Enterprise JavaBeans: Fundamentals. EJB Fundamentals(c)CDAC(Formerly NCST)2 Contents Introduction...

Enterprise JavaBeans: Fundamentals

EJB Fundamentals (c)CDAC(Formerly NCST) 2

Contents Introduction Technology Overview EJB Architecture EJB Specification Sample Application


Sun’s Definition EJB architecture is a component

architecture for the development and deployment of component based distributed business applications.

Applications written using EJB architecture are scalable, transactional, and multi-user secure.

These applications may be write once, and then deployed on any server platform that supports the EJB specification.


Short Definition EJB is a server-side component

architecture that simplifies the process of building enterprise-class distributed component applications in Java.

EJB provides standard for component architecture.


Enterprise Bean Server side software components

that can be deployed in distributed multi tier environment.

They encapsulate business logic of an application.

Consists of one or more java objects.


Types of Beans Session Bean Entity Bean Message driven Bean


Session Bean Session beans model business

processes. They are like ‘verbs’ because they

are actions. E.g. billing engine, catalog engine

etc:


Entity Bean Entity Bean Models business data. They are like ‘nouns’ because they

are data objects E.g. product, an order, an

employee etc: Session beans typically calls entity

beans to perform business goals.


Message Driven Bean Message driven beans are similar

to session beans. They are actions. They are called only when they

receive some message. E.g. : stock trade message.


EJB Architecture

EJB MessageDriven Bean

EJB SessionBean

EJB EntityBean

EJB SessionBean

EJB SessionBean

EJB SessionBean

Servlet JSPMessaging

ClientC/C++Client

Java AppletJava Appl

BusinessPartner System

HTML Client

Messaging CORBA-IIOP RMI-IIOP RMI-IIOP RMI-IIOP

HTTPFirewall SOAP,UDDIWSDL,ebXML

WebServer

Application Server

PresentationTier

BusinessTier


EJB Foundation: Distributed Objects

Client

Skeleton

DistributedObject

Stub

Network

Remote InterfaceRemote Interface


What do we need to worry about now?

We take a monolithic application and break it into distributed system with multiple clients connecting to multiple servers and databases over network.


Services Remote Method

Invocation Load Balancing Transparent Fail

Over Back end integration. Clustering Dynamic Re

deployment

Object life cycle Caching Security Resource Pooling System

Management Message Oriented

Middleware And many more…..

Middleware


Explicit Middleware

Client

Skeleton

DistributedObject

Stub

Network

Remote InterfaceRemote Interface

TransactionServices

SecurityServices

Databasedrivers

Database API

Security API

Transaction API


Example – Bank account obj Transfer(Acct acc1, Acct acc2,long amt)//1.Call middleware API to perform security

check.//2.Call middleware API to start a trans//3.Call middleware API to load rows from db.//4.perform trans.//5.Call middleware API to store rows in db//6.Call middleware API to end the trans.


Explicit Middleware Difficult to Write. Difficult to Maintain. Difficult to Support.


Implicit MiddlewareClient

Skeleton

RequestInterceptor

Stub

Network

Remote Interface Remote Interface

TransactionServices

SecurityServices

Databasedrivers

Database API

Security API

Transaction API

DistributedObject

Remote Interface


Example – Bank account obj Transfer(Acct acc1,Acct acc2,long

amt)//1. Perform trans.(subtract bal from

one account and add to other).


Implicit Middleware Easy to Write. Easy to Maintain. Easy to Support.


EJB Container House enterprise bean and makes them

available to the client to invoke them remotely.

It intercepts the client request and delegates them to corresponding bean class.

It automatically performs implicit middleware that the distributed object needs.

EJB object is the physical part of the container.


EJB Component Ingredients Enterprise Bean Class Interfaces

Remote and Home interface for remote access.

Local and Local Home interface for local access.

Deployment Descriptor. Vendor Specific files.


Enterprise Bean Class It conforms to a well defined

interface. It contains business implementation

details of our component. Each bean type has more specific

interface that extends javax.ejb.EnterpriseBean interface.

Bean class implements the interface corresponding to the bean type.


EJB Object Client request interceptor. It duplicates all the business logic

methods that the corresponding bean class exposes.

Proprietary and specific to each EJB container.


Remote Interface Interface to request interceptor. Informs EJB Object auto generator

which methods to clone. All remote interfaces must derive

from javax.ejb.EJBObject. EJB remote interfaces must

confirm to RMI rules.


Home Object EJB object factory. Creates,finds and destroys EJB

objects. Proprietary and specific to each

EJB container. Home objects implements Home

Interface.


Home Interface EJB Object factory interface. They define methods for

creating,destroying and finding EJB Objects.

All home interfaces must extend javax.ejb.EJBHome.

EJB remote interfaces must confirm to RMI rules.


Local AccessLocal objects make enterprise bean calls

fast and efficient.Local objects implements Local Interface.Local home objects creates beans fast.Local home object implements Local Home

interface.


Deployment Descriptor Declare how the container should

perform middleware services for the EJB component.

In EJB 2.0 deployment descriptor is a XML file.

Key to implicit middleware.


Vendor Specific Files All vendors have proprietary value

added features. Include files specific to that

vendor.


Package

RemoteInterface

LocalInterface

EnterpriseBean

HomeInterface

DeploymentDescriptor

VendorSpecific

Jar file creator EJB jar file


Sample ApplicationMy First Bean!


Session Bean : FirstBeanpackage example;public class FirstBean implements javax.ejb.SessionBean{

private SessionContext ctx;

public void ejbCreate() {System.out.println(“ejbCreate()”);

} public void ejbRemove() {

System.out.println(“ejbRemove()”);}public void ejbActivate() {

System.out.println(“ejbActivate()”);}


public void ejbPassivate(){

System.out.println(“ejbPassivate()”);}public void setSessionContext(javax.ejb.SessionContext ctx){

this.ctx=ctx;}public String first(){

System.out.println(“first()”);return “My First Bean”;

}}


Remote Interface : First.java

package example;

public interface First extends javax.ejb.EJBObject{

public String first() throws java.rmi.RemoteException;}


Home Interface : FirstHome

package example;

public interface FirstHome extends javax.ejb.EJBHome{

First create() throws java.rmi.RemoteException,javax.ejb.CreateException;

}


Deployment Descriptor<ejb-jar>

<enterprise-bean><session> <ejb-name>First</ejb-name> <home>example.FirstHome</home> <remote>example.First</remote> <ejb-class>example.FirstBean<ejb-class> <session-type>Stateless</session-type> <transaction-type>Container</transaction-type></session>

</enterprise-bean></ejb-jar>


Client Applicationpackage example;

import javax.naming.*;Import java.util.*;

public class FirstClient{public static void main(String[] arg) throws Exception{

Properties props=System.getProperties();Context ctx=new InitialContext(props);Object obj=ctx.llokup(“FirstHome”);FisrtHome home=(FirstHome)javax.rmi.RemotePortableObject.narrow(obj,FirstHome.class);


First first=home.create();System.out.println(first.first());first.remove();

}}


EJB Object Model<<interface>>

java.rmi.Remote<<interface>>

java.io.Serializable

<<interface>>javax.ejb.EnterpriseBean

<<interface>>javax.ejb.SessionBean

Bean ImplementClass

<<interface>>javax.ejb.EJBObject

<<interface>>Javax.ejb.EJBHome

<<interface>>Remote Interface

<<interface>>Home Interface

EJB Object Home Object

Comes with Java2 platform

Comes with EJB Distribution

Written by developer

Generated by Componet Vendor Tool


HomeObject

EJBObject

EnterpriseBean

Client

NamingService

1 : Retrieve Home objectReference

2 : Return Home objectReference

JNDI

3: Create a newEJB Object

4: Create a newEJB Object

5: Return EJB Object Reference

6: Invoke BusinessMethod

7: Delegate Request to Bean

RemoteInterface

HomeInterface

EJB Container


Advantages of EJB Helps to write scalable,reliable and

secure applications. Provides distributed component

framework and hence supports rapid application development.

Supports application portablility and reusability across any vendor’s enterprise middleware services.

It is agreed upon by industry.


References Mastering Enterprise Java Beans J2EE 1.4 Tutorials Professional Java Server

Programming, J2EE Edition

Enterprise JavaBeans: Fundamentals. EJB Fundamentals(c)CDAC(Formerly NCST)2 Contents Introduction...

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