ILP J2EE Stream J2EE 05 Ejb v0.3

8/14/2019 ILP J2EE Stream J2EE 05 Ejb v0.3

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September 3, 2009

J2EEEnterprise Java Beans

Version 1.0


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2September 3, 2009TCS Internal

EJB Defined

The Enterprise JavaBeans architecture is a

component architecture for the developmentand deployment of object-orienteddistributed enterprise-level applications.Applications written using the Enterprise

JavaBeans architecture is scalable,transactional and multi-user secure. Theseapplications may be written once, and

deployed on any server platform thatsupports the Enterprise JavaBeansspecification

Sun Microsystems Enterprise JavaBeans

Specification, v1.1, Copyright 1999 by Sun


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Enterprise Java Beans

Enterprise Java Beans are components which

are deployed within a container.EJB component is a set of classes andinterfaces.

The advantage of components over objectsis that only the business logic has to beaddressed and underlying middlewareservices are taken care by containers.

Containers are executables within serverenvironment which hold the beans.


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EJB AdvantagesProvides a mechanism to store and retrieve

data in a persistent way.It is not necessary that all beans shouldreside in the same machine. Beans fromdifferent machine can talk to each other.

The problem of transaction management isautomatically taken care.

The data transfer between beans is secureeven though it is through network.

Beans run in multithreaded environment.User need not worry about concurrencyproblems.


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EJB ComponentsHome Interface

Extends javax.ejb.EJBHomeProvides remote access to create, find and

remove beans.

Remote Interface

Extends javax.ejb.EJBObject

Provides remote access to businessmethods.

Bean Class

Extends javax.ejb.EnterpriseBean type

Implements business logic and other

functionality.


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EJB Architecture

Implements

Invokes

Creates / uses

Client

Server

Home Interface

EJB Object

(Wrapper)

Enterprise

Java Bean

(Biz Logic)

Remote

Interface

Container

RMI

RMI

Naming Service

You write this


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Types of Enterprise Beans

Session Bean

Performs task for a client

Entity Bean

Represents business entity that exist in a

persistent storageMessage-Driven Bean

To process messages asynchronously

Act like a listener for JMS API.


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Session Bean

Session means various activities done by

the user during one visit to the application. Represents a single client inside the J2EE

server.

To access an application deployed inserver, client invokes session beansmethods.

Session beans shields the client from

complexity of the application.

Session beans are classified into twotypes:

Stateless Session Bean


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Stateless Session Beans

Does not maintain state across various

invocations..Instance variables have state but only forone invocation.

Can handle multiple clients and henceprovide better scalability for large clients.

Better performance than stateful beans.


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Example: SalaryBean

Home Interface:package simpleBean;

public interface SalaryHome extends

javax.ejb.EJBHome {

Salary create() throws java.rmi.RemoteException,

javax.ejb.CreateException;

}

Life

Cycle

Method


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Example: SalaryBean

Remote Interface:package simpleBean;

public interface Salary extends

javax.ejb.EJBObject {

double caculateSalary(int annualSalary,

double bonus)throwsjava.rmi.RemoteException;

}

Business

LogicMethod


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Example: SalaryBean

Salary EJB:package simpleBean;import javax.ejb.*;public class SalaryEJB implements

SessionBean {double caculateSalary(int annualSalary,

double bonus)throwsjava.rmi.RemoteException {double monthly = annualSalary / 12;monthly = monthly + bonus;return monthly;

}public void ejbCreate(){}

public void ejbRemove(){}public void ejbActivate(){}public void ejbPassivate(){}public void setSessionContext(SessionContext ctx){}

}

BusinessLogic

Method

Life

Cycle

Methods


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Example: SalaryBean

Deployment Descriptor:

Single stateless bean to calculate salary

Salary Bean


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Example: SalaryBean

Deployment Descriptor (Continued):Simple bean to calculate salary

Salary BeanSalarysimpleBean.SalaryHomesimpleBean.SalarysimpleBean.SalaryEJBSatelessContainer


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Example: SalaryBean

Directory Structure:simpleBean

|---- Salary.class

|---- SalaryHome.class

|---- SalaryEJB.class

META-INF

|---- ejb-jar.xml

Keeping the files as shown in the directory structure, andusing deploytool, or any other tool,

the SimpleBean.jar can be created.


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Life Cycle of the Stateless Bean

Instance createdusing no-args constructor

setSessionContext

Method called

ejbRemove

called

ejbCreate

Method called

Component

Added to the pool

Container

Needsa new session

bean

Many clients

Use

The bean


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Life cycle of Stateless SessionBean

Does Not Exist

Ready

1.setSessionContext

2.ejbCreate

ejbRemove


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When to use stateless sessionbeans?No data for a specific client

Single method invocation for performing ageneric task of all clients

Fetching and setting often used read-only

data from the database


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Stateful Session Bean

Instance variables represent the state of the

unique client-bean session.The state is retained for the duration of asession.


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Life Cycle of the Stateful Bean

Instance createdusing no-args constructor

setSessionContext

Method called

ejbCreate

Method called

Component

Is ready

Bean does

Not existClient calls

Create()

One client

Use

The bean

Container calls

ejbPassivate

ContainerCalls

ejbRemove

Container calls

ejbPassivate

Client calls

ejbRemove

Timeout


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Life cycle of Stateful Session Bean

Does Not Exist

Ready Passive

1.create

2.setSessionContext

3.ejbCreate

1.remove

2.ejbRemove

ejbActivate

ejbPassivate


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Example: SalaryBean

Home Interface and Remote Interface

remains same as stateless bean.Inside the ejbCreate() method initialization isdone.


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SalaryBean (stateful) Salary EJB: (stateful)

package simpleBean;

import javax.ejb.*; public class SalaryEJB implements SessionBean {

String employee;

double caculateSalary(int annualSalary,

double bonus)throws

java.rmi.RemoteException {

double monthly = annualSalary / 12;

monthly = monthly + bonus;

return monthly;

}

public void ejbCreate(String employee){

this.employee = employee;

}

public void ejbRemove(){}

public void ejbActivate(){}

public void ejbPassivate(){} public void setSessionContext(SessionContext ctx){}

}

Wh t t t f l i


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When to use stateful sessionbeans?When the beans state represents

interaction between client and beanBean needs to hold information acrossmethod invocations.

Bean mediates between client and othercomponents in application


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Entity Bean

Entity Bean represents a business object in a

persistent storage mechanism.Each entity bean has an underlying table ina relational database.

Each instance of a bean corresponds to arow in that table.


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Properties of Entity BeanPersistence

States exist beyond the lifetime ofapplication

Shared Access

Can be shared by multiple clients

Built-in transaction management

Primary key

Unique object identifier

RelationshipsBetween multiple entity beans, similar to

relationships in database.


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Types of PersistenceBean-managed Persistence

Bean directly access the databaseDatabase access code is written within

bean.

Container-managed Persistence

Container handles database access

Bean is independent of underlyingpersistence storage mechanism.

No need to modify or recompile the codewhen database is changed.


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Abstract Schema

Abstract schema is part of beans

deployment descriptor.Defines beans persistent fields andrelationships.

Name of the abstract schema is referencedby queries written in Enterprise Java BeansQuery Language.


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Example of Abstract Schema

OrderEJB

LineItemEJB

ProductEJB

CustomerEJB

ONE

MANY

ONE

ONE

MANY

MANY


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Abstract Schema

Persistent Fields

Fields stored in the database

Constitute the state of bean

EJB container automatically synchronizes

with database fields.No instance variables, but only getter and

setter methods.

In container managed persistence thesefields are virtual.


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Abstract Schema

Relationship Fields

Similar to the foreign key in databasetable

These fields are virtual and defined in the

bean class with access methodsDoes not represent the beans state


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Container Managed Relationships

Defines how one

instance of a bean isassociated/relatedwith an instance ofanother bean

One-to-One

One-to-Many

Many-to-One

Many-to-Many

Example: Container Managed


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Example: Container ManagedBean(CMB) Home Interface:package cmp;

import java.util.Collection;import java.rmi.RemoteException;import javax.ejb;public interface TaxHome extends EJBHome {

public Tax create(String stateCode,String taxRate)throws

RemoteException, CreateException;public Tax findByPrimaryKey(String primaryKey)throws FinderException, RemoteException;

}Note:14. Unlike session beans, create method has parameters passed to it.

These represents beans state and mapped to two columns in Tax

table.15. finderMethods are used to find a record from the table.



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Example: Container ManagedBean(CMB) Remote Interface (Component Interface):

package cmp;import javax.ejb;

public interface Tax extends EJBObject {

public void setTaxRate(float taxRate)throws

RemoteException;

public float getTaxRate()throws RemoteException;

}

Note:

10. Defines two business methods.



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Example: Container ManagedBean(CMB) Entity Bean Class:

package cmp;import javax.ejb;

public interface TaxEJB implements EntityBean {

public String stateCode;

public float taxRate;

public void setTaxRate(float taxRate)throws

RemoteException{this.taxRate = taxRate;

}

public float getTaxRate()throws RemoteException{

return this.taxRate;

}



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Example: Container ManagedBean(CMB) Entity Bean Class (Continued):

public String ejbCreate(String stateCode,String taxRate)

throws CreateException {

if(stateCode == null){

throw new CreateException();

}

this.stateCode = stateCode;this.taxRate = taxRate;

return null;

}

Note:

13. This method is invoked on behalf of create method defined inhome interface.

Example: Container Managed Bean


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Example: Container Managed Bean(CMB) Entity Bean Class (Continued):

public void ejbLoad();public void ejbStore();

public void ejbRemove();

public void unsetEntityContext();

public void setEntityContext(EntityContext cxt){}

public void ejbActivate(){}

public void ejbPassivate(){}

Note:

10. Life cycle methods



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Example: Container Managed Bean(CMB)


Persistant tax calculator

TaxCMB



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Example: Container Managed Bean(CMB) Deployment Descriptor (continued):

Tax calculation business model.

TaxBean

TaxBeancmp.TaxHome

cmp.Tax

cmp.TaxEJB

Container

Container



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Example: Container Managed Bean(CMB)

Deployment Descriptor (continued):java.lang.Stringfalse

Tax rate

taxRate

State Code

stateCode

stateCode


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Example: Container Managed Bean (CMB)

Deployment Descriptor (continued):

TaxBean

*

Not Supported

Bean Managed Persistence Beans(


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Bean Managed Persistence Beans(BMP)BMP beans are similar to CMP beans.

The only difference is that we have to writethe JDBC code to talk to the database. (In theearlier case we didnt do that).

In the deployment descriptor is modifiedaccordingly.



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Example: Container Managed Bean(BMB)


Persistant tax calculator

TaxCMB



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Tax calculation business model.

TaxBeanTaxBean

cmp.TaxHome

cmp.Tax

cmp.TaxEJB

Container

Container


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Example: Container Managed Bean (BMB)

Deployment Descriptor (continued): java.lang.String

false

JDBC/CloudSpace

javax.sql.DataSource

Container



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TaxBean

*

Not Supported


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When to use Entity Beans?

When the bean represents entity and not

procedureCreditCardEJB is an entity bean, while

CriditCardValidateEJB is a session bean.

When the beans state must be persistent.


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Life cycle of Entity Bean

Does Not Exist

Ready Pooled

setEntityContextunsetEntityContext

ejbActivate

ejbPassivate

1.create

2.ejbCreate

3.ejbPostCreate

1. remove

2.ejbRemove


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d i


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Message driven BeanClients do not access these beans through

interfaces.Instances of message driven bean retain nodata / state.

All instances are equivalent, allowing

container to assign an message to anymessage-driven bean instance.

A single bean can process messages frommultiple clients.

When to use Message Driven


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When to use Message DrivenBeans?Synchronous message transfer by session

and entity beans blocks system resources.To avoid this, message-driven beans can beused.

Lif l f M B


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Life cycle of Message Bean

Does Not Exist

Ready

1.setMessageDrivenContext

2.ejbCreate

ejbRemove

onMessage

R f


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Reference

Stephanie Bodoff, et. al., The J2EE Tutorial,

Sun Microsystems.James Mc Govern, et. al., J2EE 1.4. Bible

S Allamaraju., et. al., Professional Java

Server Programming. (J2EE 1.3 Ed).Rahim Adatia, et. al., Professional EJB

Documents

ILP J2EE Stream J2EE 05 Ejb v0.3