session 3 tp3

ACCP2005/EJB 2.0/Session 3/1 of 31

Stateless Session Beans

Session 3


Session Objectives

Identify the constituents of an Enterprise JavaBean.

Define a bean class, EJB object, home interface, home object and deployment descriptors.

Define a stateless session bean Write programs related to stateless session

beans Compile and deploy stateless session beans


Review of Session 2-(1of 2)In session 2 we discussed Four stages are followed while developing

business solutions Six parties are involved while deploying

Enterprise JavaBeans Logical three-tier architecture of EJB:

The Client The EJB Server The Database

The EJB Container resides inside the EJB server. The container acts as a buffer between the bean and the outside world.

The responsibility of the EJB Server and Container


Review of Session 2-(2 of 2) The server and the container provide following

services to the developer * Transaction support * Security support * Persistence support * Support for management of multiple instances . An Enterprise Java Bean can be classified into:

* Session Beans

* Entity Beans * Message-Driven Beans


Components of an Enterprise Bean

Components of an enterprise bean

The bean class

The EJB object

The Remote interface

DeploymentDescriptors

The Home Interface

The EJB-jar file

The Home object

The Local InterfaceThe LocalHome

Interface


The Bean class

Well-defined interfaceThe Bean Bound

Communicates to the client through the

interface

Container

Works in any container with the

help of these interfaces

public interface javax. ejb. EnterpriseBean extends java.io.Serializable {}

Once the above interface is implemented, the bean class is confirmed


The EJB Object

Client Code

EJB Container/Server

1 .Calls a method

4.Returns method to client

Home Object

EJB Object

3. Returns the Method

Enterprise Bean

Instance

2. Delegates method to bean

The container is the middleman between the client and the bean. It manifests itself

as a single network-aware object.

This network-aware object is called the EJB Object


The Remote Interface

Remote Interfaces derived from javax.ejb.EJBObject

Business Methods

Define

Perform

Functionality of the bean

javax.ejb.EJBObject

public interface java.rmi.RemoteInterfaceextends javax.ejb.EJBObject{

public abstract javax.ejb.EJBHome getEJBHome() throws java.rmi.RemoteException;}


Relationship between Java RMI and EJB Objects

Bean

Java Virtual Machine

Bean

Java Virtual Machine

Location Transparency

Remote Method Invocation

Portability of Client Code

EJB Object java.rmi.Remote Remote Object

JVM

JVM


Methods under javax.ejb.EJBObject

javax.ejb.EJBObject

getEJBHome()

getPrimaryKey()

remove()

getHandle()

isIdentical()


The Home InterfaceHome

Interface

Find EJB Objects Create EJB

Objects

Destroy EJBObjects

EJB specifies certain methods that the home interface has to support. These methods are defined in the javax.ejb.EJBHome

public interface javax.ejb.EJBHome extends java.rmi.Remote {

public abstract EJBMetaData getEJBMetaData()throws java.rmi.RemoteException;

}


The Methods in EJB Home

getEJBMetaData(): It is this method that gets information about the beans that are being worked on

remove(): This method destroys an EJB object

The methods that fall under the EJB Home are


The Home Object

Client Code

Home Object

EJB Object

Enterprise Beans


1. Requests new EJB Object

3. Returns the objects

2. Creates new object


Deployment Descriptors

Deployment Descriptors

Life cycle requirements and Bean management

Persistence RequirementsTransaction Requirements

Security Management

Classes that form the bean

Home Interface

Remote Interface

EJB Server


Life Cycle of a Session Bean

A session bean may last as long as the client session.

Will not survive if the application server changes or crashes.

They are objects which are present in-memory which die along with the surrounding environment and are not persisted in a database.


Conversational and Non Conversational Beans

A conversation stretches across a business process with respect to the client.

A stateless session bean conducts a conversation that spreads over a single method call.

Stateful session beans can retain their conversational state.

Client Conversation Bean


Writing a Session BeanThe six methods to be followed while

writing a session bean

setSessionContext(SessionContext ctx)

ejbCreate()

ejbPassivate()

Business methods

ejbRemove()

ejbActivate()


The setSessionContext (SessionContext ctx)

Container

setSessionContext() Bean

public class theBean implements SessionBean{

private SessionContext ctx;public void setSessionContext(SessionContext ctx){

this.ctx=ctx;}. . . . . . .

}

Session Context(Gateway)

Associates


Business Methods

import javax.ejb.*;public class sess implements Sessionbean{

public int multiply(int a, int b){return (a*b); }

ejbPassivate() ejbCreate() ejbActivate() ejbRemove() . . . . . . . }

Business methods are written to solve business logic problems. Business methods are contained in the remote interface of the bean for the client to access them.


Using JNDI to lookup Home Objects

Home Object

Enterprise beans

EJB Object

Client

JNDI

Naming Service

1. Retrieve Home Object

3. Creates an EJB Object

5. Return Object reference

6. Invokes business methods


4. Create EJB Object

2. Returns reference to the home object

7. Delegates request to bean


Steps in accessing Home Objects

The steps followed by the client code to get a reference

The setting up of the Environment

Destroying the EJB Object

Calling a Method

Creating an Object

Retrieving the home objects

The Initial Context


Pooling of Stateless Session Bean

Client

EJB Object

Invokes

EJB Server/Container

Bean

Bean

Bean

Bean Invokes


Deployment Descriptors specifies how the container is supposed to

create and manage the enterprise bean object. defines the name of the enterprise bean class,

and the names of the home and remote interfaces.

ejb-jar file provides naming information about enterprise bean, remote interface and home interface.

ejb.jar has to be present in the directory called META-INF.


jboss.xml Provides the container information

about the JNDI mapping, persistence information and database mapping.

This file also has to be put into the META-INF file.

<jboss> <enterprise-beans>

<session> <ejb-name>Welcome</ejb-name> <jndi-name>Welcome</jndi-name>

</session> </enterprise-beans></jboss>


Creating the jar file

Welcome.classDeployment Descriptors

Welcome.jar

Welcomebean.classWelcomehome.class

A jar file is created to package the three java files, namely the bean class, the home interface and the remote interface. The XML files Namely ejb-jar.xml and jboss.xml are also present in the jar file.


Deploying the bean the newly created .jar file has to be

copied into the deploy directory on the server. D:\bin\jboss\deploy

.jar file.jar file

jar cvf welcome.jar Welcome.class Welcomehome.class Welcomebean.class META-INF


Accessing from Client sidePossible Clients

Ordinary JavaBean

Enterprise JavaBean

JSP Page

Servlet

Applet

Enterprise JavaBean

HomeObject

EJB Object

JNDI lookup

create()

Business Methods


Summary - 1 The bean class, the EJB object, the remote interface, the home

interface, the home object, the deployment descriptors, and the jar files constitute the enterprise bean.

The bean class contains the implementation of the business logic methods.

The EJB container performs certain important management functions when it intercepts client requests. These management functions are:

* Transaction logic* Security logic* Bean instance logic

The Remote interface duplicates the methods exposed by the bean class.


Summary - 2 Responsibilities of the EJB home object:

* Creating EJB objects* Searching for existing EJB Objects* Removing EJB Objects

The deployment descriptor: A file that tells the EJB server about the classes, the home interface, and the remote interface that form the bean.

The lifetime of a session bean may last till such time as that of a client session. It could be as long as a window is open or as long as an application is open. Session beans do not, therefore, survive application server crashes or machine

crashes.


Summary - 3 Three classes are essential for deployment:

* Home Interface* Remote Interface* Bean class

The ejb-jar.xml file is a compressed file that contains the declarations of the enterprise bean class, the remote interface and the home interface.

It is important to have a client because EJB will not function without the client. This client can be:

* An ordinary JavaBean* Another EJB* A JSP Page* A servlet* An applet*A stand-alone application