EJB: the details

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“Basi di Dati Web e Distribuite” – Laurea Specialistica in Informatica – Università di Trento

EJB: the details

Actors:

Component Interface:Same role as in RMI

Component Implementation:Same role as in RMI

Home Interface:Implemented by the server, plays the role of a factory class for the component

JNDI service:Plays the same role as the register in RMI

NamingService

DirectoryMachine

Client

ClientMachine

The logical architecture

App server (container)Machine

HomeInterface

Trovami la Home interface

Dammi unaistanza

Istanza

Crea o recupera una istanza

Metodo()

Session Beans -) stateless -) stateful

Stateful Example

Stateless Example: Euro Converter

Stateful Example – suggested hierarchy

server client

srcsrc

META-INF

ejb-jar.xml

deploy

xHome.javaxHome.class

client.javax.java

xBean.java

x.class

xBean.class xHome.classx.class

Stateless example – The Component (Remote) Interface

package statelessDemo;

import java.rmi.*;import javax.ejb.*;

public interface Converter extends EJBObject { public double convert(int lire);}

Stateless example – The Home Interface

package statelessDemo;import java.rmi.*;import javax.ejb.*;

public interface ConverterHome extends EJBHome { public Converter create() throws RemoteException, CreateException;}

Stateless example – The bean

package statelessDemo;import java.rmi.*;import javax.ejb.*;

public class ConverterBean implements SessionBean { private SessionContext sessionContext; public void ejbCreate() {} public void ejbRemove() {} public void ejbActivate() {} public void ejbPassivate() {} public void setSessionContext(SessionContext sessionContext) { this.sessionContext = sessionContext; } private static double ratio=1936.27; public double convert(int lire) { return lire/ratio; }}

Stateless example – The descriptor

<?xml version="1.0" encoding="UTF-8"?><!DOCTYPE ejb-jar PUBLIC "-//Sun Microsystems, Inc.//DTD Enterprise JavaBeans 1.1//EN" "http://java.sun.com/j2ee/dtds/ejb-jar_1_1.dtd"><ejb-jar> <description>A simple demo of a stateless Bean</description> <display-name>An Euro Converter Bean</display-name> <enterprise-beans> <session> <description>A converter from Lire to Euro</description> <ejb-name>EuroConverter</ejb-name> <home>statelessDemo.ConverterHome</home> <remote>statelessDemo.Converter</remote> <ejb-class>statelessDemo.ConverterBean</ejb-class> <session-type>Stateless</session-type> <transaction-type>Container</transaction-type> </session> </enterprise-beans>

Stateless example – The descriptor

<assembly-descriptor> <container-transaction> <method> <ejb-name>EuroConverter</ejb-name> <method-name>*</method-name> </method> <trans-attribute>Required</trans-attribute> </container-transaction> </assembly-descriptor> <ejb-client-jar /></ejb-jar>

structure of the jar file

META-INF

ejb-jar.xml

statelessDemo

Converter.class

In this directory, run jar cvf converter.jar *

ConverterBean.class ConverterHome.class

this directory(ies) reflect the package hierarchy

Watch out! Packages often make life complex.(it’s easy to make mistakes) Try first without packages.

Compile the sources, generate jar file

clsjavac Converter.javamove Converter.class statelessDemo\javac ConverterHome.javamove ConverterHome.class statelessDemo\javac ConverterBean.javamove ConverterBean.class statelessDemo\

cd ..\deploymentdel *.jardel statelessDemo\*.class

move ..\src\statelessDemo\* statelessDemo\jar cvf Converter.jar *cd ..\src

Start the container

We assume you installed the j2ee sdk distribution provided by

Sun in some %J2EE_HOME% directory.

1) Run %J2EE_HOME%/bin/j2ee.bat2) Run %J2EE_HOME%/bin/deploytool.bat

Start the container

FileNew Application…

FileAdd to Application… EJB-JAR(scegliere converter.jar)

View the properties

Start deployment

ToolsDeploy

Check this box

Crea ConverterApp.ear

Start deployment

Choose a JNDI name

Start deployment

Crea ConverterAppClient.jar

Stateless example – The client

import javax.ejb.*;import javax.naming.InitialContext;

public class ConverterClient { public ConverterClient() { } public static void main(String[] args) { try { InitialContext ctx=new InitialContext(); Object objref=ctx.lookup("L2EConverter");

statelessDemo.ConverterHome home = (statelessDemo.ConverterHome) javax.rmi.PortableRemoteObject.narrow( objref,statelessDemo.ConverterHome.class);

statelessDemo.Converter bean=home.create();

Get naming context and object reference

Cast to correct type

Get a bean instance from container

JNDI name

Stateless example – The client

int lire=100000; System.out.println(lire+" Lire = "+

bean.convert(lire)+" Euro"); } catch (javax.naming.NamingException ex) { System.out.println("NamingException: "+ex); } catch (ClassCastException cc) { System.out.println(" ClassCastException : "+cc);} catch (javax.ejb.CreateException ce) { System.out.println("CreateException: "+ce); } catch (java.rmi.RemoteException re) { System.out.println("RemoteException: "+re); } }}

Do your business

Compile the client

clscd client\statelessDemo\copy ..\server\deployment\statelessDemo\Converter.class .copy ..\server\deployment\statelessDemo\ConverterHome.class .cd ..javac ConverterClient.java

Questa è la directory che contiene i sorgenti del client

Stateless example – execution

java -classpath .;%J2EEHOME%\lib\j2ee.jar;…\ConverterAppClient.jar -Dorg.omg.CORBA.ORBInitialHost=localhost ConverterClient

100000 Lire = 51.64568990894865 Euro

Stateful Example

Stateful Example: Dollar Converter

Stateful example – The Component (Remote) Interface

public interface DollarConverter extends EJBObject {

public double convertInEuro(double dollar) throws java.rmi.RemoteException;

public double convertInDollar(double euro) throws java.rmi.RemoteException;

public void setRate(double euro_dollar_ratio) throws java.rmi.RemoteException;

Stateful example – The Home Interface

public interface DollarConverterHome extends EJBHome { public DollarConverter create() throws RemoteException,

CreateException;}

Stateful example – The bean

public class DollarConverterBean implements SessionBean { private SessionContext sessionContext; public void ejbCreate() {} public void ejbRemove() {} public void ejbActivate() {} public void ejbPassivate() {} public void setSessionContext(SessionContext sessionContext) { this.sessionContext = sessionContext; }

Stateful example – The bean

private double euro_dollar_ratio=1;

public double convertInEuro(double dollar) throws java.rmi.RemoteException{

return dollar/euro_dollar_ratio; }

public double convertInDollar(double euro) throws java.rmi.RemoteException{

return euro*euro_dollar_ratio; }

public void setRate(double euro_dollar_ratio) throws java.rmi.RemoteException{

this.euro_dollar_ratio=euro_dollar_ratio; }}

Stateful example – The descriptor

<?xml version="1.0" encoding="UTF-8"?><!DOCTYPE ejb-jar PUBLIC "-//Sun Microsystems, Inc.//DTD Enterprise JavaBeans 1.1//EN" "http://java.sun.com/j2ee/dtds/ejb-jar_1_1.dtd"><ejb-jar> <description>A simple demo of a stateful Bean</description> <display-name>An Euro to Dollar Converter Bean</display-name> <enterprise-beans> <session> <description>A converter from Euro to Dollar</description> <ejb-name>DollarConverter</ejb-name> <home>DollarConverterHome</home> <remote>DollarConverter</remote> <ejb-class>DollarConverterBean</ejb-class> <session-type>Stateful</session-type> <transaction-type>Container</transaction-type> </session> </enterprise-beans>

Stateful example – The descriptor

<assembly-descriptor> <container-transaction> <method> <ejb-name>DollarConverter</ejb-name> <method-name>*</method-name> </method> <trans-attribute>Required</trans-attribute> </container-transaction> </assembly-descriptor> <ejb-client-jar /></ejb-jar>

Stateful example – The client

import javax.ejb.*;import javax.naming.InitialContext;import javax.rmi.PortableRemoteObject;

public class ConverterClient { public ConverterClient() {} public static void main(String[] args) { Object objref=null; DollarConverterHome home=null; DollarConverter bean=null; try { InitialContext ctx=new InitialContext(); objref=ctx.lookup("EDC"); home =(DollarConverterHome)PortableRemoteObject.narrow(

objref,DollarConverterHome.class);

bean=home.create();

Get naming context and object reference

Cast to correct type

Get a bean instance from container

JNDI name

Stateful example – The client

bean.setRate(0.978);

double euro=1000; System.out.println(euro+" Euro = "

+bean.convertInDollar(euro)+" Dollar");

double dollar=1000; System.out.println(dollar+" Dollar = "

+bean.convertInEuro(dollar)+" Euro");

} catch (Exception e) { e.printStackTrace(); } }}

Do your business

Stateful example – execution

java -classpath .;%J2EEHOME%\lib\j2ee.jar;…\DollarConverterAppClient.jar -Dorg.omg.CORBA.ORBInitialHost=localhost ConverterClient

1000.0 Euro = 978.0 Dollar1000.0 Dollar = 1022.4948875255624 Euro

Session Beans Lifecycle: client’s view

Does not existIs not referenced

ExistsIs not referenced

ExistsIs referenced

Does not existIs referenced

home.create()

Clientreleasesreference

Crash,Timeout

Clientreleasesreference

Clientobtainshandle

object.remove(),home.remove(),Crash, timeout

Clientinvokesmethod

Client invokes method (NoSuchObject Exception)

Stateless session Beans Lifecycle

ExistsIn the pool

Does not exist

ejbRemoved()

Client invokes method

Client invokes method (NoSuchObject Exception)

1) newInstance()2) setSessionContext(sc)3) ejbCreate()

Client invokes create()Container executes: Client invokes remove()

Container executes:

Stateful session Beans Lifecycle

Passive

ejbPassivate()

ejbActivate()

Exists, method ready

in the pool

Does not existClient invokes remove(), or timeout is reachedContainer executes:ejbRemoved()

Client invokes create()Container executes:1) newInstance()2) setSessionContext(sc)3) ejbCreate()

Client invokes non TX method

Exists, method ready

Client invokes TX method

Client invokes TX methodAfterBegin()

Client invokes commitbeforeCompletion()afterCompletion(true)

Client invokes rollbackafterCompletion(false)

EJB: the details

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