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Mastering Enterprise JavaBeans for Business Solutions

Understand the architecture and types of EJBs, deployment steps, and when to utilize EJBs in complex applications. Learn about sessions, entities, MDBs, and the EJB container services for effective business logic encapsulation. Explore EJB client interactions and interfaces for scalable and portable development.

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Mastering Enterprise JavaBeans for Business Solutions

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  1. Creating the Business Tier: Enterprise JavaBeans

  2. Objectives • After completing this lesson, you should be able to do the following: • Define an Enterprise JavaBean • Describe the Enterprise JavaBeans (EJB) architecture • Describe the types of EJBs and when they are used • Explain EJB interfaces • Define the steps to deploy an EJB to Oracle Application Server 10g

  3. Enterprise JavaBeans (EJB) • Enterprise JavaBeans are portable components, which: • Enable faster application development • Allow reuse of business components • Encapsulate business logic that can be invoked by clients • Execute in a container that provides services such as support for transactions, persistence, and access control for the beans

  4. When to Use EJBs • When developing a J2EE application, decide whether to use EJBs based on the following requirements: • The applications are complex and would benefit from the system-level services that are provided by an EJB container. • The applications must be portable and scalable. • The applications must be accessed by different types of clients.

  5. Types of EJBs EJB Type Purpose Session Beans Performs a task for a client Represents a business object that exists in a database Entity Beans Receives asynchronous Java Message Service (JMS) messages Message-Driven Beans

  6. Session Beans • Session beans invoke methods for a single client. There are two types of session beans: • Stateless Session Beans (SLSBs) • Conversation that spans a single method call • Single request business processes that do not maintain client-specific state • Stateful Session Beans (SFSBs) • Conversation with one client that may invoke many methods • Business processes that span multiple method requests, thus maintaining state EJB container EJB container Pool of SLSBs SFSBs Client 1 Client 1 Client 2 Client 2

  7. Entity Beans • Entity beans represent a business object in the database. They are: • Sharable across multiple clients • Uniquely identifiable through a primary key • Persistent—the state survives an EJB server crash • There are two types of persistence in entity EJBs: • Container-managed persistence (CMP) beans: • The state of the bean is maintained by the container. • The bean developer specifies the persistent fields. • Bean-managed persistence (BMP) beans: • The state of the bean is maintained by the bean itself. • The bean developer writes the logic to manage persistence by using Java Database Connectivity (JDBC).

  8. Message-Driven Beans • Provide a facility for asynchronous communication • Exist within a pool, and receive and process incoming messages from a JMS queue or topic • Are invoked by the container to handle each incoming message from the queue or topic • Are similar to stateless session beans JMS queue EJB container Clients Pool of MDBs

  9. EJB Architecture EJB server EJB container Home/local home interface Home/local home object EJB Class EJB client Remote/local object Remote/ local interface Database Enterprise Services Naming, Transaction, Security, Messaging Deployment descriptor

  10. EJB Server • Manages the EJB container • Provides a deployment and execution platform for EJB components • Provides system services to containers that in turn provide services to beans: • Transaction services • JNDI naming services • Can provide vendor-specific features such as connection pooling

  11. EJB container Home/local home interface home/local home object EJB class Container generated Client remote/local object Remote/ local interface EJB Container • Manages the life cycle of the enterprise beans • Isolates the enterprise beans from direct access by client applications • Makes required services available to the EJB classes through well-defined interfaces

  12. Services Provided by the EJB Container • Life-cycle management • Bean instance pooling • Client state management • Database connection pooling • Declarative transaction management • Security • Persistence

  13. EJB Client • An EJB client is a stand-alone application, servlet, JSP, or another EJB that accesses the bean. It can be a: • Local client: • Resides within the same Java virtual machine (JVM) as the bean • Passes arguments by reference to the bean • Interacts with the EJB through methods defined in the local interface • Remote client: • Is location independent • Passes arguments by value to the bean • Interacts with the EJB through methods defined in the remote interface

  14. EJB Interfaces and Classes • Interfaces: • Remote interface/Local interface • Home interface/Local home interface • Classes: • Bean class • Primary key class (entity beans)

  15. Remote Interface and Remote Object • Remote interface: • Extends the javax.ejb.EJBObject interface that extends the java.rmi.Remote interface • Describes the client view of an EJB • Declares the business methods that are accessible to remote clients • EJB object: • Is a container-generated implementation of a remote interface • Is a reference object that a client receives • Delegates the method calls to a bean class after doing some infrastructure work • The remote interface and remote object are used by session and entity beans.

  16. Home Interface and Home Object • Home interface: • Extends the javax.ejb.EJBHome interface that extends the java.rmi.Remote interface • Contains the life-cycle methods for creating, removing, and locating the instances of a bean class • Contains home methods • Are accessed by remote clients • Home object: • Is a container-generated implementation of the home interface • Uses callback methods on a bean class to perform its functions

  17. Local Interface and Local Home Interface • Local interface: • Extends the javax.ejb.EJBLocalObject interface • Declares the business methods of the bean that are accessible by a local client • Improves performance because the bean resides in the same JVM, and parameters are passed by reference • Local home interface: • Extends the javax.ejb.EJBLocalHome interface • Defines the life-cycle methods that are accessible by local clients • These interfaces are used by session and entity beans. • They enable relationships between entity beans.

  18. EJB Bean Class • A bean class extends javax.ejb.EnterpriseBean. • A session/entity bean class: • Implements javax.ejb.SessionBean / javax.ejb.EntityBean • Implements business/life-cycle methods • Contains methods to support container callbacks • Contains methods to set and unset the context of the bean • A message-driven bean class: • Implements javax.ejb.MessageDrivenBean • Must implement the MessageListener interface • Contains business logic in the onMessage() method

  19. The EJB Deployment Process Developer’sresponsibility Home interface Remote interface Bean class Other classes Component deployer’s responsibility Deployment descriptor EJB JAR Deployment tools/ commands Jar command/ tool Deployed EJB in the Server JNDI

  20. ejb-jar.xml File <ejb-jar> <enterprise-beans> <session>|<entity>|<message-driven> <description>Say Hello</description> <display-name>HelloWorld</display-name> <ejb-name>HelloWorld</ejb-name> <home>lesson11.HelloWorldHome</home> <remote>lesson11.HelloWorld</remote> <ejb-class>lesson11.impl.HelloWorldBean</ejb-class> </session>|</entity>|</message-driven> </enterprise-beans> <assembly-descriptor> <security-role> </security-role> <method-permission> </method-permission> <container-transaction> </container-transaction> </assembly-descriptor> </ejb-jar>

  21. orion-ejb-jar.xml File • Oracle Application Server 10g uses the orion-ejb-jar.xml file for deployment. This file: • Specifies run-time attributes of the bean for deployment to the container • Enables customization of the run-time behavior of enterprise beans

  22. Creating an EJB in JDeveloper

  23. Using the EJB Wizard

  24. Using the EJB Wizard

  25. Adding Methods to the Bean • To add methods to the bean, right-click and select Go To Bean Class:

  26. Deploying to Oracle Application Server 10g from JDeveloper

  27. Summary • In this lesson, you should have learned how to: • Define an EJB • Describe the EJB architecture • Describe the types of EJBs and when they are used • Explain EJB interfaces • Define the steps to deploy an EJB to Oracle Application Server 10g

  28. Practice 11-1: Overview • This practice covers the following topics: • Creating an EJB in JDeveloper • Testing an EJB

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