EJB fundamentals and session beans. Java Enterprise Edition (Java EE) has a powerful facility dedicated to expressing the business logic of an application and for accessing a database using a Java. Beans- like concept. That facility is Enterprise Java. Beans, known as EJBs for short. In this article, we'll begin exploring the world of EJBs, which is a very important capability of the Java EE platform. EJBs provide infrastructure for developing and deploying mission- critical, enterprise applications. We'll first look at some EJB fundamentals, and then focus on one type of EJB: the session bean. In this article, you will learn the following: The benefits of using EJBs. The three kinds of EJBs: session, entity, and message- driven beans. The makeup of session beans. How to develop session beans. Differences between stateful and stateless session beans. Understanding EJBs. Application architectures often consist of several tiers that each has its own responsibilities. One such architecture that consists of three tiers is illustrated in the Unified Modeling Language (UML) diagram shown in Figure 1. Figure 1. The classic model of a multitiered, or layered, architecture. The two elements on the left side of the diagram in Figure 1 are called components in the UML notation. Components represent software modules. The diagram describes what is called a multitiered, or layered, architecture. Multitiered architectures have many advantages, not the least of which is the ability to change any one of the layers without affecting all of the other layers. This is in contrast to a single- tier architecture, within which all aspects of the program design coexist in a single element. Changes or actions that affect one portion of the single- tier element also potentially affect the other members of that element. Consider the three- layer architecture shown in Figure 1, consisting of user interface, application logic, and database layers. If the database layer is changed, only the application logic layer is affected. The application logic layer shields the user interface layer from changes to the database layer. This facilitates ongoing maintenance of the application and also increases the application's ability to incorporate new technologies in its layers. These layers provide an excellent model of how EJBs fit into your overall program design. EJBs provide an application logic layer and a Java. Beans- like abstraction of the database layer. The application logic layer is also known as the middle tier. Note Java. Beans and Enterprise Java. Simple Stateless Example share . This example shows how to create a Stateless session EJB using annotations. In this example we develop a simple EJB 3 Stateless session EJB. Enterprise JavaBeans (EJB) is a managed, server software for modular construction of enterprise software, and one of several Java APIs. Beans are two different things, but because of their similarities (and for marketing reasons), they share a common name. Java. Beans are components built in Java that can be used on any tier in an application. They are often thought of in relationship to servlets and as GUI components. Enterprise Java. Beans are special, server- based components, used for building the business logic and data access functionality of an application. Why use EJBs? Not too long ago, when system developers wanted to create an enterprise application, they would often start by . Some of the features of an application server include the following: Client communication: The client, which is often a user interface, must be able to call the methods of objects on the application server via agreed- upon protocols. Session state management: You'll recall our discussions on this topic in the context of JSP (Java. Server Pages) and servlet development back in Chapter 6. Transaction management: Some operations, for example, when updating data, must occur as a unit of work. If one update fails, they all should fail. Database connection management: An application server must connect to a database, often using pools of database connections for optimizing resources. User authentication and role- based authorization: Users of an application must often log in for security purposes. The functionality of an application to which a user is allowed access is often based on the role associated with a user ID. Asynchronous messaging: Applications often need to communicate with other systems in an asynchronous manner; that is, without waiting for the other system to respond. This requires an underlying messaging system that provides guaranteed delivery of these asynchronous messages. Application server administration: Application servers must be administered. For example, they need to be monitored and tuned. Building EJB 3.0 applications with WebSphere Application Server. This example uses the editor in Eclipse that you use to create JPA applications. For example, EJB 3.0 still permits XML configuration. EJB V3.0 provides a robust toolset for data persistence in Java. Using EJBs doesn't have to be hard. See how you can access these features in an eclipse environment and have stronger integration of your applications with the. How-To Develop an Entity Bean using EJB 3.0. Entity Bean example using EJB 3.0. Home > Knowledge Base > EJB3 Tutorial - EJB 3 Development for Glassfish using Eclipse 3.2 Tutorial. Aug 1, 2006 / JKB-005. EJB Create Application - Learn EJB 3.0 and 3.1. In example below, We'll create a ejb module project named Component. Creating an Enterprise Application with EJB 3.1. In the example in this tutorial you will use a single machine to host the Java EE server, the database and view the web pages. EJB Tutorial for Beginners - Learn EJB in simple and easy steps starting from basic to advanced concepts with examples including Environment Setup, Application Server, Container, Enterprise Bean, Annotations. The EJB specification. The EJB specification defines a common architecture, which has prompted several vendors to build application servers that comply with this specification. Now developers can get off- the- shelf application servers that comply with a common standard, benefiting from the competition (in areas such as price, features, and performance) among those vendors. Some of the more common commercial EJB application servers are Web. Logic (BEA), Java Enterprise System (Sun), OC4. J containers for Oracle Database 1. Web. Sphere (IBM). There are also some very good open source entries in this market such as JBoss and JOn. AS. Sun also provides an open source reference implementation (Java EE SDK) of the Java EE 5 and EJB 3. These application servers, in conjunction with the capabilities defined in the EJB specification, support all of the features listed here and many more. The EJB specification was created by experienced members of the development community; such a body is called an expert group. In the EJB specification's expert group are members from such organizations as JBoss, Oracle, and Google. Thanks to them, we now have a standard, specifications- based way to develop and deploy enterprise- class systems. We are approaching the Java dream of developing an application that can run on any vendor platform as- is. This is in contrast to the vendor- specific way we used to develop, where each server had its own way of doing things, and where the developer was locked into the chosen platform once the first line of code was written! The version of the EJB specification that is included with the Java EE 5. EJBs. The EJB 3. 0 specification has added many improvements to its predecessor (version 2. J2. EE 1. 4 recommendation), including metadata annotations to simplify deployment concerns, a higher degree of control over bean persistence, and a much more simplified (but no less powerful) programming model for developing EJBs. The three kinds of EJBs. There are actually three kinds of EJBs: session beans, entity beans, and message- driven beans. Here, we will present a brief introduction to each type of bean. The balance of this article will then focus on session beans. Note When referring to EJBs in the general sense, we'll use the term EJBs, enterprise beans, or simply beans. Session beans. One way to think about the application logic layer (middle tier) in the sample architecture shown in Figure 1 is as a set of objects that, together, implement the business logic of an application. Session beans are the construct in EJBs designed for this purpose. As shown in Figure 2, there may be multiple session beans in an application. Each handles a subset of the application's business logic. A session bean tends to be responsible for a group of related functionality. For example, an application for an educational institution might have a session bean whose methods contain logic for handling student records. Another session bean might contain logic that maintains the lists of courses and programs available at that institution. There are two types of session beans, which are defined by their use in a client interaction: Stateless: These beans do not declare any instance (class- level) variables, so that the methods contained within can act only on any local parameters. There is no way to maintain state across method calls. Stateful: These beans can hold client state across method invocations. This is possible with the use of instance variables declared in the class definition. The client will then set the values for these variables and use these values in other method calls. There may be more work involved for the server to share stateful session beans than is required to share stateless beans. Storing the state of an EJB is a very resource- intensive process, so an application that uses stateful beans may not be easily scalable. Stateless session beans provide excellent scalability, because the EJB container does not need to keep track of their state across method calls. You'll see how to develop both stateless and stateful session beans later in this article. All EJBs, session beans included, operate within the context of an EJB server, as shown in Figure 2. An EJB server contains constructs known as EJB containers, which are responsible for providing an operating environment for managing and providing services to the EJBs that are running within it. In a typical scenario, the user interface (UI) of an application calls the methods of the session beans as it requires the functionality that they provide. Session beans can call other session beans and entity beans. Figure 2 illustrates typical interactions between the user interface, session beans, entity beans, and the database. Figure 2. Session and entity beans in an application. Click on thumbnail to view full- sized image. Entity beans. Before object orientation became popular, programs were usually written in procedural languages and often employed relational databases to hold the data. Because of the strengths and maturity of relational database technology, it is now often advantageous to develop object- oriented applications that use relational databases. The problem with this approach is that there is an inherent difference between object- oriented and relational database technologies, making it less than natural for them to coexist in one application. The use of entity beans is one way to get the best of both of these worlds, for the following reasons: Entity beans are objects, and they can be designed using object- oriented principles and used in applications as objects. EJB V3. 0 database persistence with Eclipse. Introduction. One thing that. There is all kinds of data from all kinds of resources. On one hand. this makes applications richer than ever. On the other hand, all of this. It becomes even more complicated if. In a Java. environment, EJBs have emerged as a way to reliably persist while. EJB V3. 0 has continued that evolution, bringing more tools and. Working with EJBs doesn't have to be hard. With. Eclipse and some basic concepts, you can harness their power in your. EJB V3. 0. EJB V3. EJBs with an annotations- based API. Developing. Entity EJBs requires a Java IDE, an application server, and a relational. Web. Sphere V6. x requires the Web. Sphere Application Server V6. Feature Pack to create EJB V3. Web. Sphere V7 has built- in. EJB V3. 0. The Eclipse IDE is the most. Java IDE. In this article, we'll develop an EJB. V3. 0 entity bean using the Eclipse- IBM Web. Sphere 7- IBM DB2 9. The EJB V3. 0 specification in Web. Sphere is backed with Java. Persistence API (JPA) for persistence. JPA is further based on other. Hibernate, JDO, and Top. Link. JPA is a POJO. API for object- relational mapping and makes use of metadata. Java objects and a relational. JPA supports a SQL- like language for static and dynamic. JPA is integrated into the JSR 2. Enterprise Java. Beans V3. Trial versions of Web. Sphere application server and DB2 database were used. Community editions of. Web. Sphere Application Server and DB2. The trial version of. Web. Sphere Application Server includes free support. Support for the Community edition of Web. Sphere Application Server. Back to top. Preliminary setup. Download and install Web. Sphere Application Server V7 (see Resources). Download and install Eclipse IDE for Java EE Developers (see Resources). Download and install DB2 V9. Resources). Create database instance SAMPLE in DB2. Back to top. Configuring. Web. Sphere with DB2. Start the Web. Sphere Application Server. At. the First Steps Console, select Start the server. The Web. Sphere. server is initiated, as shown in Figure 1. Starting. Web. Sphere V7 Application Server. Next, start the Administrative Console/Integrated Solutions Console by. Administrative Console link. In the Integrated. Solution Console window, select. Resources > JDBC > JDBC > New in the JDBC providers. Figure 2. Creating a new. JDBC provider. In the Create a new JDBC Provider window, select. Database > DB2, Provider > DB2 Universal. JDBC Driver Provider, and Implementation > Connection. Next, as shown in Figure 3. Setting. configuration values. The Summary page lists the summary of the JDBC. A new JDBC provider is added. JDBC providers table. Select the new. JDBC provider, and click Save to store the JDBC provider to the. Figure 4. New JDBC. Prior to configuring a data source, a J2. EE connector authentication data. J2. EE connector authentication data entries are used by. JDBC data sources to log in to a database. Select the Security > Global. Integrated Solutions Console. Next, select. the Java Authentication and Authorization Service > J2. C. authentication data link in the Authentication subheader, as shown in Figure 5. Creating J2. C. authentication data. In the table of user identities and passwords, click New. In the new. header, specify a user alias in the Alias. User Id, which is the login ID for the. DB2 database, and the password to login to the DB2 database, as shown in. Figure 6. Figure 6. Specifying J2. C. Click Save to store the J2. C authentication data entry to the master. A DB2 database login alias is added to the J2. C. authentication data table, as shown in Figure 7. New J2. C. authentication data. To configure a JDBC data source, select the JDBC provider previously. In the DB2 Universal JDBC Provider. Datasources link, as shown in Figure 8. The JNDI. name shall be used in the persistence. EJB V3. 0 entity bean, which will be created later. Creating a. data source. Specify the data source- specific properties for the data source. Select. Driver Type > 4, Database Name > SAMPLE. Server Name > localhost, and Port. Number > 5. 00. Click Next, as shown in Figure 1. Specifying. data- source properties. To select the J2. C authentication data for the data source, choose the. Click Next, as shown in Figure. Setting. the security alias. In the Summary page for the data source, select. Finish. A new data source is added to the table. Click. Save to store the data source to the master configuration. The data. source connection test will indicate whether the test is successful, as. Figure 1. 2. Testing. Back to top. Creating a DB2. Access the DB2 database from a command- line. Command Editor or the Command Line Processor. To create a. database table in the default sample database SAMPLE, run the following. SQL script. This creates a Catalog table for. EJB V3. 0 entity. CREATE TABLE Catalog (id INT PRIMARY KEY NOT NULL. VARCHAR(1. 00), publisher VARCHAR(1. VARCHAR(1. 00). title VARCHAR(1. VARCHAR(1. 00)); Back to top. Creating an EJB V3. Eclipse. In Eclipse IDE, select File > New > Project. In the New Project window, select. EJB > EJB Project > Next. In the New EJB Project window, specify a. EJB3. Entity. Bean, for example). Select EJB Module. Version > 3. 0 > Next. In the EJB Module window, select the default Source. Folder > ejb. Module > Finish. Next, add an entity bean Java class to the EJB V3. Select. File > New > Other and in the New window, select. Java > Class > Next. In the New Java Class window, the Source. EJB3. Entity. Bean/ejb. Module by. default. Specify a package name (com. Catalog), then click. Finish. An entity bean Java class is added to the EJB V3. Web. Sphere. V7 requires JDK V6. If not already installed, install JDK V6 (see Resources). Right- click on EJB. Properties and select the Java Build Path. Add the JRE System Library . Create. a library EJB3 and add j. Figure 1. 3. Figure 1. Libraries in. the Java Build Path. Add the source folder ejb. Module to the Java. Build Path, as shown in Figure 1. Source folder. in Java Build Path Similar to adding the Catalog. Java classes Catalog. Test. Bean. java (the. Catalog. Test. Local. Catalog. Test. Remote. An EJB V3. 0 entity bean is required to have a. META- INF directory. In the Project Explorer, select. META- INF > File > New > Other. In the New window, select. XML > XML > Next. In the New XML File window, select the. Module > META- INF folder. Specify File. Name > persistence. Finish. A persistence. META- INF folder. Create a build. xml script in the EJB V3. File > New > Other > XML > XML. Create a META- INF folder in the project folder, and. Create a web. Module folder to the project. JSP client to the entity EJB, and add. EJB3. Client. jsp to the folder. Add a WEB- INF folder to the web. Module folder, and add a web. WEB- INF folder. The directory. EJB V3. 0 project is shown in Figure 1. Directory. structure of EJB V3. Back to top. Creating an EJB. V3. 0 entity bean Unlike EJB V2. EJB V3. 0 entity beans are. Plain Old Java Objects (POJOs). Entity- bean mappings are defined using. JDK V5 and are in the javax. A POJO class annotated. Entity annotation is an entity bean. If the @Table annotation is not specified, the default. We shall create an entity bean. Catalog that is mapped to Catalog table. Therefore, an. entity bean is recommended to implement the java. Serializable interface. In the entity- bean class. POJO properties. Also specify the serial. Version. UID, which is used by the serialization runtime. Add the getter. and setter methods for the entity bean properties. Specify the identifier. Id annotation. There are. EJB V3. 0 annotations, which may be specified in an entity bean. Resources). The Catalog entity bean is shown. Listing 1. Listing 1. Entity- bean class. Catalog. javaimport java. Serializable. import javax. Table(name=. The persistence- unit is required to be named. A JDBC data source. JNDI jdbc/DB2. DS in the Web. Sphere V7 application server was previously. Specify the JNDI name in the jta- data- source element in persistence. The default JPA persistence provider in Web. Sphere Application Server V7 is a version of the Apache Open. JPA provider. Copy Listing 2 to the. Eclipse. Configuration file. Use a stateless session bean, which consumes lesser. A. stateless session bean class is annotated with the @Stateless annotation. The stateless session bean class Catalog. Test. Bean implements the Catalog. Test. Local and Catalog. Test. Remote interfaces. Use the Entity. Manager API to create, find, query, and remove entity. Inject an Entity. Manager using the. Persistence. Context. Persistence. Context. Entity. Manager em; A session bean deployed to the Web. Sphere server with JNDI binding Session. For convenient access to the. JNDI name from a JSP client, assign public static. JNDI name. Use the test() method to create and persist entity. Entity. Manager object, which was. Injecting an Entity. Manager implies that an instance of Entity. Manager is made available to the session. Create an instance of the entity bean. Catalog catalog = new Catalog(new Integer(1), . Next, create a query using the create. Query method of the Entity. Manager object. The string is specified as an EJB- QL. Execute and return the result as a List. Result. List() method. As an. example, select the catalog entry corresponding to author Elliotte Rusty. Harold. List catalog. Entry = em. create. Query(. Subsequently, create and run a query to list. The session. bean class Catalog. Test. Bean is shown in Listing. Listing 3. Session bean. Catalog. Test. Bean. Iterator. import java. List. import javax. Stateless. import javax. Entity. Manager. import javax. Persistence. Context. Catalog. Test. Bean implements Catalog. Test. Remote, Catalog. Test. Local . Remote and local interfaces. Remote. public interface Catalog. Test. Remote . Next, a test client JSP EJB3. Client. jsp is created in which the test() of the session bean is run. To create an instance of Catalog. Test. Local using JNDI lookup, first create an Intial. Context object. Obtain a Catalog. Test. Local instance using JNDI lookup in.
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