ejb fundamentals q

7/30/2019 EJB Fundamentals q

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EJB Fundamentals

Swapnil Shrivastava



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 businessapplications.

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

secure. These applications may be write once, and

then deployed on any server platform thatsupports the EJB specification.




Short Definition EJB is a server-side component

architecture that simplifies the process

of building enterprise-class distributedcomponent 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 anapplication.

Consists of one or more java objects.




Types of Beans Session Bean

Entity 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:



Entity Bean Entity Bean Models business data.

They are like ‘nouns’ because they aredata objects

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

Session beans typically calls entitybeans to perform business goals.



Message Driven Bean Message driven beans are similar to

session beans.

They are actions.

They are called only when they receivesome message.

E.g. : stock trade message.



EJB Architecture

EJB MessageDriven Bean

EJB Session

BeanEJB Entity

Bean

EJB SessionBean

EJB Session

Bean

EJB SessionBean

Servlet JSP

Messaging

Client

C/C++

Client

Java Applet

Java Appl

Business

Partner System

HTML

Client

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

HTTPFirewall SOAP,UDDI

WSDL,ebXML

WebServer

Application Server

PresentationTier

Business

Tier



EJB Foundation: Distributed

Objects

Client

Skeleton

Distributed

Object

Stub

Network

Remote Interface

Remote Interface



What do we need to worryabout now?

We take a monolithic application andbreak it into distributed system with

multiple clients connecting to multipleservers 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

SystemManagement

Message OrientedMiddleware

And many more….. Middleware




Explicit Middleware

Client

Skeleton

Distributed

Object

Stub

Network

Remote Interface

Remote

Interface

Transaction

Services

Security

Services

Database

drivers

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

Transaction

Services

Security

Services

Database

drivers

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 themremotely.

It intercepts the client request and delegatesthem 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 localaccess.

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 beanclass 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 toRMI rules.




Home Object EJB object factory.

Creates,finds and destroys EJB objects.

Proprietary and specific to each EJBcontainer.

Home objects implements HomeInterface.




Home Interface EJB Object factory interface.

They define methods for

creating,destroying and finding EJBObjects.

All home interfaces must extend

javax.ejb.EJBHome. EJB remote interfaces must confirm to

RMI rules.




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.




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

Remote

Interface

Local

Interface

Enterprise

Bean

Home

Interface

Deployment

Descriptor

Vendor

Specific

Jar file creator EJB jar file




Sample ApplicationMy First Bean!




Session Bean : FirstBean package 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 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(“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 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




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 EJBObject Reference

6: Invoke Business

Method

7: Delegate Request to Bean

Remote

Interface

Home

Interface

EJB Container




Advantages of EJB Helps to write scalable,reliable and secure

applications.

Provides distributed component framework and hence supports rapid applicationdevelopment.

Supports application portablility and

reusability across any vendor’s enterprisemiddleware services.

It is agreed upon by industry.



References Mastering Enterprise Java Beans

J2EE 1.4 Tutorials

Professional Java Server Programming,J2EE Edition

ejb fundamentals q

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