A Practical Approach to EnterPrise Java Beans_site

8/2/2019 A Practical Approach to EnterPrise Java Beans_site

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Kantimahanti Prasad

BY

The Heart of J2EE

EJB

[email protected] or [email protected]

Copyright 2004 Kanti Prasad All rights reserved

IN 30 MINs

A Component Technology

A Practical Introduction to

Enterprise Java BeansDO YOU WANT

TO ANSWER MOSTOF THE

EJB QUESTIONS ?

THEN LET MEHELP YOU!
mailto:[email protected]:[email protected]:[email protected]:[email protected]


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A STAR or adifferent color

represents

importantpoints to NOTE

1. Learning objectives

1. Component Technology characteristics

2. Standard Infrastructure needs

3. Application Servers

4. Containers

5. J2EE Architecture and its components6. EJB Model, Overview & JNDI

7. EJB Specifications, Roles

8. EJB Design Approaches, Architecture

9. Types of Beans

10. EJB Interfaces & Session Contexts11. Life cycles of different Beans

12. EJB Jar files & Deployment Descriptor

13. Sample examples

14. Components comparison



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2. About the AuthorKantimahanti.N.S.Prasad

Worked in fortune 100 Corporates in Client Server Technologies.

Specializes inArchitecture, Designing, Development & Managing day-to-day activities.

Presently doing a PhD at Queens Uty, U.K in Adaptable Software specific toComponent Technologies and has a M.B.A(Computer Applications) from an U.S. Uty.

Business domain strengths are in Investment banking & Insurance.

Process improvement strengths are in 6 - Sigma and CMM.

His present & past working experiences in various global locations are in corporates likePramerica (Prudential U.S), J P Morgan Chase, A B N Amro Bank & SGS.

He was a part time visiting faculty in affiliates of Sydney University, Australia and All India ManagementInstitute teaching I.T, Project Management & Statistics. He has given some presentations on ProjectManagement and TQM at various venues. He has won few Talent/STAR performance awards and playsalmost all the sports what are under the Sun.

He hails from Vizag/ Hyderabad India. His 3rd party tested Temperament Sorter results are belowhttps://www.advisorteam.com/temperament_sorter/testresult.asp?TID=740281673499&PID=15800https://www.advisorteam.com/temperament_sorter/testresultc.asp?TID=740281662156&PID=13606

If you liked his presentation, tell others and if you have a comment, tell him. He can be reached [email protected] or [email protected]

U NEVER

FAIL

TILL U QUIT
https://www.advisorteam.com/temperament_sorter/testresult.asp?TID=740281673499&PID=15800https://www.advisorteam.com/temperament_sorter/testresultc.asp?TID=740281662156&PID=13606mailto:[email protected]:[email protected]:[email protected]:[email protected]://www.advisorteam.com/temperament_sorter/testresultc.asp?TID=740281662156&PID=13606https://www.advisorteam.com/temperament_sorter/testresultc.asp?TID=740281662156&PID=13606https://www.advisorteam.com/temperament_sorter/testresultc.asp?TID=740281662156&PID=13606https://www.advisorteam.com/temperament_sorter/testresultc.asp?TID=740281662156&PID=13606https://www.advisorteam.com/temperament_sorter/testresultc.asp?TID=740281662156&PID=13606https://www.advisorteam.com/temperament_sorter/testresultc.asp?TID=740281662156&PID=13606https://www.advisorteam.com/temperament_sorter/testresultc.asp?TID=740281662156&PID=13606https://www.advisorteam.com/temperament_sorter/testresultc.asp?TID=740281662156&PID=13606https://www.advisorteam.com/temperament_sorter/testresultc.asp?TID=740281662156&PID=13606https://www.advisorteam.com/temperament_sorter/testresultc.asp?TID=740281662156&PID=13606https://www.advisorteam.com/temperament_sorter/testresultc.asp?TID=740281662156&PID=13606https://www.advisorteam.com/temperament_sorter/testresultc.asp?TID=740281662156&PID=13606https://www.advisorteam.com/temperament_sorter/testresult.asp?TID=740281673499&PID=15800https://www.advisorteam.com/temperament_sorter/testresult.asp?TID=740281673499&PID=15800https://www.advisorteam.com/temperament_sorter/testresult.asp?TID=740281673499&PID=15800https://www.advisorteam.com/temperament_sorter/testresult.asp?TID=740281673499&PID=15800https://www.advisorteam.com/temperament_sorter/testresult.asp?TID=740281673499&PID=15800https://www.advisorteam.com/temperament_sorter/testresult.asp?TID=740281673499&PID=15800https://www.advisorteam.com/temperament_sorter/testresult.asp?TID=740281673499&PID=15800https://www.advisorteam.com/temperament_sorter/testresult.asp?TID=740281673499&PID=15800https://www.advisorteam.com/temperament_sorter/testresult.asp?TID=740281673499&PID=15800https://www.advisorteam.com/temperament_sorter/testresult.asp?TID=740281673499&PID=15800https://www.advisorteam.com/temperament_sorter/testresult.asp?TID=740281673499&PID=15800https://www.advisorteam.com/temperament_sorter/testresult.asp?TID=740281673499&PID=15800


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3. Thank you note

He wishes to thank Paul Perrone , Paulo Merson & Ramesh Behra for making

this tutorial look the way it does.

He wishes to thank Joerg Mueller, Muruganandam, CharlesJohnson & VenuGadium who had volunteered to do the editing of this presentation.

his Sisters

Thank you for downloading my Presentation

Special thanks to all his Managers at Pramerica and Prudential U.S.

& his Cousinshis BrothersDr.Rao &Family

his ParentsSADHGISUNAYANA

ARUNA

DEDICATED TOCopyright 2004 Kanti Prasad All rights reserved

He wishes to thank to Katherine Ballantyne, Choi Kwan who volunteers toedit all of his Articles & Presentations.


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4. Component Technology

Components are deployable units that provide a

business service to their clients.

Each component provides an interface in the form of operations,properties and events

Components can be developed in any language such as JAVA,C++,VB

Components are frequently organized into application frameworks for

vertical domains Component models such as Active X and EJB standardize

communication and allow for prebuilt purchased components



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5. Component Characteristics

Properties Reusability

Operations Shareable

Events Distributable

Deployable Self Containment

Self description

Components Characteristics include



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Components should have a mechanism for exporting

6. Component P O E

Properties

Operations

Events



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7. Deployable Components

Components are operation independent of

Hardware

The underlying operating system

Their Application Server

The network protocol they use



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8. Reusable Components

Component services can be used as a part of

business logic of other components



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9. Shareable Components

If multiple clients are using a component

simultaneously, the component will provide

the same quality of service to all the clients



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10. Distributable Components

Components should provide services to clients

running locally or remotely

RemoteCLIENTS

EJB Container

EJB

Possible

RemoteCLIENTS

RemoteCLIENTS

RemoteCLIENTS

LocalCLIENTS



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11. SelfContained Components

Components should only contain the code

necessary to implement their services

Infrastructure services should be injected by

the execution environment



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12. Standard Infrastructure Needs

Standard infrastructure services include

Directory Services Distributed transaction management

Security management

Concurrent access management

Persistence management

Resource pooling (e.g. DB connections) Administration interface

Load Balancing

Fault tolerance



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13. Applicatoin Servers

An application server provides the infrastructure and

services to run components/applications

J2EE

basedsolutions

Non-J2EEsolutions

(PHP, Cold Fusion,Perl, etc.)

Microsoft Solutions

(COM, ASP.NetVB.Net,C# etc.)

Application Server products are mostly



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14. Object Pooling

An application server may create a pool of bare objects

that may be used as EJBs when requests are made

App Server

EJB Container

CLIENT

NetworkDB

CLIENTEJB

EJB

EJB

EJB

EJB

EJB

Pool



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15. Directory of Application Servers

Application Servers provide clients access to software orother applications that run only on the server

Examples include web servers, e-mail servers and database servers

Popular Application Servers are:

I.B.M. Web Sphere

BEA Web Logic

Sun Java System Application Server 7.x

Jboss

The full list with vital statistics are available at

http://www.devx.com/enterprise/html/16268

http://www.javacommerce.com/articles/serverlist.htm

http://www.devx.com/enterprise/html/16268http://www.javacommerce.com/articles/serverlist.htmhttp://www.javacommerce.com/articles/serverlist.htmhttp://www.devx.com/enterprise/html/16268


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Container provides System services like

App Server

CLIENT

NetworkSTUB

Persistence Security Connection Pooling ThreadingTransaction

EJB Container

EJB

Fish cannot survive outside water &EJBs cannot survive outside containers

Containerinterceptsrequests


Container knows what to do, as you describe everything in a special descriptor file

A Container : provides the environment in which a bean executes

generates Home Object

generates EJB Object

manages individual bean instances

EJB

EJB

&

Container means a

pre developed Software

To increase capability.

clustering is taken care

by the vendor

Implicit Middleware

gained through declaration

16. Container


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17. J2EE Overview

Hardware Platform

Operating System Platform

J2EEContainer/Server

Operating SystemIndependence

Hardware Independence

Common ProgrammingServices

Distributed Communication

Services

J2SE RuntimeJ2SE Language/Interfaces

services standards component-based

Enterprise Components

Application ServerIndependence

Database Independence

Web Server Independence

Enterprise ResourceManagement Services

Deployment/Configuration

Management ServicesJ2EE Interfaces

Data

DeploymentDescriptors (DDs)

DeployTools



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J2SE

Application ClientContainer

DBSAAJ

JAX-RPC

CONJMX

JMS

WEBS

JAXR

JDBC

MgmtDAO

Client

J2SE

SAAJ

JAX-

RPC JTA

CONJMX

Mgmt

JAF

Java

MailJMS

J

ACC

W

EBS

J

AXR

J

NDI

J

DBC

AppletContainer

J2SE

HTTP/S

HTTP/S

Web Container

JSP ServletApplet

2 TIER

3 TIER

SAAJ

JAX-

RPC JTA

CONJMX

Mgmt

JAF

Java

MailJMS

J

ACC

W

EBS

J

AXR

J

NDI

J

DBC

EJB Container

J2SE

RMI/IIOP

RMI/IIOP

4 TIER

EIS

MainFrames

EJB

J2EE defines a model for developing multi-tier, web based,

enterprise applications with distributed components

18. J2EE 1.4 APIs

For all the APIs refer http://java.sun.com/j2ee/1.4/docs/tutorial/doc/index.html

JSP Servlet ENGINE



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19. Enterprise JavaBeans Model

EJB is Suns J2EE transactional, vendor-neutral,

enterprise component architecture providing

Modelling of business entities as well as synchronous and

asynchronous processes

Persistence via explicit code (bean-managed) or via services of the EJBserver (container-managed)

Vendor neutrality and inter operability

XML driven deployment and configuration


JBs do not need a containerJBs are development componentsJBs are Classes with no argument constructor

JBs have a getand a setmethod on them

EJBs need a ContainerEJBs are deployable components

EJBs are assembled to form a complete Appl

EJBs are based on RMI IIOP and JNDI Technologies

EnterpriseJava Beans != Java Beans


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J2EE EJB Container/Server

20. EJB Overview

EJBPool

Client Process

Delegate

EJBClient

DelegateDelegate

Remoteinvoke

Homecreateremove

find

Network

EJB Impl

createremove

findinvoke

timeoutpassivate

activateloadstore

STUB STUB

LocalHome

create

removefind

Local

EJB Client

invoke

Delegate

EJB simplified distributed developmentDevelop EJB implementation logicDefine Home/Local Remote/Local interfaces

Container delegates client calls

Container manages resources/lifecycle/callbacks



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21. When to use EJB

If any of these requirements hold for your application

the application must be scalable and distributable Transactions will be required to ensure data integrity

the application will have a variety of clients



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22. Java Naming and

Directory Interface (JNDI)JNDI

Provides a standardized way of accessing resources in a distributed

environment

Protocol and naming service agnostic DNS

NDIS

LDAP

X.500

Implemented by the javax.naming package and three other packagesbelow it

javax.naming.InitialContext is the entry point to the EJB Server

bind associates a name with an object

lookup finds an object given the name



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23. EJB Specification

The EJB specification defines interfaces between

the EJB and its container the container and the application server

the container and the client



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24. EJB Roles

Service & Tool Provider

provides Server, Container and integrates with distributed facilities

Tools Provider

EJB Provider

Application Assembler

Application Server Provider

Deployer System Administratormaintains deployment

supplies tools builds application

develops EJBssupplies Application Server

deploys system

EJB Providercreates EJB components

Deployment Specialistdeploys apps and understands architecture issues

Application Assembler

assembles apps from per-built EJB comp



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25. EJB Design Approaches

EJB model is based on three basic design approaches forbuilding distributed component systems

Stateless server approach Session-oriented approach

Persistent Object approach


javax.ejb.EnterpriseBean interface

javax.ejb.EntityBean

The EJB specification provides these asStateless session Beans Message driven beans

Stateful session Beans Entity Beans

All EntityBeans All SessionBeans All MessageDrivenBeans

extends extends extends

implements implements implementsInterface Interface Interface

extends

javax.ejb.SessionBean javax.ejb.MessageDrivenBean

Implementing one of these interfacesindicates your JAVA class is an EJB.

It is only a marker Interfaceand there are no methods to

Implement.

As all these are extending thetwo Interfaces hence they have

the behavior of both the Interfaces.Serialization is the reason

EJB is distributable.

java.io.Serializable


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26. EJB Architecture

RMI/IIOP

Server A

App Server

EJB Container

creates

Naming Service suchas LDAP

Server B

JNDI

Initial Context

H

H

1

SERVICES

Naming Transaction Persistence Security

DB

EIS

MainFrames

3

2

4 5

6

7

8

9

10

11

HomeInterface

RemoteInterfaceApplicationClient

EJB(Business Logic Class)

We will write only this

delegates request

Container manages TRANSACTIONS, PERSISTENCE, SECURITY & POOLING

Container implements/autogenerates code for the Interfaces

Home Object(FACTORY)

EJB Object(Wrapper)

HomeObj

Stub

EJBObjStub


H

H

we have written


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creates EJB Object

27. EJB Flow Chart

C

ask JNDI Server for the Home Object 1

Remote Interface then wrapsa request to the Bean class

JNDI Server returns ref of Home Stub

ask Home for the EJB Object

returns reference of Remote Stub

C

goes to the JNDI Serverand gets the EJB Object

invokes a business methodthru Remote Stub

Clients receives the required info

End

Start

2

3

4

5

6

7

8

9



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App Server

EJB Container

28. Client View of EJB

ApplicationClient

RMI/IIOP

Entity Beaninstance

EJB Home orEJB Local Home

e.gBank account balancePurchase order

e.gStock trade messagesWork flow messages

e.gBank tellerCredit Card authorization

Message DrivenBean instance

Session Beaninstance


ENTITY BEANS are like NOUNS as they represent data or data related logic.

MESSAGE DRIVEN BEANS have message oriented logic.

If all the processing is done in the same Application server then we use

EJB Local(Object & Home) interfaces. Using local interfaces are optional.Local interfaces pass by REFERENCE and EJB (Object/Home) pass by VALUE.Using local interfaces avoids stubs, skeletons, network and so it is faster.

EJB Object orEJB Local Object

JMS Destination

SESSION BEANS are like VERBS as they represent action or business process related logic.


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29. EJB Client

EJB clients

utilizes the Java Naming and Directory Interface (JNDI) to look upfor the references to home interfaces

use home and remote EJB interfaces to utilize all EJB-basedfunctionality



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30. EJB Home Interface

EJB home interfaces extends javax.ejb.EJBHome

EJB home interfaces provide operations for clients to create EJBs remove EJBs find handles to EJB remote interface objects have its stub placed into JNDI at startup



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31. EJB Remote

EJB remote interfaces extends javax.ejb.EJBObject

EJB remote interfaces provide business-specific functionality of an EJB are similar to RMI Remote interface



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32. EJB Implementation

EJB implementation

Class in which EJB developer codes the business methodsdefined in the beans component interface(s) to provide any

application specific

business method invocation

creation removal finding activation passivation, database storage database loading logic



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33. Session Context

The Container has already reference to the bean

The bean interacts with the Container through SessionContext and

retrieves home interfaces

gets and sets transactions attributes

obtains security attribute

The setSessionContext method is used to inform the bean

about the session context



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34. Stateless Session EJB

Stateless session EJBs have the following behaviour

provide a single use service

do not maintain state on behalf of the client

are relatively short lived

do not survive EJB server crashes

any two instances of the same stateless session EJBtype are always identical

each instance can be shared by multiple clients



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35. Stateless Session EJBs View

EJB Impl Developer ViewEJB gets requests and generates responses

An instance can service multiple clients over time

EJB Client Developer View

creates it, uses it and then its done

EJB Container View

can pull instances from pool upon client request

can shrink/grow pool as needed

A few pooled beans can service thousands of clients

Client Process

EJBClient Remote

Home

Stateless Session

LocalHome LocalEJB Client

Network

Logic

input

outputEJB Pool


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Pool of equivalentmethod ready instances

ejbRemove()

ejbCreate()

Bean Instancedoes not exiist

Container decided itneeds more instancesin the pool to service clients

Client called remove()on the EJB object(or the client times out)

Class.newInstance()

setSessionContext()

Each method call is aninvocation from the

container to the Bean

36. Life Cycle of Stateless Session Bean

TransactionalBusiness Method

Client called anotherTransactional business methodon the EJB Object.


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37. Stateful Session EJBs View

EJB Impl Developer View

EJB gets requests and generates responses


EJB Client Developer Viewcreates it, uses it and then its done

EJB Container View

can pull instances from pool upon client request

can shrink/grow pool as needed

Client Process

EJBClient Remote

Home

Stateful Session

LocalHome Local

EJB Client

Network

Logic

input

outputEJB Pool

State


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If we implement Javax.ejb.SessionSynchronization then we need towrite these methods.

Bean instance is inthe passive state

Bean instance is readyto service method calls

Non-TransactionalBusiness Method

afterBegin()

ejbRemove()

ejbCreate(args)

Bean Instancedoes not exiistClient called create(args)

on the home Interface.

Containers limit ofinstantiated beansare reached, so it mustswap your bean out.

Client called remove()on the EJB object

(or the client times out)

Client called a transactionalbusiness method on theEJB Object

Client called anon-transactional businessmethod on the EJBObject

Class.newInstance()

setSessionContext()

ejbActivate()

beforeCompletion()

afterCompletion(true)

ejbPassivate()

Each method call is anInvocation from the


38 .Life Cycle of Stateful Session Bean

TransactionalBusiness Method

Client called anotherTransactional business methodon the EJB Object.

Client called a methodon a passivated bean, soContainer must swap your

Bean back in

Bean instance is withina transaction and readyto service method calls

afterCompletion(false)

If transaction endedin an abort.

If transaction endedin a commit..

Client times out

We need to write all

the methods that

are there in the

Implemented class


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39. Stateful vs Stateless


e.g

An EJB that unzips 100 bytes of data

An EJB that checks to see if a stock symbol is valid

e.g

An EJB that books a flight and rents a car at a travel agents

web site.

A stateful bean contains a conversational state that is

retained across method calls and transactions.

The create method takes arguments

e.g. create(String id) , create(int I , String id)There can be one or more arguments in a create method

A stateless bean does not have any state between calls toits methods.

The create method does not take arguments

e.g create()

There can be no arguments in a create method

Stateful Bean Stateless Bean

Method by method comparison can be seen in EJB20Matrix.doc at http://www.volantec.biz/cmp20.htm
http://www.volantec.biz/cmp20.htmhttp://www.volantec.biz/cmp20.htm


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40. Entity Bean

Entity Bean has the following behaviour

They are a representation of persistent data

They can survive a crash

Multiple clients can be using EJBs that represent thesame data

The EJB instance contains a copy of the data in thepersistent store

has a Primary key like in a Database record.



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Client Process

EJBClient Remote

Home

Entity Bean (BMP)

LocalHome LocalEJB Client

Network EJB Pool

41. BMP Entity EJBs


encapsulates data from a data source as objects

implements object-relational mapping (often JDBC)

implements inserts, deletes, queries and updates


creates, finds, updates and removes entity objects

EJB Container View

persists and manages concurrent access of instances

(BMP = Bean-Managed Persistence)

data

input

output

HandCodedLogic

Persisted objects (via hand-coding)


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42. Primary key class

Applicable only to entity beans

Uniquely differentiates instances sharing the sameEJBHome

Class must be a legal value type in RMI-IIOP Implements java.io.Serializable

all the members should be public

It should implement hashCode() and equals(.. ) methods

does not implement java.rmi.remote



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43. Shared Entity Bean

When multiple clients share an Entity EJB they

receive their own instance

share the underlying data

do not have to handle synchronization

App Server

EJB Container

CLIENT

Network

DB

CLIENTEJB

EJB



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ReadyejbLoad() ejbStore()

Pooled

Passivates the Bean

ejbCreate()

ejbPostCreate()

ejbRemove()

ejbHome() ejbFind()

Does not exiistContainer decided itneeds anotherEntity Bean insinstance

Container decided itdoesnt need the

Entity Bean instanceanymore

Client called a finderMethod on the homeinterface

Client called remove()on the EJB object(this will destroyDatabase data)

Container determinedthat the database is out ofsynch with the bean. TheBean needs to store itsData into the Database

Container determinedthat the database is out ofsynch with the bean. TheBean needs to load thenew Database data.

Client called create() onthe home interface (this willCreate new database data)

Client called instanceindependent ejbHome()

Business method

Activates the Bean

newInstance()

setEntityContext()

unsetEntityContext()

JVM will garbagecollectt and call finalize()

ejbActivate()

ejbLoad()

ejbStore()\

ejbPassivate()



44. Life Cycle of BMP Entity Bean

Business Method

Client called a businessmethod on a EJBObject

CMP E i EJB


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Client Process

EJBClient Remote

Home

Entity Bean (CMP)

LocalHome Local

EJB Client

Network EJB Pool

data

input

output

GeneratedLogic

45. CMP Entity EJBs


specifies CMP fields and relations among entities in DDs

specifies queries via EJB-QL in DDsuses tools to map standard object view to specific relational view


creates, finds, updates and removes entity objects

EJB Container View

persists and manages concurrent access of instances

(CMP = Container-Managed Persistence)

PersistenceDDs

Persisted objects (via container services)


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ReadyejbLoad() ejbStore()

Pooled

Passivates the Bean

ejbCreate()

ejbPostCreate()

ejbRemove()

ejbHome() ejbFind() or ejbSelect()

does not exiistContainer decided itneeds anotherEntity Bean in

Container decided itdoesnt need the

Entity Bean instanceanymore

Client called a findermethod on the homeInterface, or beancalled its own

ejbSelect()method to locateDatabase data

Client called remove()on the EJB object(this will destroyDatabase data)

Container determinedthat the database is out ofSynch with the bean. TheBean needs to store itsData into the Database

Container determinedthat the database is out ofSynch with the bean. TheBean needs to load thenew Database data.

Client called create() onthe home interface (this willcreate new database data)

Client called instanceindependent ejbHome()

Business method

Activates the Bean

newInstance()

setEntityContext()

unsetEntityContext()

JVM will garbagecollectt and call finalize()

ejbActivate()

ejbLoad()

ejbStore()\

ejbPassivate()



46. Life Cycle of CMP Entity Bean

Business Method

Or ejbSelect()

Client called a businessmethod on a EJBObject

NOTE : BMP has no ejbSelect()


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47. BMP vs CMP


We should start developing CMP beans, unless we require some kind of special bean, like multi-tables, that

cannot be completely realized with a single bean. Then when we realize that we need something more or that

we prefer handling the persistence (performance issue are the most common reason), we can change the bean

from a CMP to a BMP

Method by method comparison can be seen in EJB20Matrix.doc at http://www.volantec.biz/cmp20.htm

BMP offers a tactical approach

The developer takes care of handling persistenceBMP uses hard coded queries so we can optimize our

queries

Bean Managed Persistance

CMP is more strategic

Vendor takes care of everything by using O-R or OODBmappings using metadata.

A developer cannot optimize performance as the vedortakes care of it

Container Managed Persistance
http://www.volantec.biz/cmp20.htmhttp://www.volantec.biz/cmp20.htm


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48. Message Driven Bean

MDB has the following behaviour

Is stateless

is a JMS listener

when a JMS message arrives the methodonMessage() is executed

does not survive EJB server crashes

provides a single-use service

is relatively short lived is only a bean class no interfaces


49 M D i EJB


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Network

49. Message Driven EJBs

MessagingService

Message

QueueProducer Process

Message

Producer

Messaging

API

Message-Driven Bean

Handler Logic

input

MessageListener

MessageMessage


gets async requests via messaging paradigm-specific interface



Messages sent to endpoint & handled by messaging service

Specific to particular messaging paradigm used

EJB Container View

pulls instance from pool and delivers message

EJB Pool

Asynchronous messaging

0 Lif C l f M D i B


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Pooled

ejbCreate()

Does not exiistContainer decided itneeds anotherMessage DrivenBeanInstance

newInstance()

setMessageDrivenContext()



50. Life Cycle of Message Driven Bean

onMessage()

ejbRemove()


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51. Deployment

Deployment involves taking an EJB compliant bean and

creates XML that describes the EJB

packages the bean and XML into a Jar

generates container files for the EJB

configures properties of the EJB Server


BEAN Provider declares components middleware service requirements in a DEPLOYMENT DESCRIPTOR File.

Bean Provider describes how the Container should perform the LifeCycle Management, Persistence, Transaction and Security.

Declaring without programming helps the application assembler to change the XML file easily.


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52. Other interfaces and classes

Local interfaces are used for access within server context

javax.ejb.EJBLocalHome

javax.ejb.EJBLocalObject

Interfaces for serializing EJB references

HomeHandle - reference to EJBHome

Handle - reference to EJBObject

EJBMetaData interface provides mechanism to gatherinformation about the bean

reference to EJBHome object

Home, component interface and primary key classes

functions to determine bean type

E.g.:Inter component callsServlet invocation



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53. Exceptions

System exceptions are unchecked and propagated to theclient as java.rmi.RemoteException

Application exceptions are checked and propagated to the

client as a descendant of java.lang.Exception

EJB-specific exceptions include FinderException,CreateException, RemoteException (all in javax.ejbpackage)

Business method exceptions are at the discretion of theEJB developer



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EXAMPLE 1

STATELESS BEAN


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Using the Jar utility create an EJB Jarfile containing STEP 2 & STEP 3 files

54. Steps to Develop an EJB

C

Write .java files for the BEAN, HOMEand REMOTE interfaces

1

Write the Deployment descriptor

Compile all the STEP 1 files into.class files

Configure your EJB Server.E.g DB connections thread pooling etc

Then copy the EJB Jar file

C

Connect to your EJB by writing a testClient .java file compile it and run it .

Start your EJB container andconfirm that it has loadedthe EJB Jar file.

End

Start

2

3

4

6

7


5

Please download the trial Application Server software from the links provided on the Reference slide at the end.


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We will apply the previous slide flow chart procedure to make up our first EJB

example


These Interfaces comes with Java 2 Platformjava.io.Serializablejava.rmi.Remote

These Interfaces comes with EJB distributionJavax.ejb.EJBObject Javax.ejb.EJBHome

Javax.ejb.EnterpriseBean

Javax.ejb.SessonBean

Supplied by the Bean Provider / Developer/ We will write !

Hello world Remote Interface Hello World Home Interface

Hello World Bean

Implementation Class

Generated for us by the Container verdors tools

Hello world EJB Object Hello World Home Object

We need to CODE only this block

55. Hello World Object Model using RMI

NOTE : Object implementationis Vendor specific. The containermay implement eitherA single object for each client orA single object for all the clients.


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56. Hello World Object Model using LOCAL


These Interfaces comes with Java 2 Platformjava.io.Serializablejava.rmi.Remote

These Interfaces comes with EJB distribution

Javax.ejb.EJBLocalObject Javax.ejb.EJBLocalHomeJavax.ejb.EnterpriseBean

Javax.ejb.SessonBean

Supplied by the Bean Provider / Developer/ We will write !

Hello world LocalInterface Hello World Local Home InterfaceHello World Bean

Implementation Class

Generated for us by the Container verdors tools

Hello world EJB LocalObject Hello World Local Home Object

We need to CODE only this block

If all the processing is done in the same Application server then we use EJB Local (Object & Home) interfaces.Using local interfaces are optional. Local interfaces pass by REFERENCE and EJB (Object/Home) which is the

previous slide model you saw will pass by VALUE. As these interfaces does not extend Java.rmi.Remote theoverhead of creating stubs, skeletons,network traffic is avoided and so it is faster but the drawback is if ourcode relies on Local interfaces then we cannot call a bean remotely.

No Network soLOCAL IMROVESPERFORMANCE

NOTE : Object implementationis Vendor specific. The containermay implement eitherA single object for each client orA single object for all the clients.

57 HelloBean Home Interface


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57. HelloBean Home Interface

package examples ;

import java.io.Serializable;import java.rmi.RemoteException;

import javax.ejb.CreateException;

import javax.ejb.EJBHome;

public interface HelloHome extends javax.ejb.EJBHome

{Hello create() throws java.rmi.RemoteException,

javax.ejb.CreateException;

}


Rules of Java says package declaration should be at the beginning and ends with a semi colon

This is the Home Interface for the Home EJB (HelloBean).

This method creates/manufactures the EJBObject and returns it . This create() method corresponds to theejbCreate() method in HelloBean.Note In Home Interface we are throwing 2 exceptions Remote and Create .

NOTE : Rules of Interfaces states that there should be no implementation so you will find only method signatures.

Our interface HelloHome is extending EJBHome means it has all the behaviour of EJBHome

Interface methods should end with a semicolon ;

EJB Example requirement :When the client interacts with the EJB we need to return a Hello World greeting.

To provide an EJB with the above requirement we have to create Remote & HomeInterfaces , Bean Business logic class and a deployment descriptor. For clarity pleasesee the previous slide Hello World Object Model using RMI.

Importing the required files

As for every Interface we need implementation, so Container will implement (autogenerate code) for this Home Interface for us, which is the EJBHome Objec

58 HelloLocalHome Interface


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58. HelloLocalHome Interface

package examples ;

import javax.ejb.EJBLocalHome;


import javax.ejb.FinderException;

import java.util.Collection;

public interface HelloLocalHome extends javax.ejb.EJBLocalHome

{

HelloLocal create() throws javax.ejb.CreateException;

}Copyright 2004 Kanti Prasad All rights reserved


This is the LocalHome Interface for the Home EJB (HelloBean).

This method creates/manufactures the EJBLocal Object and returns it . This create() method corresponds to theejbCreate() method in HelloBean.Note In LocalHome Interface we are throwing only Create and not Remote exception as there is no network

So now lets code the HelloLocalHome Interface

NOTE : Rules ofInterfaces states that there should be no implementation so you will find only method signatures.

Our interface HelloLocalHome is extending EJBLocalHome means it has all the behaviour of EJBLocalHome

Interface methods should end with a semicolon ;As for every Interface we need implementation, so Container will implement (autogenerate code) for this Local Home for us, which is the LocalHome Object

59 HelloBean Remote Interface


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59. HelloBean Remote Interface

package examples ;

import java.util.*;

import javax.ejb.EJBObject;

import java.rmi.RemoteException;

public interface Hello extends javax.ejb.EJBObject

{public String hello() throws java.rmi.RemoteException;

}



Clients interact with the EJB Object through this Remote interface that is why we need to write this interface.

As for every Interface we need implementation, so Container will implement (autogenerate code) for this Remote Interface for us, which is the EJBObject

As our requirement wants a business logic to greet Hello World a single method would be sufficient .As Remote interface is used to interact with the Bean we need to mirror all the method signatures whatare there in a Bean class so that is why we are writing only one method in this Remote interface.Note EJB specification states that all remote calls should throw RemoteException so we are throwing it.

So lets code the Remote Interface


Our interface Hello is extending EJBObject means it has all the behaviour of EJBObject



60 HelloLocal Interface


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60. HelloLocal Interface

package examples ;

import javax.ejb.EJBLocalObject;

public interface HelloLocal extends javax.ejb.EJBLocalObject{

public String hello() ;

}



Clients interact with the EJB Object through this Local interface when there is no network involved..

As our requirement wants a business logic to greet Hello World a single method would be sufficient .As Local interface is used to interact with the Bean we need to mirror all the method signatures whatare there in a Bean class so that is why we are writing only one method in this Local interface.Note As there is no remote calls no Remote Exception is thrown


Our interface Hello is extending EJBLocalObject means it has all the behaviour of EJBLocalObject


As for every Interface we need implementation, so Container will implement (autogenerate code) for this Local Interface for us, which is the EJB Local Object

61 The Bean Class


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61. The Bean Class

package examples ;

import java.util.*;

import javax.ejb.*;

public class HelloBean implements javax.ejb.SessionBean

{

private SessionContext ctx;

public void ejbCreate() { System.out.println(ejbCreate()); }

public void ejbRemove() { System.out.println(ejbRemove());}

public void ejbActivate() { System.out.println(ejbActivate());}

public void ejbPassivate() { System.out.println(ejbPassivate()); }public void setSessionContext(javax.ejb.SessionContext ctx) {

this.ctx = ctx; }

public String hello() { System.out.println(Hello());

return Hello World! ; }

}



This is where we will code our Business logic

Note : this is a class and not an Interface like the other two (Home / Remote). This is implementing SessionBean so it is a Session Bean

This ejbCreate() corresponds to the Homeobject Create(). NOTE : in Stateless Bean no arguments are sent

So now lets code the actual EJB Class

As per the below note in red we need to write all the methods what are in javax.ejb.SessionBean .

Java does not support multiple inheritance so you can extend only one class. To overcome

this they had given us the Implementation option . So when we use implement we need toimplement or write all the methods what are there in the interface we implemented.

NOTE : If it is Entity Bean we will implement javax.ejb.EntityBean and if it is Message driven bean we will implement javax.ejb.MessagedrivenBean

These are calledManagement or

Call back methods

Our Business method which matchesour Remote Interface method signature

In Statelss Bean ejbActivateand ejbPassivate Do not apply

There is nothing much to clean up.

Storing the Context in a variable so that it can be queried later .NOTE : Because it is a Session Bean we are using setSessionContext for Entity Bean weuse setEntityContext and for Message Driven Bean we use setMessageDrivenContext.


62 The Deployment descriptor


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62. The Deployment descriptor

Hello

examples.HelloHome

examples.Hello

examples.HelloLocalHome

examples.HelloLocalexamples.HelloBean

Stateless

Container


As a Bean provider we need to specify the Middleware needs through this descriptor.

So now lets complete our EJB by writing the deployment descriptor.

XML Standard requirement

The nickname for this particular Bean

The fully qualified name of the Home Interface

The fully qualified name of the Remote Interface

The fully qualified name of the Local HomeInterfaceThe fully qualified name of the Local Interface

The fully qualified name of the EJB Class

Whether the session bean is stateful or stateless

THERE ARE MANYTOOLS WHICHCREATES THEDESCRIPTOR

FOR US

63 The Client


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63. The Client

package examples;

import javax.naming.Context;

import javax.naming.InitialContext;

import java.util.Properties;

public class HelloClient {

public static void main(String [] args) throws Exception{

Properties props = System.getProperties();

Context ctx = new InitialContext(props);

Object obj = ctx.lookup(HelloHome);

HelloHome home = (HelloHome) javax.rmi.PortableRemoteObject.narrow(

obj, HelloHome.class);Hello hello = home.create();

System.out.println(hello.hello());

hello.remove();}}



So now lets code our Client to access our simple stateless session bean.

importing the necessary files

As there is static key word this main method executes first before any other method in that class

Assigning props variable with properties information for JNDI initialization

Obtaining the JNDI initial context is the starting point for connection to a JNDI tree

Get a reference to the Home Object- the factory for Hello EJB Objects.

We are casting HelloHome here, as Home Objects are RMI-IIOP objects and so weNeed to use a special RMI-IIOP cast.

Use the factory to create the Hello EJB Object. We are then calling the hello() methodOn the EJB Object. The EJB object will delegate the call to the Bean,receive theResults and return it to us . We then print it on the screen.

Once we are done with the EJB Object, we can remove it.

By passing environment properties we will choose our JNDI driver,networklocation of the server etc.

NOTE : To call Local Interface you need not cast with the PortableRemoteObject. So the

block in red will be changed toObject obj = ctx.lookup(java:comp/env/HelloLocalHome); ( to get a ref to LocalHome Object)HelloLocalHome home = (HelloLocalHome)obj;


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64. EJB Jar File

PropertiesFile

Remote/LocalInterface

HomeLocalHomeInterface

EnterpriseBean Class

Deployment

Descriptor

Jar

Manifest

JarfileJar Creator

DEPLOYED


Jar file is a .ZIP compression format . META-MF file is a listing file automatically created by the Jar utility.

Or manually run C:\>Jar cf HelloWorld.jar *

The folder structure within the Ejb-jar file is

META-INF/MANIFEST.MFMETA-INF/ejb-jar.xmlexamples/HelloBean.classexamples/HelloLocalHome.classexamples/HelloLocal.classexamples/Hello.class

Please read the Deployment instructions provided by the Application server as it is Vendor specific


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65. EJB Application Assembler

.JAR .WARDeploymentDescriptor

DeploymentTool

Enterprise Archive

(.EAR Files)(Application.XML)

WEB ARCHIEVE (.war)

JSP

Servlets

HTMLWEB.XML

JAR ARC HIEVE (.jar)

HOMEEJB

REMOTEEJB-JAR.XML


Jarfile


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EXAMPLE 2

STATEFUL BEAN


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Stateful Session Remote Interface


package declaration should be in the beginning

Importing the required classes

There will not be any implementation in Interfaces

EJB spec says all remote interface methods need to throw remote exception

Our bean class CartBean methods are mirrored here

Remote Cart is extending EJBObject means Cart has all the behaviour of it

package samples.ejb.stateful.simple.ejb;

import java.util.*;

import javax.ejb.EJBObject;


import samples.ejb.stateful.simple.tools.BookException;

public interface Cart extends EJBObject

{

public void addBook(String title) throws RemoteException;

public void removeBook(String title) throws BookException, RemoteException;

public Vector getContents() throws RemoteException;

}


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Stateful Session Home Interface




There will not be any implementation in Interfaces

EJB spec says all Home interface methods need to throw remote & create exceptions

In a Stateful Bean you can have more than one create method taking arguments

CartHome is extending EJBHome means CartHome has all the behaviour of it

In our bean class CartBean these representejbCreate(String person) & ejbCreate(String person, String id)


import java.io.Serializable;



import javax.ejb.EJBHome;

public interface CartHome extends EJBHome {

Cart create(String person) throws RemoteException, CreateException;

Cart create(String person, String id) throws RemoteException,

CreateException;

}

St t f l S i B Cl


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Stateful Session Bean Class




as this is the Bean class we will implement the business logic here

CartBean Class is implementing sessionbean means this bean class is a session bean

NOTE : AS we are implementing and not extending we need to write all the methods that are there in the Sessionbean

We defined this method in the Cart remote interface.This also represents the Home create(String person) method


import java.util.*;

import javax.ejb.*;

import samples.ejb.stateful.simple.tools.BookException;

import samples.ejb.stateful.simple.tools.IdVerifier;

public class CartBean implements SessionBean {

String customerName;

String customerId;

Vector contents;

public void ejbCreate(String person) throws CreateException {

if (person == null) {

throw new CreateException("Null person not allowed.");

} else {

customerName = person;

}

customerId = "0";

contents = new Vector();

}

S f l S i B Cl


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// This block is a supporting business method written in idVerifier class



We defined this method in the Cart remote interfaceThis also represents the Home create(String person, String id) method we defined

The new operator is instantiating the instance of a class

We are calling the validate(id) method from the class ID Verifier

We defined this method in the Cart remote interface


We defined contents as a vector

public void ejbCreate(String person, String id) throws CreateException {

if (person == null) {throw new CreateException("Null person not allowed.");

} else {

customerName = person;

}

IdVerifier idChecker = new IdVerifier();

if (idChecker.validate(id)) {

customerId = id;

} else {

throw new CreateException("Invalid id: " + id);

}

contents = new Vector();

}

public void addBook(String title) {

contents.addElement(title);

}

public void removeBook(String title) throws BookException {

boolean result = contents.removeElement(title);

if (result == false) {

throw new BookException(title + " not in cart.");

}

}


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We need to write these methods as we are implementing SessionBean

Rules of implement states we need to implement all methods that are there in the implemented interface

Bean class constructor

public Vector getContents() {

return contents;

}

public CartBean() {}

public void ejbRemove() {}

public void ejbActivate() {}

public void ejbPassivate() {}

public void setSessionContext(SessionContext sc) {}

}


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CartJAR

CartEJB

CartEJB

samples.ejb.stateful.simple.ejb.CartHome

samples.ejb.stateful.simple.ejb.Cart

samples.ejb.stateful.simple.ejb.CartBean

Stateful

Container

Stateful Deployment Descriptor


required by any XML document

The nickname for this particular Bean

The fully qualified name of the Home Interface

The fully qualified name of the Remote Interface

The fully qualified name of the EJB Class

Bean type is mentioned here

Closing session and ejb

THERE ARE MANYTOOLS WHICHCREATES THEDESCRIPTOR

FOR US


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Passing Bean class methods and parameter info


CartEJB

Remote

getContents

Required

CartEJB

Remote

removeBook

java.lang.String

NotSupported


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CartEJB

Remote

addBook

java.lang.String

Required


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Stateful Session Client




Client class

As static is there this main method will execute first

The new operator is instantiating the instance of a class

Looking into JNDI

Casting with a suitable RMI IIOP object

Creating the object

Invoking the bean class method through remote interface Cart

adding books to the object


import java.util.*;

import javax.naming.Context;

import javax.naming.InitialContext;

import javax.rmi.PortableRemoteObject;

public class CartClient {

public static void main(String[] args) {

try {Context initial = new InitialContext();

Object objref = initial.lookup("java:comp/env/ejb/SimpleCart");

CartHome home =

(CartHome)PortableRemoteObject.narrow(objref,

CartHome.class);

Cart shoppingCart = home.create("Duke DeEarl","123");

shoppingCart.addBook("The Martian Chronicles");shoppingCart.addBook("2001 A Space Odyssey");

shoppingCart.addBook("The Left Hand of Darkness");

Vector bookList = new Vector();

bookList = shoppingCart.getContents();


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Stateful Session Client


We defined booklist as a vector

After storing in the variable title we are printing it

Removing a particular book using the bean class method removeBook throughremote interface Cartas we defined it this wayCart shoppingCart = home.create("Duke DeEarl","123");

We had written a new class BookException and using its method to catch any errors

Enumeration enumer = bookList.elements();

while (enumer.hasMoreElements()) {

String title = (String) enumer.nextElement();

System.out.println(title);

}

shoppingCart.removeBook("Alice in Wonderland");

shoppingCart.remove();

System.exit(0);

} catch (BookException ex) {

System.err.println("Caught a BookException: " + ex.getMessage());

System.exit(0);

} catch (Exception ex) {

System.err.println("Caught an unexpected exception!");

ex.printStackTrace();System.exit(1);

}

}

}


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Book Exception

package samples.ejb.stateful.simple.tools;

public class BookException extends Exception {

/**

* Default constructor.

*/public BookException() {

}

/**

* Constructor with a String as a parameter.

* @param msg message, describing the exception.

*/

public BookException(String msg) {

super(msg);}

}



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ID Verifier

package samples.ejb.stateful.simple.tools;

public class IdVerifier {

/**

* Default constructor.

*/public IdVerifier() {

}

public boolean validate(String id) {

boolean result = true;

for (int i = 0; i < id.length(); i++) {

if (Character.isDigit(id.charAt(i)) == false)

result = false;

}return result;

}

}



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ALL EXAMPLESCAN BE SEEN AT

http://www.weblogic.com/docs/examples/ejb/Package-examples.ejb.htmlhttp://my.execpc.com/~gopalan/java/entity.htmlhttp://java.sun.com/developer/onlineTraining/Beans/EJBTutorial/http://developers.sun.com/prodtech/javatools/jsstandard/reference/techart/entitybeans.html
http://www.weblogic.com/docs/examples/ejb/Package-examples.ejb.htmlhttp://my.execpc.com/~gopalan/java/entity.htmlhttp://java.sun.com/developer/onlineTraining/Beans/EJBTutorial/http://developers.sun.com/prodtech/javatools/jsstandard/reference/techart/entitybeans.htmlhttp://developers.sun.com/prodtech/javatools/jsstandard/reference/techart/entitybeans.htmlhttp://java.sun.com/developer/onlineTraining/Beans/EJBTutorial/http://my.execpc.com/~gopalan/java/entity.htmlhttp://www.weblogic.com/docs/examples/ejb/Package-examples.ejb.htmlhttp://www.weblogic.com/docs/examples/ejb/Package-examples.ejb.htmlhttp://www.weblogic.com/docs/examples/ejb/Package-examples.ejb.html


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EJB

Can implement the Remote or Local Interface

ActiveX

Uses Microsofts architecture for determining how clients

invocation requests are sent to components. DCOM used asunderlying transport mechanism

CORBAORB makes use of GIOP and other protocols to perform IPC

66. Component Comparison

Component Distributability



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EJB

exports operations through Remote Interface

ActiveX

exports operations in the same interface

CORBA

exports methods through Interface Repository


Components provide interfaces in the form of Operations



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EJB

Containers inject code to handle transactions, database management,

security, distributability and other customisable services. Containers

can be provided independent of App Server and EJB providers

ActiveX

Transactions, database management, legacy integration have to be coded

into the logic of the component. Security policy can be inherited from

NTLM. Transactions can be aided through MTS

CORBA

CORBAServices have different APIs. CORBAServices can be complicated

to code with. CORBAServices are not supported by all ORBs


Self Container Components


C C


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EJB

Properties are not explicitly exported but can be

mimicked through accessor operations

ActiveX

exports Properties in the same interface

CORBA

Properties not explicitly exported but can be

mimicked through attributes


Components provide interfaces in the form of Properties.


C C i


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EJB

Events supported through JMS with Message

Driven Bean

ActiveX

exports Events in the same interface

CORBAEvents supported through Event Service but cannotbe exported


Components provide interfaces in the form of Events.


71 C C i


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EJB

Incorporating the contents of an EJB can be done

in two ways: by having the new EJB use the services of an old

EJB as a direct client

or

by writing an EJB class that inherits from an

existing one

These two methods of leveragability give developers

maximum flexibility


Component Reusability


72 C C i


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Active X

Incorporating the contents of an ActiveX can be done

in two ways:

by having the new ActiveX use the services of anold ActiveX as a client

or

by Delegation

The Components being reused must be registered on

the development machine




73 C t C i


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CORBA

Every CORBA object has to have its own interfacedefinition

CORBA objects can use the services of other Objects

No mechanism for inheritance or Object reuse

inherently supported, though




74 C t C i


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EJB

Application Server makes multiple instances of EJB Objects. Client

contexts can be stored in different thread contexts. Different types

of EJBs identify levels of shareability.

ActiveX

uses Microsoft's inprocess/out-of-process architecture for sharing

multiple ActiveX components and Client components.

CORBA

ORB makes multiple instances of CORBA objects. Clients contexts are

managed by ORB but can behave differently based upon vendors

Implementation.


Components Shareability


75 Conclusion


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If you have any comments or appreciations then please email him [email protected], [email protected]

He likes to hear your feed back!

CONGRATULATIONS!Now you knowas much as heknow of EJB

75. Conclusion


We successfully completed a Tour on EJB . We looked at how an EJB is identified. How many

different types of EJBs are there and what each EJB type implements. Why

LocalInterfaces were introduced. We disected the EJB and went deeper into each part i.e. BEAN

Class, Remote Interface, EJB Object, Local Object, Local Interface, Home Object. We looked

Into the deployment descriptor and also seen all the files in EJBJar. We looked into each Beans

Methods and also learned why we needed those methods. We had done 2 different Beans

examples and we were directed to the Web links where all the examples are demonstrated. Once

you can get an idea of all the Interfaces, methods & exceptions raised, you can attempt to try

some examples to get familiar and master EJB. There are nearly 100s of Application servers

but in this presentation you can see a few majorly used AppServers sample implementation

web links. Just download any one of them and try out for yourself.

76. References
mailto:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]


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Application Servers download information . Most of them are either free or have a 60 day trial version

REDHAT Application Server and Examples

http://www.redhat.com/docs/manuals/rhaps/jonas-guide/

WebSphere downloads and examples

http://www-306.ibm.com/software/webservers/appserv/doc/v20dcadv/doc/howto/ep001.html

Application Server Information , EJB Documentation & Tutorials are found here

http://my.execpc.com/~gopalan/java/java_tutorial.html

EJB Documentation http://java.sun.com/products/ejb/javadoc-2_0-fr/

http://www.theserverside.com/Mastering Enterprise Java Beans

by Ed Roman , Scott Ambler & Tyler Jewel.

BEA WebLogic downloads and exampleshttp://commerce.bea.com/index.jsp , http://www.weblogic.com/docs/examples/index.html

http://dev2dev.bea.com/codelibrary/code/examples_ejb20.jsp


Most of EJBs related information can be seen at http://www.volantec.biz/ejb.htm

SUNs downloads and examples

http://developers.sun.com/prodtech/javatools/jsstandard/reference/docs/s1s5/partsuppliers.html

http://java.sun.com/j2se/1.4.2/download.html ,http://java.sun.com/j2ee/1.4/docs/tutorial/doc/

http://java.sun.com/developer/onlineTraining/EJBIntro/EJBIntro.html

For JBOSSOpen Source go to http://www.jboss.org/downloads/index

http://www.kevinboone.com/jboss_tut_1.html

Notes on Deploying on different Application Servers.

The Art of EJB Deployment http://www.javaworld.com/javaworld/jw-08-2001/jw-0803-ejb.html

Covers90 % of the

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