ejb basics

8/9/2019 EJB Basics

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EJB Fundamentals

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Contents Introduction

Technology Overview EJB Architecture

EJB Specification

Sample Application

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Suns Definition EJB architecture is a component architecture

f or the development and deployment of

component based distributed businessapplications.

Applications written using EJB architectureare scalable, transactional, and multi-user

secure. These applications may be write once, and

then deployed on any server platf orm that supports the EJB specification.

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Short Definition EJB is a server-side component

architecture that simplifies the processof building enterprise-class distributedcomponent applications in Java.

EJB provides standard f or component

architecture.

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Enterprise Bean Server side software components that

can be deployed in distributed multi tierenvironment.

They encapsulate business logic of anapplication.

Consists of one or more java objects.

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Types of Beans Session Bean

Entit y Bean Message driven Bean

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Session Bean Session beans model business

processes.

They are like verbs because they areactions.

E.g. billing engine, catalog engine etc:

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Entit y Bean Entit y Bean Models business data.

They are like nouns because they aredata objects

E.g. product, an order, an employeeetc:

Session beans t ypically calls entit y beans t o perf orm business goals.

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Message Driven Bean Message driven beans are similar t o

session beans.

They are actions.

They are called only when they receivesome message.

E.g. : st ock trade message.

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EJB Architecture

EJB MessageDriven Bean

EJB Session

BeanEJB Entity

Bean

EJB SessionBean

EJB Session

Bean

EJB SessionBean

Servlet JSPMessaging

Client

C/C++

Client

Java Applet

Java Appl

BusinessPartner System

HTMLClient

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

HTTPFirewall SOAP,UDDI

WSDL,ebXML

WebServer

Application Server

Presentation

Tier

Business

Tier

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EJB Foundation: Distributed

Objects

Client

Skeleton

Distributed

Object

Stub

Network

Remote Interface

Remote Interface

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What do we need t o worry about now?

We take a monolithic application andbreak it int o distributed system withmultiple clients connecting t o multipleservers and databases over network.

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Services Remote Method

Invocation

Load Balancing Transparent Fail Over

Back end integration.

Clustering

Dynamic Re deployment

Object life cycle

Caching

Securit y Resource Pooling

SystemManagement

Message OrientedMiddleware

And many more..Middleware

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Explicit Middleware

Client

Skeleton

Distributed

Object

Stub

Network

Remote Interface

Remote

Interface

Transaction

Services

SecurityServices

Database

drivers

Database API

Security API

Transaction API

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Example Bank account obj Transfer(Acct acc1, Acct acc2,long amt)

//1.Call middleware API t o perf orm securit y

check.

//2.Call middleware API t o start a trans

//3.Call middleware API t o load rows from db.

//4.perf orm trans. //5.Call middleware API t o st ore rows in db

//6.Call middleware API t o end the trans.

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Explicit Middleware Difficult t o Write.

Difficult t o Maintain. Difficult t o Support.

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Implicit MiddlewareClient

Skeleton

Request

Interceptor

Stub

Network

Remote Interface Remote

Interface

Transaction

Services

Security

Services

Database

drivers

Database API

Security API

Transaction API

Distributed

ObjectRemote

Interface

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Example Bank account obj Transfer(Acct acc1,Acct acc2,long amt)

//1. Perf orm trans.(subtract bal from oneaccount and add t o other).

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Implicit Middleware Easy t o Write.

Easy t o Maintain. Easy t o Support.

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EJB Container House enterprise bean and makes them

available t o the client t o invoke them

remotely. It intercepts the client request and delegates

them t o corresponding bean class.

It aut omatically perf orms implicit middleware

that the distributed object needs. EJB object is the physical part of the

container.

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EJB Component Ingredients Enterprise Bean Class

Interfaces Remote and Home interface f or remote

access.

Local and Local Home interface f or localaccess.

Deployment Descript or.

Vendor Specific files.

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Enterprise Bean Class It conf orms t o a well defined interface.

It contains business implementationdetails of our component.

Each bean t ype has more specificinterface that extends

javax.ejb.EnterpriseBean interface. Bean class implements the interface

corresponding t o the bean t ype.

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EJB Object Client request intercept or.

It duplicates all the business logicmethods that the corresponding beanclass exposes.

Proprietary and specific t o each EJB

container.

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Remote Interface Interface t o request intercept or.

Inf orms EJB Object aut

o generat

or

which methods t o clone.

All remote interfaces must derive from javax.ejb.EJBObject.

EJB remote interfaces must confirm t o RMI rules.

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Home Object EJB object fact ory.

Creates,finds and destroys EJB objects.

Proprietary and specific t o each EJBcontainer.

Home objects implements HomeInterface.

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Home Interface EJB Object fact ory interface.

They define methods f orcreating,destroying and finding EJBObjects.

All home interfaces must extend

javax.ejb.EJBHome.

EJB remote interfaces must confirm t o RMI rules.

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Local Access

Local objects make enterprise bean calls

fast and efficient. Local objects implements Local Interface.

Local home objects creates beans fast.

Local home object implemnts Local Homeinterface.

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Deployment Descript or Declare how the container should

perf orm middleware services f or the

EJB component.

In EJB 2.0 deployment descript or is aXML file.

Key t o implicit middleware.

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Vendor Specific Files All vendors have proprietary value

added features.

Include files specific t o that vendor.

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Package

Remote

Interface

Local

Interface

Enterprise

Bean

Home

Interface

Deployment

Descriptor

Vendor

Specific

Jar file creator EJB jar file

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Sample ApplicationMy First Bean!

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Session Bean : FirstBean package example;

public class FirstBean implements javax.ejb.SessionBean

{

private SessionContext ctx;

public void ejbCreate(){

System.out.println(³ejbCreate()´);

}

public void ejbRemove()

{

System.out.println(³ejbRemove()´);

}

public void ejbActivate()

{

System.out.println(³ejbActivate()´);

}

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public void ejbPassivate()

{

System.out.println(³ejbPassivate()´);

}

public void setSessionContext(javax.ejb.SessionContext ctx)

{

this.ctx=ctx;

}

public String first(){

System.out.println(³first()´);

return ³My First Bean´;

}

}

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Remote Interface : First.java package example;

public interface First extends javax.ejb.EJBObject{

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

}

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Home Interface : FirstHome package example;

public interface FirstHome extends javax.ejb.EJBHome

{First create() throws java.rmi.RemoteException,

javax.ejb.CreateException;

}

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Deployment Descript or<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>

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Client Application package 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(³FirstHome´);

FisrtHome home=(FirstHome)

javax.rmi.RemotePortableObject.narrow

(obj,FirstHome.class);

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First first=home.create();

System.out.println(first.first());

first.remove();

}

}

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EJB Object Model<<interface>>

java.rmi.Remote

<<interface>>

java.io.Serializable

<<interface>>

javax.ejb.EnterpriseBean

<<interface>>

javax.ejb.SessionBean

Bean Implement

Class

<<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

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Home

Object

EJB

Object

Enterprise

Bean

Client

Naming

Service

1 : Retrieve

Home object

Reference

2 : Return

Home object

Reference

JNDI

3: Create a new

EJB Object

4: Create a new

EJB Object

5: Return EJB

Object Reference

6: Invoke Business

Method

7: Delegate Request to Bean

Remote

Interface

Home

Interface

EJB Container

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Advantages of EJB Helps t o write scalable,reliable and secure

applications.

Provides distributed component frameworkand hence supports rapid applicationdevelopment.

Supports application portablilit y and

reusabilit y across any vendors enterprisemiddleware services.

It is agreed upon by industry.

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References Mastering Enterprise Java Beans

J2EE 1.4 Tut orials

Professional Java Server Programming,J2EE Edition

ejb basics

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