum is surprisingly wide. munotes.in
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How to Map One to the Other? : The most native approach that is usually taken is a simple mapping between each class the database table. This approach requires writing a lot of code spec that maps one to the other. This code spec is often complex, tedious and costly to deve lop.
The Solution to The Impedance Mismatch : This impedance mismatch has led to the development of several different object persistence technologies attempting to bridge the gap between the relational world and the object -oriented world. Hence the soluti on is using an Object Relational Mapping Tool . An Object Relational Mapping Tool provides munotes.in
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Persistence, Object/Relational Mapping and JPA 235 a simple, API for storing and retrieving Java objects directly to and from the relational database. Object/Relational Mapping [ORM] is a technique that allows an application written in an object oriented language to deal with the information [it manipulates] as objects, rather than using database specific concepts such as ROWS, COLUMNS and TABLES which is facilitated by a software called Object/Relational Mapper . An Object/Relational Mapper is a piece of software that is used to transform: An OBJECT view of the data INTO A RELATIONAL view Object/Relational Mapper also offers persistence services [CRUD] such as: 1. CREATE 2. READ 3. UPDATE 4. DELETE O/R mapping is pe rformed by a persistence framework. This framework knows how to: Query the database to retrieve objects Persist those objects back to their representation in the database’s tables and columns All this is known with the help of Mappings. Mappings are define d in metadata , typically annotations. ORM has several benefits. In particular: Eliminates writing SQL to load and persist object state, leaving the developer free to concentrate on the business logic Enables creating an appropriate DOMAIN model, after whic h, the developer only needs to think in terms of OBJECIS, rather than TABLES, ROWS and COLUMNS Reduces dependence on database specific SQL and thus provides Portability across databases Reduces more than 30% of the amount of Java code spec that needs to be written by adopting an ORM munotes.in
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19.7 OBJECT/RELATIONAL MAPPING An ORM provides the following advantages: 1. Better System Architecture: Most of the times all the application functionality and the database access code spec is held together. This brings in so me severe disadvantages. It becomes really difficult to reuse code spec. Hence code repetitions occur at several different places. Changing anything becomes quite difficult, as each and every place that holds the repetitive code spec needs to be located an d changed accordingly. If the application functionality [business logic] and the database access code spec [persistence mechanism] are separated, applying changes become very easy. Changes can be made to one part without influencing the other parts. 2. Red uce Coding Time: Most of the time the database access code spec is simple inserts, updates or deletes. These are SQL statements which sometimes are quite tedious to code. ORM tool helps here, by generating them on the fly and thereby saves a lot of time. 3. Caching and Transactions: Most ORM tools such as Hibernate come with features such as Caching and Transactions. These features, if chosen to hand code are not so easy to implement. And it definitely does not make sense to develop them when they already exist. munotes.in
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Persistence, Object/Relational Mapping and JPA 237 Where Does Java Persistence API Fit In? : Today, there are several good ORM tools available that perform the mapping between objects Relational Database Tables and thereby solve the Impedance Mismatch: 1. Hibernate 2. OpenJPA 3. TopLink 4. EclipseLink These Object -Relational Mapping tools/frameworks allow the developers to focus on the object model instead of dealing with the mismatch between the object -oriented and relational paradigms. Unfortunately, each of these tools has its own set of API s. This ties the application code spec to the proprietary interfaces of a specific vendor [ORM tool]. Since the code spec is tied to a specific vendor [referred to as Vendor Lock -In], switching to another tool is not possible without rewriting all the pers istence code spec. Java Persistence API : The Java Enterprise Edition’s [Java EE 5] Enterprise JavaBeans 3 has introduced a new way of communicating with databases called the lava Persistence API [JPA], a section of EJB 3.0. JPA defines a persistence framew ork which provides a way of automatically mapping normal Java objects to an SQL database. In other words, it helps load, search and save the data model objects. JPA combines the best features from most of the available persistence standards: Is extremely e asy to use, entities can be created as simple as creating serializable classes Supports large data sets Provides data consistency Allows concurrent use of information Provides querying capabilities of JDBC Allows using advanced object -oriented concepts suc h as inheritance Java Persistence API As A Specification : JPA is a specification from Sun, which is released under Java EE 5 specification. munotes.in
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Enterprise Java 238 It is not: An implementation A product Hence, it cannot be used as it is for persistence. It needs an ORM implement ation to work with and persist Java Objects. Technically, JPA is just a set of interfaces [a Specification] and thus requires an implementation. All specifications require vendors or open source projects to implement them. Using JPA therefore requires pick ing up an implementation [ORM tool such as Hibernate, Toplink, OpenJPA or any other ORM that implements JPA]. JPA defines the interface that an implementation has to implement. The whole point of having a standard interface is that users can, in principle, switch between implementations of JPA without changing their code. This way, JPA helps prevent Vendor Lock -In by relying on a strict specification such as JDO and EJB 2.x entities. Currently most of the persistence vendors [ORM tool providers] have releas ed implementations of JPA. Since, the Java Persistence code spec covers several persistence frameworks into a single API, an application written using JPA will work across several implementations [Hibernate Toplink and so on]. This is very useful, especial ly when, development begins using the free ‘open source ORM implementations and later on when the need arises, the open source’ implementation is swapped with a commercial ORM implementation. JPA 1.0 as a part of EJB 3 : After the failure of EIB 2, BIB 3.0 came into existence to make Enterprise JavaBeans easier and more productive to use. EJB 3.0 introduced a new model for persistence called The Java Persistence API 1.0. Developers from the leading vendors of object -relational mapping solutions such as Hiber nate, Toplink and JDO joined the Java group and helped shape the new EJB specification. This resulted into a new specification of EJB 3.0 [Java EE 5] with the following distinct pieces: 1. Existing EJB 2.1 APIs and the traditional contracts from the persp ectives of the container, the bean provider and the client with new features such as Java EE injection, EJB 3.0 interceptor Specifications and lifecycle call -back changes 2. A simplified API for developing new session and message -driven components 3. The Java Persistence API Even though, Java Persistence API is defined as part of the EJB 3.0 specification, it is not needed to have an EJB container or a Java EE application server in order to run applications that use persistence. munotes.in
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Persistence, Object/Relational Mapping and JPA 239 19.8 SUMMARY Data Persist ence is a means for an application to persist and retrieve information from a non -volatile storage system. Persistence is vital to enterprise applications because of the required access to relational databases. 19.9 PRACTICE QUESTIONS: MCQ: Q.1) Which one of the following best illustrates the concept of Object Persistence. a) Determining how an object’s state[data stored in member variable of an object ]is stored in database table columns. b) Provides an object – oriented view of persistent data. c) Design patterns and sophisticated object oriented concepts such as inheritance and polymorphism can be used. d) Provide one to one mapping to database table. Answer: A Q.2) Which of the following is not a correct explanation of JDO. a) JDO is a standard way to ac cess persistent data in databases, using plain old Java objects (POJO) to represent persistent data. b) JDO is an object relational mapping tool. c) Provides object relational query language and support non -relational databases. d) JDO was popular and an integrated part of enterprise java platform. Answer: D Q.3) What is ORM. a) Object Relation Map b) Object Rate Mapping c) Object Relational Mapping d) Object Relational Mapper Answer: C munotes.in
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Enterprise Java 240 Q.4) Which method is used to remove a persistent instance from the datastore. a) Session.remove() b) Session.delete() c) Session.del() d) Session.rm() Answer: B Q.5) Which tool provides a set of persistent annotati ons to define mapping metadata. a) JPA b) JSR c) XML d) JRE Answer: A Q.6) Which of the following simplifies Object Relational Mapping tool. a) Data Creation ,Data Isolation, Data Access b) Data Manipulation, Data Creation, Data Extraction c) Data Crea tion, Data Manipulation, Data Access d) Data Isolation, Data Extraction, Data Manipulation Answer: C Q.7) The problem which arises because of the difference between model of programming language and model of database is classified as. a) modelling mismatch b) referential mismatch c) dependence mismatch d) impedance mismatch Answer: D Q.8) An ORM Framework persist your objects according to the mapping metadata you provide. a) False b) True munotes.in
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Persistence, Object/Relational Mapping and JPA 241 c) May be d) Can’t say Answer: B Q.9) Which technique is used by Hibe rnate to persist collections of embeddable types. a) ElementCollection b) ManyToMany c) OneToMany d) CollectionElement Answer: A Q.10) What is the JPA equivalent of hibernate.cfg.xml file. a) configuration.xml b) persistence.xml c) jpa.configuration.xm l d) jpa.persistence.xml Answer: B Descriptive: 1. Write a note on Java Persistence API. 2. Explain the architecture of JPA 2.0. 3. What is Persistence? 4. What are the various options that allow the Java developers to store and retrieve persistent dat a? 5. What is Object/Relational Mapping? 6. List and explain various advantages provided by Object Relational Mapping. 19.10 REFERENCES Books and References: Sr. No. Title Author/s Publisher Edition Year 1. Java EE 7 For Beginners Sharanam Shah, Vaishali SPD First 2017 munotes.in
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Enterprise Java 242 Shah 2. Java EE 8 Cookbook: Build reliable applications with the most robust and mature technology for enterprise development Elder Moraes Packt First 2018 3. Advanced Java Programming Uttam Kumar Roy Oxford Press NA 2015
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243 20 JAVA PERSISTENT API Unit Structure 20.1 Objectives 20.2 Introduction to Java Persistence API 20.3 Writing JPA Application 20.4 Summary 20.5 Sample Questions 20.6 References 20.1 OBJECTIVES In this chapter we will learn the Java Persistence API ( JPA) specification of Java. Also learn how it is used to persist data between Java object and relational database. JPA acts as a bridge between object -oriented domain models and relational database systems. As JPA is just a specification, it doesn't perfor m any operation by itself. It requires an implementation. So, ORM tools like Hibernate, TopLink and iBatis implements JPA specifications for data persistence. 20.2 INTRODUCTION TO JAVA PERSISTENCE API 20.2.1 Introduction to Java Persistence API : Convention ally when a programmer is dealing with applications, he/she probably imagines that an application has some specific functions [business logic / application logic] and all that it has to do is process and then finally save data in a database. When thinking in terms of Java as the programming language of choice for most programmers, the business logic of an application works with OBJECTS of different CLASS types. However, when dealing with the storage medium, it’s important to note that the tables of a databa se are not OBJECT. This becomes a little difficult to handle. Today, there are several Object/Relational mapping tools that have become popular because they help bridge up the gap between the Objects and the relational database which in turn allows the dev elopers concentrate on the business logic: Hibernate TopLink EclipseLink OpenJPA munotes.in
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Enterprise Java 244 And many others are available, unfortunately, each of these tools has its own set of APIs. This ties the application code spec to the proprietary interfaces of a specific ven dor [ORM tool]. In spite of having so many Object/Relational mapping tools, there is no single persistence standard for the Java platform that can be used in both the Java EE and Java SE environments. This is where Java Persistence API comes in. JPA helps standardize the persistence API for the Java platform. A lot of these Object/ Relational tool vendors [such as TopLink and Hibernate, as well as other leading application server vendors and JDO vendors] have widely accepted the JSR -220 specification and mo st of them have also released their implementation of JPA. 20.2.2 The Java Persistence API : The Java Persistence API is a standard API that allows accessing, persisting and managing data between Java objects / classes and the relational database in Java EE 5 platform. JPA was defined as a part of the EJB 3.0 specification as a replacement to the EJB 2 CMP (Container - Managed Persistence) Entity Beans specification. It is now considered the standard industry approach for Object Relational Mapping in the Jav a Industry. With the help of a standard API, JPA provides standard mechanisms to using Object Relational Mapping tools. Java Persistence consists of three areas: The Java Persistence API Object/ Relational mapping metadata The Query language Object -relatio nal mapping with the Java Persistence API is entirely metadata driven. It can be done by adding annotations to the code spec OR using externally defined XML 0R using annotations as well as externally defined XML. JPA uses Annotations or XML to map Objects to a Relational Database. These Objects are called Entities. Entities are nothing but POJOs that do not extend any class nor implement any interface. JPA also allows querying and retrieving data using its own query language called Java Persistence Query La nguage. It generates all the necessary SQL calls to achieve this and thereby, relieves the developers from manual result -set handling and object conversion.
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Java Persistent API 245 20.2.3 JPA, ORM, Database and the Application :
JPA is made up of a few classes and interfaces . The application communicates with the configured IPA provider [in this case EclipseLink] to access the underlying data. Typically, applications invoke the appropriate methods of the Java Persistence API. These methods are passed the persistence objects a nd instructed to operate upon them. The information about the mapping [metadata] between the instance variables of classes and the columns of the tables in the database is available either in XML and/ or POJOs with the help of Annotations. POJOs are Java c lasses that represent the tables in the database. Data Access Object [DAO] is the design pattern that can be used [if required] to deal with database operations. EclipseLink uses the database [using JDBC API internally] and refers to the metadata to provid e persistence services [and Persistent Objects] to the application. The application talks to EclipseLink via the JPA to perform the SELECT, INSERT, UPDATE and DELETE operations on the database tables. The ORM tool automatically creates the required SQL que ries and fires them using the JDBC APIs. 20.2.4 Architecture of JPA : munotes.in
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Enterprise Java 246 Persistence: The javax.persistence.Persistence class contains static helper methods to obtain EntityManagerFactoryinstances in a vendor -neutral fashion. EntityManagerFactory: The Enti tyManagerFactory is created with the help of a Persistence Unit during the application start up. It serves as a factory for spawning EntityManager objects when required. Typically, it is created once [one EntityManagerFactory object per database] and for l ater use kept alive for later use.The javax.persistence.EntityManagerFactory class is a factory for EntityManagers. EntityManager: The EntityManager object [javax.persistence.EntityManager] is lightweight and inexpensive to create. It provides the main i nterface to perform actual database operations. All the POJOs i. e. persistent objects are saved and retrieved with the help of EntityManager object. Typically, EntityManager objects are created as needed and destroyed when not required. Each EntityManager manages a set of persistent objects and has APIs to insert new Objects and delete existing ones. EntityManagers also act as factories for Query instances and CriteriaQuery instances. Entity: Entites are persistent objects that represent datastore records . Entity Transaction: A Transaction represents a unit of work with the database. Any kind of modifications initiated via the EntityManager object are placed within a transaction. An EntityManager object helps creating an EntityTransaction object. Transact ion Objects are typically used for a short time and are closed by either committing or rejecting. Query: Persistent objects are retrieved using a Query object. Query objects [javax.persistence.Query] allows using SQL or Java Persistence Query Language [JP QL] queries to retrieve the actual data from the database and create objects. Criteria : Criteria API IS a non -string -based API for the dynamic construction of object -based queries [javax.persistence.criteria]. Just like JPQL static and dynamic queries, cr iteria query objects are passed to the EntityManager’screateQuery() method to create Query objects and then executed using the methods of the Query API. A CriteriaQuery object can be thought of as a set of nodes corresponding to the semantic constructs of the query: munotes.in
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Java Persistent API 247 Domain objects, which correspond to the range variables and other identification variables of the JPQL FROM clause WHERE clause predicates, which comprise one or more conditional expression objects SELECT clauses, which comprise one or more sele ct item objects ORDER -BY and GROUP -BY items Subqueries 20.2.5 How JPA works? : An XML is created or annotations are added to POJOS, which inform the JPA provider [such as Eclipselink] about: 1. The classes needed to Store the data 2. How the classes are r elated to the tables and columns in the database This way all the necessary information is provided to the JPA provider. During the runtime, the IPA provider reads the XML and/or annotations and dynamically builds Java classes to manage the translation bet ween the database and the Java objects. An EntityManagerFactory is created from the compiled collection of mapping metadata. The EntityManagerFactory provides the mechanism for managing persistent classes and the EntityManagerinterface. The EntityManager c lass provides the interface between the persistent data store and the application. The EntityManager interface wraps a JDBC connection, which can be user managed or controlled by the JPA provider and is only intended to be used by a single application thre ad, then closed and discarded. All the database interaction is done via a simple, intuitive API that JPA provides. This allows performing queries against the objects represented by the database. This API informs the JPA provider: To save the changes whenev er the objects are changed To store the objects in the database whenever new objects are created Based on all the above discussion, the following is what will be required to build an application that persists data. An ORM tool: To avoid low level JDBC and SQL code To leverage object -oriented programming and object model usage To provide database and schema independence Since it’s free [Most ORMs are free and open source] munotes.in
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Enterprise Java 248 To use high end performance features such as caching and sophisticated database and que ry optimizations JPA: To gain portability across application sewers and persistence providers [ORMs] Since it’s a standard and part of EJB 3 and Java EE Since it provides a usable and functional specification Since it supports both Java EE and Java SE 20.2.6 JPA Specification : Specification is part of Java EE 6 where IPA has been officially separated from distinct API. JPA 2.0 brings in the following enhancements: 1. ORM mapping enhancements such as: (a) Ability to model collections, maps and lists using @ElementCollection annotation (b) Ability to map unidirectional one -to-many relationships as JPA 1.0 only allowed Bidirectional one -to-many relationships 2. EntityManager and the Query APIs now support: (a) Retrieving the first result (b) Accessing the u nderlying vendor -specific entity manager/ query objects (c) Pessimistic locking 3. JPQL has been enhanced with SQL -like CASE, NULLIF, COALESCE and like capabilities 4. Criteria API similar to the one that Hibernate provides 5. Standardization of: (a) Second level caching (b) Hints for Query configuration and for EntityManager configuration (c) Metadata to support DDL generation and Java2DB mapping 6. Support for validation
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Java Persistent API 249 20.3 WRITING JPA APPLICATION JPA Practical using GuestBook Steps: 1. Create W eb Application with dedicated folder for Library
2. Add Simple java class or Persitent Entity class from Database (code below GuestBook.java) 3. Add SQL Connector Jar file to Library 4. Create Persistence Unit using jdbc connection to MySQL database 5. Create the JSP files (codes given below) 6. Run the Application. GuestBook.java ~~~~~~~~~~~~~ package tyit; import javax.persistence.*;
20.4 SUMMARY The Java Pers istence API (JPA) is a specification of Java. It is used to persist data between Java object and relational database. JPA acts as a bridge between object -oriented domain models and relational database systems. As JPA is just a specification, it doesn't per form any operation by itself. It requires an implementation. So, ORM tools like Hibernate, TopLink and iBatis implements JPA specifications for data persistence. 20.5 SAMPLE QUESTIONS MCQ : Q.1 What is the full form of JPQL a) Java Persistence Query Langua ge b) Java Provider Query Language c) Java POJO Query Language d) Java performance query language Ans: a) Java Persistence Query Language Q.2 Which tool automatically creates the required SQL queries a) XML munotes.in
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Enterprise Java 254 b) JPQL c) ORM d) JPA Ans: c) ORM Q.3 Which one is the simple java class that represents a row in a database table. a) Attribute b) Primary key c) foreign key d) Entity Ans: d) Entity Q.4 An object is called persistent if it is stored in the database and can be accessed anytime. This ty pe of entity property is called as a) Persistability b) Persistent Identity c) Transactionality d) Granularity. Ans: a) Persistability Q.5 Which keyword makes possible to filter results after evry join, leading to smaller results after each successive join. a) ON b) delete. c) enter d) remove. Ans: a) ON Q.6 Which annotation is used to link two tables through a relation table? a. @RelationTable b. @JoinTable c. @LinkTable d. @GroupTable munotes.in
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Java Persistent API 255 Ans: b) @JoinTable Q.7 Which annotation is used to create Pk -Fk relat ion b/w two tables? a. @JoinColumn b. @ForeignKey c. @JoinedKey d. @PrimaryKey Ans: a) @JoinColumn Q.8 Which statement(S) is/are incorrect a. Stored procedure may return a value and function must return a value. b. Function has only IN parameter. c. Try and C atch can be used with both stored procedure and function. d. Stored procedure has IN and OUT parameter. Ans: c) Try and Catch can be used with both stored procedure and function. Q.9 Which API is used to define queries for entities and their persistent state by creating query -defining objects a) Criteria API. b) Query API c) Entity API d) Transaction API Ans: a) criteria API Q.10 JPA 2.1 introduced Which method to call databse funtions which are not directly supported by the standard a) delete() b) insert() c) call() d) function() Ans: d) function() Descriptive: munotes.in
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Enterprise Java 256 1. Write a note on Java Persistence API. 2. Explain the architecture of JPA 2.0. 3. Using suitable example explain the various components of JPA. 4. Create simple JPA application to store a nd retrieve Book details. << similar to above example >> 5. Develop a JPA Application to demonstrate use of ORM associations. 20.6 REFERENCES Books and References: Sr. No. Title Author/s Publisher Edition Year 1. Java EE 7 For Beginners Sharanam Shah, Vaishali Shah SPD First 2017 2. Java EE 8 Cookbook: Build reliable applications with the most robust and mature technology for enterprise development Elder Moraes Packt First 2018 3. Advanced Java Programming Uttam Kumar Roy Oxford Press NA 2015
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257 21 HIBERNATE Unit Structure 21.1 Objectives 21.2 Introduction to Hibernate 21.3 Writing Hibernate Application 21.4 Summary 21.5 Sample Questions 21.6 References 21.1 OBJECTIVES In this we will explain What is hibernate and how to install Hibernate & other associated packages to prepare a develop environment for the Hibernate applications. We will work with MySQL database to experiment with Hibernate examples, so make sure you already have setup for MySQL database. 21.2 INTRODUCTION TO HIBERNATE 21.2. 1 What is Hibernate? : Any project that requires database interaction have started looking at ORM tools than considering the traditional approach i.e. JDBC. Hibernate ease the job of programmer in working with traditional database using concrete SQL queries in Java by using java object mapped with data base and allow programmer to interact with database just like other java class or object. The objective of Hibernate is to free the programmer from tedious database interaction and focus on working with java o bjects and features of application instead of worrying about how to work with data from database. Hibernate does this by copying data from database table to java class and saving state of an object to database table. Hibernate is a free, open source, high performance persistent ORM and query tool. Gavin King, founded the Hibernate Project in 2001 at JBoss Inc. [now part of RedHat Inc.] Hibernate provides: Mapping of java classes to Database table. o e.g.: Student.java class → Student table in Oracle Mapping of java data type to SQL data type. munotes.in
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Enterprise Java 258 o e.g.: int → number, String → varchar, java.sql.Date → DateTime, etc. Flexibility in Querying and retrieving data from any database. Freedom to switch to any data base without changing the application logic/presentation logic. 21.2.2 Why Hibernate? : Hibernate is a high -performance Object/Relational persistence and query service, available free under the open source GNU Lesser General Public License (LGPL). Takes ca re of all SQL operations in a java program. Make feel like working with Objects rather than SQL in performing Create, Read, Update and Delete SQL operations. Complete portability across database. Supports IDE like Netbeans by providing plug -in. Cuts down d evelopment time by using Object oriented technology like inheritance, composition and java collection framework. Can have multiple primary key generations through multiple identity column mapping. Hibernate has two cache layers for handling thread safety, non- blocking concurrent data access, connection pooling etc. Allows working with any database like Oracle, MySql, DB2, Sybase, PostgresSQL, Apache Derby, MS SQL Server, MS Access, etc. 21.2.3 Hibernate, Database and The Application
Application program us es persistent objects that represent data from database. Configuration is stored in configuration files like munotes.in
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Hibernate 259 Hibernate.properties and hibernate.cfg.xml to map the objects to corresponding database and hibernate dilect to choose appropriate SQL statement fo r database. A mapping file is used to map instance variables of class to database columns. Hibernate uses JDBC API with JTA to perform database operations like Create, Insert, Update, Delete, Select etc. to automatically fire queries bases on operations pe rformed by application program on java objects. 21.2.4 Components of Hibernate : The main components of Hibernate are: 1. Connection Management: Hibernate solves the problems which arise when a relational database is connected by an application written in o bject oriented programming language style, due to data type differences, manipula tive differences, transactional differences, structural and integrity differences. Connection Management provides efficient connection management and removes the overhead of d atabase interaction from application program. 2. Transaction Management: Transaction in hibernate is managed by JTA and JDBC. It allow to fire more than one SQL query at a time. 3. Object Relation Management: It is used to map java objects to database tabl es. Hibernate stores the persistent objects in session and reads the state of an object to execute appropriate database query. 21.1.5 Architecture of Hibernate : Hibernate is a layered architecture. The main components are Configuration, Session Factory, Session, Transaction, Query and Criteria. Hibernate uses existing Java APIs, like JDBC for database connectivity, Java Transaction API(JTA) for transaction and Java Naming and Directory Interface (JNDI) for easy integration with other enterprise applications .
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Enterprise Java 260 Following is a detailed view of the Hibernate Application Architecture with few important core classes.
Hibernate uses various existing Java APIs, like JDBC, Java Transaction API(JTA), and Java Naming and Directory Interface (JNDI). JDBC provides a rudimentary level of abstraction offunctionality common to relational databases, allowing almost any database with a JDBC driver to supported by Hibernate. JNDI and JTA allow Hibernate to be integrated with J2EE application servers. Configuration: It repre sents properties/configuration of a hibernate application. It the first object created in a hibernate application and created once at the time of application execution. This object reads the configuration file to establish database connection and mapping. This object helps in creating session factory. It represents a configuration or properties file required by the Hibernate. The Configuration object provides two keys components: 1. Database Connection: This is handled through one or more configuration file s supported by Hibernate. These files are hibernate.properties and hibernate.cfg.xml. 2. Class Mapping Setup This component creates the connection between the Java classes and database tables. Session Factory: It is created using configuration object at t he time of application startup to serve as a base for creating light weight sessions conveniently during client’s request. One session factory is created for one database for multiple database multiple session factory objects are created. Session Object: Sessions are single threaded, lightweight objects to communicate with database represented by session class from org.hinernate package. Persistent object are created, saved and retrieved using session object during client interaction. It wraps the Connecti on class from java.sql package and serves as factory for Transaction. The session objects should not be kept open for a long time because they are munotes.in
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Hibernate 261 not usually thread safe and they should be created and destroyed them as needed. Transaction: Transaction is a single threaded object used by application to represent group of SQL queries to form a unit of work called transaction. Transactions in Hibernate are handled by an underlying transaction manager and transaction (from JDBC or JTA). All changes during a s ession are placed within transaction. Transactions are either completed using commit or canceled using rollback. The org.hibernate.Transaction interface provides methods for transaction management. Query: It uses either conventional SQL or Hibernate Query Language (HQL) to communicate with database. It associates the query parameters, restricts the results coming from database and executes queries. Persistent objects are retrieved using query object. Criteria: Criteria objects are used to create and execut e object oriented criteria queries to retrieve objects. 21.2.6 How Hibernate Works? : • All configuration files hibernate.cfg.xml are created to describe about the java classes and there mapping with database tables. • At the time of application startup t hese files are compiled to provide hibernate framework with necessary information. • This dynamically builds java class objects by mapping them to appropriate database table. • A session factory object is created from compiled collections of mapping docu ments. • Session Factory spawns a lightweight session to provide interface between java objects and applications. • Database communication is performed by this session using hibernate API used to map the changes from java object to database table and vice versa. munotes.in
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Enterprise Java 262 21.3 WRITING HIBERNATE APPLICATION In this section we will d evelop a Hibernate application to store Feedback of Website Visitor in MySQL Database. The application to be built is called Guestbook Feedback Entry using Hibernate. This application should be capable of accepting and displaying employee details using database. To achieve this, it should provide a user interface that accepts Guest’s name, message and date. From the application development perspective, the following software will be requ ired on the development machine: 1. Java Development Kit 2. NetBeans IDE 3. MySQL community Server [The database server] 4. JDBC driver for MySQL 5. Hibernate 4.XXX or Higher (ORM Tool) [Available on www.hibernate.org/downloads] create database feedback db; create table GuestBook( vno int PRIMARY KEY AUTO_INCREMENT, vname varchar(50), msg varchar(100), mdate varchar(50) )
Library Files: The Java library [.JAR] i.e. JDBC driver is required. This will be specific to a relational database to be used. In thi s case MySQL is used as the database of choice, hence, the database specific JDBC driver file will be MySQL Connector/J 5.1.10 . The following is the list of jar files required munotes.in
The Applic ation Development Approach : The application will be built using JSP. The data entry form that captures the data will be called index.html and the page that will fetch and display the entries will be called Fetch.jsp . The captured data will be stored in a t able called GuestBook under the feedbackdb MySQL database server . In the Java application, the POJO that will represent the GuestBook database table will be called mypack.GuestBookBean.java . The following steps are required to build this application: 1. Create the database schema munotes.in
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Enterprise Java 264 2. Create the Web application 3. Add the Java libraries to the application 4. Create a POJO to represent the table in the database schema 5. Generate a hibernate configuration file. 6. Annotate the POJO to indicate the mappin g between the JavaBean properties and the columns in the table 7. Create JSPs with code spec: (a) To build a Configuration object (b) To build a SessionFactory object by referencing the Configuration object. (c) To obtain an HiberanteSession object from the SessionFactory (d) To perform the required database operations. GuestBookBean.java package mypack; import javax.persistence.*; @Entity @Table(name="guestbook") public class GuestBookBean implements java.io.Serializable { @Id @GeneratedValue @Column(name="vno") private Integer visitorNo; @Column(name="vname") private String visitorName; @Column(name="msg") private String msg; @Column(name="mdate") private String msgDate; public GuestBookBean() { } public Integer getVisitorNo() { return visitorNo; } public String getVisitorName() { return visitorName; } public String getMsg() { return msg; } public String getMsgDate() { return msgDate; } munotes.in
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Hibernate 265 public void setVisitorNo(Integer vn) { visitorNo = vn ; } public void setVisitorName(String vn) { visitorName = vn; } public void setMsg(String m) { msg = m; } public void setMsgDate(String md) { msgDate=md; } } Source packages new others select category Hibernate Hibernate Configuration Wizard
Hibernate 267 hibSession.save(gb); tx.commit(); out.println("Thank You for your valuable feedback...."); }catch(Exception e){out.println(e);} hibSession.close(); %> Output:
21.4 SUMMARY In this Chapter we studied hibernate and steps to install Hi bernate & other associated packages to prepare a develop environment for the Hibernate applications. We also worked with MySQL database to experiment with Hibernate examples, so make sure you already have setup for MySQL database. 21.5 PRACTICE QUESTIONS MCQ : 1) What is hibernate? a) CRM b) Programming Tool c) ORM d) SQL tool. munotes.in
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Enterprise Java 268 2) Hibernate framework simplifies the development of java application to interact with the database a) True b) False 3) Which of the following is true about SessionFactory object in hibernate? a) SessionFactory o bject configures Hibernate for the application using the supplied configuration file. b) SessionFactory object allows for a Session object to be instantiated. c) The SessionFactory is a thread safe object. d) All options mentioned for this question. 4) Which method is used to update the state of the given instance from the underlying database? a) Session.store() b) Session.keep() c) Session.update() d) Session.load() 5) HOL stands for a) Hibernate Queue Language b) Hibernate Query Language c) Hypertext Query Language d) HighSpeed Query Language 6) Hibernate uses PersisterClassProvider by default. a) True b) Fales 7) _______________ object is used to create SessionFactory object in Hibernate. a) Session b) Configuration c) Transaction d) TransactionFactory munotes.in
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Hibernate 269 8) In hibernate, QBC stands for a) Query By Criteria b) Query By Call c) Query By Code d) Query By Column 9) Which method is easy for Java Programmer to add criterion? a) SQL b) HCQL c) HQL d) AQL 10) Which of the following simplifies an Object Relational Mapping Tool? a) Data creation b) Data manipulation c) Data access d) All options mentioned for this question . 11) _______ is not a core interface of hibernate. a) Criteria b) Session c) SessionManagement d) Configuration 12) Is SessionFactory a ThreadSafe object a) Yes b) No 13) Is Session created per thread in hibernate? a) Yes b) No 14) All POJO must implement non -argument constructor in hibernate. a) True b) False munotes.in
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Enterprise Java 270 15) When several entities point to the target entity, that is achieved by a) @OneToOne b) @OneToMany c) @ManyToOne d) @ManyToMany 16) If entity is not annotated with @Table, what will happen? a) Throws error because no table name is assigned b) No error and class name w ill be mapped with table name. 17) A __________ is used to get a physical connection with a database. a) SessionFactory b) Session c) Transaction d) ConnectionProvider 18) A _________ represents a unit of work with the database and the Java object. a) SessionFactory b) Connectio nProvoder c) Transaction d) Session 19) _________ is a factory of JDBC connections. a) SessionFactory b) ConnectionProvoder c) Transaction d) Session 20) Mapping in hibernate can be given to an ORM tool either in the form of an ______or in the form of the annotations a) XHTML b) JSON c) HTM L d) XML munotes.in
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Hibernate 271 Answers : 1) c 2) a 3) d 4) c 5) b 6) a 7) b 8) a 9) d 10) d 11) c 12) a 13) a 14) a 15) c 16) b 17) b 18) c 19) b 20) d Descriptive: 1. Explain software development approach of Hibernate? 2. Develop a Hibernate application to store and retrieve employee details in MySQL Database. 3. Develop a Hibernate application to store Feedback of Website Visitor in MySQL Database. 4. Develop an application to demonstrate Hibernate One - To -One Mapping Using Annotation.
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Enterprise Java 272 21.6 REFERENCES Books and References: Sr. No. Title Author/s Publisher Edition Year 1. Java EE 7 For Beginners Sharanam Shah, Vaishali Shah SPD First 2017 2. Java EE 8 Cookbook: Build reliable applications with the most robust and mature technology for enterprise development Elder Moraes Packt First 2018 3. Advanced Java Programming Uttam Kumar Roy Oxford Press NA 2015