EJB: the details

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

EJB: the details

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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

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NamingService

DirectoryMachine

Client

ClientMachine

The logical architecture

Pool

App server (container)Machine

HomeInterface

Trovami la Home interface

Dammi unaistanza

Istanza

Crea o recupera una istanza

Trova

Metodo()

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Session Beans -) stateless -) stateful

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Stateful Example

Stateless Example: Euro Converter

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Stateful Example – suggested hierarchy

App

server client

srcsrc

META-INF

ejb-jar.xml

deploy

xHome.javaxHome.class

client.javax.java

xBean.java

x.class

xBean.class xHome.classx.class

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Stateless example – The Component (Remote) Interface

package statelessDemo;

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

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

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Stateless example – The Home Interface

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

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

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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; }}

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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>

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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>

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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.

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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

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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

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Start the container

FileNew Application…

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

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View the properties

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Start deployment

ToolsDeploy

Check this box

Crea ConverterApp.ear

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Start deployment

Choose a JNDI name

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Start deployment

Crea ConverterAppClient.jar

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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

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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

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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

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Stateless example – execution

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

100000 Lire = 51.64568990894865 Euro

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Stateful Example

Stateful Example: Dollar Converter

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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;

}

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Stateful example – The Home Interface


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

CreateException;}

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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; }

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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; }}

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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>

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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>

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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

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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

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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

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Session Beans Lifecycle: client’s view

Does not existIs not referenced

ExistsIs not referenced

ExistsIs referenced

Does not existIs referenced

Start

home.create()

Clientreleasesreference

Crash,Timeout

Clientreleasesreference

Clientobtainshandle

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

Clientinvokesmethod

Client invokes method (NoSuchObject Exception)

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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:

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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

in TX

Client invokes TX method

Client invokes TX methodAfterBegin()

Client invokes commitbeforeCompletion()afterCompletion(true)

Client invokes rollbackafterCompletion(false)

Date post:	21-Jan-2016
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EJB: the details

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