Tutorial EJB

8/2/2019 Tutorial EJB

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Tutorial on Enterprise JavaBeans(EJB)

Yi Liu

Department of Computer and Information Science

University of Mississippi


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Contents

Part I Introduction to EJB component model

Part II Three Enterprise beans typesEntity Beans

Session Beans

Message-driven Beans

Part III J2EE deploytool demonstration


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Part I

Introduction to EJB ComponentModel


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What is Enterprise JavaBeans ?

Component model for building server-

side, enterprise-class applications.


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EJB Model

EJB Client

EJB Client

EJB Client

. . .Enterprise Bean

Enterprise Bean

EJB Container

EJB Server


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EJB Container

Exists on the server-side

Forms core of EJB component model

implementation

Provides EJB objects a runtime environment

remote access to the bean

security, persistence

transactions, concurrency

access to and pooling of resources


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Enterprise Beans

Encapsulate business logic in reusable,

serverside components

Are deployed and executed within EJB

container , never directly accessed from

outside container.

Are accessed and executed by clients viaEJB container


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Part II

Three Enterprise Beans Types


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Three Types of Enterprise Beans

Session Beans

Entity Beans



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Session Beans

In-memory objects that are non-persistent

Designed to perform the processes of a

business

Not survive container crashes

Two types:

Stateless

Stateful


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Stateful Session Bean

Holds conversational state

Stores information for a relatively short

amount of time

Capable of multiple interactions with the

client

Example: on-line shopping cart


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Stateless Session Bean

Doesnt maintain conversational state

Immediately processes the information

received from the client

Example: check out


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Transaction Management

Container-managed transaction demarcation

Beanmanaged transaction demarcation


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Session Bean Elements

Remote Interface

Declares publicly available methods of EJB

Home Interface

Declare create method

Bean implementation class

Implement EJB business methods declared in remoteinterface

implementations for methods declared in homeinterface.

Deployment descriptor

Helper classes (optional)


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Remote Interface

import javax.ejb.EJBObject;

import java.rmi.RemoteException;

public interface CourseRegistration extends EJBObject {//Students add or drop courses

public boolean studentAddSection(int pinNo, int sectionID,boolean isAudit)

throws RemoteException;

public boolean studentDropSection(int pinNo, intsectionID)throws RemoteException;

}


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Home Interface

import java.io.Serializable;


import javax.ejb.CreateException;

import javax.ejb.EJBHome;import java.lang.*;

public interface CourseRegistrationHome extends EJBHome {

CourseRegistration create() throws RemoteException,CreateException;

}


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Bean implementation class(I)import java.rmi.RemoteException;

import javax.ejb.*;

import java.sql.*;

import javax.sql.*;

import java.util.*;

import javax.naming.*;

import javax.naming.Context;

import javax.naming.InitialContext;

import javax.rmi.PortableRemoteObject;

public class CourseRegistrationBean implements SessionBean{

private Connection con;

private String dbName = "java:comp/env/jdbc/AcxiomProDB";

private SessionContext context;

private Person person;

private TermHome tHome;

private Course course;


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Bean implementation class(II)

public boolean studentAddSection(int pinNo, intsectionID, boolean isAudit)throws RemoteException{

return person.addCourse(pinNo, sectionID, isAudit);

}

public boolean studentDropSection(int pinNo, int

sectionID)throws RemoteException{return person.deleteCourseRegistered(pinNo,sectionID);

}


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Bean implementation class(III)public void ejbCreate()throws RemoteException{

try{

Context initial = new InitialContext();

Object objref = initial.lookup("java:comp/env/ejb/SimplePerson");

PersonHome pHome = (PersonHome)PortableRemoteObject.narrow(objref,

PersonHome.class );

person = pHome.create();objref = initial.lookup( "java:comp/env/ejb/SimpleCourse");

CourseHome cHome = (CourseHome)PortableRemoteObject.narrow(objref,

CourseHome.class );

course = cHome.create();

objref = initial.lookup( "java:comp/env/ejb/SimpleTerm");

tHome = (TermHome)PortableRemoteObject.narrow(objref, TermHome.class );

}

catch(Exception ex){

throw new EJBException("ejbCreate: " + ex.getMessage());

}

}


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Bean implementation class(IV)

public CourseRegistrationBean() {}

public void ejbRemove() {}

public void ejbActivate() {}

public void ejbPassivate() {}

public void setSessionContext(SessionContext sc) {}


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Entity Beans

Represent business objects and an in-memory view

of persistent data

Are used to represent data stored in a database Allow shared access from multiple EJB clients

Survive server crashes

Two types of persistence Container-managed

Bean-managed


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Entity Bean Elements Remote Interface

Declares publicly available methods of EJB

Home Interface

Declare

create method

finder method Bean implementation class

Implement EJB business methods declared in remoteinterface

implementations for create and finder methods declaredin home interface.

Deployment descriptor

Helper classes (optional)

Primary key classes(optional)


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Remote Interface

import javax.ejb.EJBObject;


public interface Term extends EJBObject {

public Integer getTermID()throws RemoteException;

public String getTermName()throws RemoteException;

public Integer getTermYear()throws RemoteException;

}


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Home Interface


import javax.ejb.*;

public interface TermHome extends EJBHome {public Term create(String termName, Integer termYear) throws

RemoteException, CreateException;

public Term findByPrimaryKey(Integer termID) throws

FinderException, RemoteException;public Term findByNameYear(String termName, Integer

termYear) throws FinderException, RemoteException;

}


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Bean Implementation Class (I)import java.sql.*;

import javax.sql.*;

import javax.ejb.*;

import javax.naming.*;

public class TermBean implements EntityBean

{

private Integer termID;

private String termName;

private Integer termYear;private EntityContext context;

private Connection con;

private String dbName = "java:comp/env/jdbc/TermDB";


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Bean Implementation Class (II)

public Integer getTermYear()

{

return termYear;

}

public String getTermName()

{

return termName;

}

public Integer getTermID()

{

return termID;

}


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Bean Implementation Class (III)

public Integer ejbCreate(String tName, Integer tYear)throws

CreateException {

Integer id = null;

tName = tName.toUpperCase();

try {

}

catch (Exception ex) {

throw new EJBException("ejbCreate: " + ex.getMessage());

}

}


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Bean Implementation Class (IV)

public void ejbPostCreate(String tName, Integer

tYear)

{ }


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Bean Implementation Class (V)

public void ejbRemove() {

try {

deleteRow(termID);

} catch (Exception ex) {

throw new EJBException("ejbRemove: " +

ex.getMessage());

}

}


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Bean Implementation Class (VI)public void ejbLoad() {

try {loadRow();

} catch (Exception ex) {

throw new EJBException("ejbLoad: " + ex.getMessage());

}

}

public void ejbStore() {

try {

storeRow();

}

catch (Exception ex) {

throw new EJBException("ejbStore: " + ex.getMessage());

}

}


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Bean Implementation Class (VII)

public Integer ejbFindByPrimaryKey(Integer primaryKey) throws Exception

{

boolean result;

try

{

result = selectByPrimaryKey(primaryKey);

}

catch (Exception ex){

throw new Exception("ejbFindByPrimaryKey: " + ex.getMessage());

}

}


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Act as asynchronous message consumers

Use Java Message Service (JMS)

Execute business logic of JMS message

routed by container

Handle only one client at time


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Types of Enterprise JavaBeans

Enterprise JavaBeans(EJB)

Session Bean(SB) Entity Bean(EB) Message Driven Bean(MDB)

Stateless(SLSB)

Stateful(SFSB)

Bean ManagedPersistence

Container ManagedPersistence

Synchronous Communication Asynchronous Communication


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Part III

J2EE Deploytool Demonstration

Tutorial EJB

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