11 Copyright © 2005, Oracle. All rights reserved. Creating the Business Tier: Enterprise JavaBeans.

11Copyright © 2005, Oracle. All rights reserved.

Creating the Business Tier: Enterprise JavaBeans

11-2 Copyright © 2005, Oracle. All rights reserved.

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


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


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.


Types of EJBs

EJB Type Purpose

Session Beans Performs a task for a client

Entity Beans Represents a business object that exists in a database

Message-Driven Beans Receives asynchronous Java Message Service (JMS) messages


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

Client 1

Client 2

Pool of SLSBs

EJB container

Client 1

Client 2

SFSBs


Entity BeansEntity 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).


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

Clients

EJB container

Pool of MDBs

JMS queue


EJB Architecture

EJB client

EJB server

Enterprise ServicesNaming, Transaction, Security,

Messaging

Deployment

descriptor

Database

EJB container

Remote/local

object

Home/local home

object

Remote/ local

interface

Home/local home

interfaceEJB

Class


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


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

Client

EJB container

EJBclass

home/local home object

Home/local home

interfaceContainer generated

remote/local

object

Remote/ local

interface


Services Provided by the EJB Container

• Life-cycle management

• Bean instance pooling

• Client state management

• Database connection pooling

• Declarative transaction management

• Security

• Persistence


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


EJB Interfaces and Classes

• Interfaces: – Remote interface/Local interface– Home interface/Local home interface

• Classes:– Bean class– Primary key class (entity beans)


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.


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


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.


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


The EJB Deployment Process

Jar command/

tool

EJB JAR

JNDI

Component deployer’s responsibility

Developer’sresponsibilityHome interface

Remote interfaceBean class

Other classes

Deploymentdescriptor

Deploymenttools/

commands

Deployed EJB in the Server


<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>

ejb-jar.xml File


orion-ejb-jar.xml File

Oracle Application Server 10g uses theorion-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


Creating an EJB in JDeveloper


Using the EJB Wizard


Using the EJB Wizard


Adding Methods to the Bean

To add methods to the bean, right-click and select Go To Bean Class:


Deploying to Oracle Application Server 10g from JDeveloper


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


Practice 11-1: Overview

This practice covers the following topics:

• Creating an EJB in JDeveloper

• Testing an EJB

11 Copyright © 2005, Oracle. All rights reserved. Creating the Business Tier: Enterprise JavaBeans.

Documents

beans slide

state ejb container

ejb components

ejb interfaces

ejb classes

enterprise beans

client entity beans

session beans session