Bài giảng lập trình mạng stateless session bean GV nguyễn xuân vinh

Components of an Enterprise BeanComponents of an enterprise bean The bean class The EJB object The Remote interface Deployment Descriptors The Home The EJB-jar file The Home object The

EJB: Stateless Session Bean

Presenter: Nguyễn Xuân Vinh Information Technology Faculty

home object and deployment descriptors.

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:

* 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

Deployment Descriptors

The Home

The EJB-jar file

The Home object

The Local Interface The LocalHome

Interface

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

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

Business Methods

Define

Perform

Functionality of the bean

Location Transparency Remote Method Invocation

Portability of Client Code

EJB Object java.rmi.Remote Remote

Object

JVM JVM

Find EJB

Objects

Destroy EJB Objects

EJB specifies certain

methods that the home

interface has to support

These methods are defined

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

EJB Object

Enterprise Beans

EJB Container/Server

1 Requests new EJB Object

3 Returns the objects

2 Creates new object

Life cycle requirements

and Bean management

 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.

The six methods to be followed while writing a session bean

The setSessionContext (SessionContext ctx)

Session Context (Gateway)

Associates

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

3 Creates an EJB Object

5 Return Object reference

6 Invokes business methods

EJB Container/Server

4 Create EJB Object

2 Returns reference

to the home object

7 Delegates request to bean

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

BeanBean

Bean

Invokes

 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

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

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

Deploying the bean

 the newly created jar file has to be copied into

the deploy directory on the server

Home Object

EJB Object

JNDI lookup

create()

Business Methods

 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

 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.

 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: