Enterprise Java Beans

EJB

A Component TechnologyA Component Technology A Component TechnologyA Component Technology

Enterprise Java BeansEnterprise Java Beans Enterprise Java BeansEnterprise Java Beans

A STAR or a different color

represents important

points to NOTE

1. 1. Learning objectivesLearning objectives1. 1. Learning objectivesLearning objectives

1. Component Technology characteristics

2. Standard Infrastructure needs

3. Application Servers

4. Containers

5. J2EE Architecture and its components

6. EJB Model, Overview & JNDI

7. EJB Specifications, Roles

8. EJB Design Approaches, Architecture

9. Types of Beans

10. EJB Interfaces & Session Contexts

11. Life cycles of different Beans

12. EJB Jar files & Deployment Descriptor

13. Sample examples

14. Components comparison

4. Component4. Component TechnologyTechnology4. Component4. Component TechnologyTechnology

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

5. 5. Component CharacteristicsComponent Characteristics5. 5. Component CharacteristicsComponent Characteristics

Properties Reusability

Operations Shareable

Events Distributable

Deployable Self Containment

Self description

Components Characteristics include

Components should have a mechanism for exporting

6. 6. Component P O E Component P O E 6. 6. Component P O E Component P O E

Properties

Operations

Events

7. Deployable Components7. Deployable Components7. Deployable Components7. Deployable Components

Components are operation independent of

• Hardware

• The underlying operating system

• Their Application Server

• The network protocol they use

8. Reusable Components8. Reusable Components8. Reusable Components8. Reusable Components

Component services can be used as a part of

business logic of other components

9. Shareable Components9. Shareable Components9. Shareable Components9. Shareable Components

If multiple clients are using a component

simultaneously, the component will provide

the same quality of service to all the clients

10. Distributable Components10. Distributable Components10. Distributable Components10. Distributable Components

Components should provide services to clients

running locally or remotely

Remote CLIENTS

EJB Container

EJB

Possible Remote

CLIENTS

Remote CLIENTS

Remote CLIENTS

Local CLIENTS

11. SelfContained Components11. SelfContained Components11. SelfContained Components11. SelfContained Components

Components should only contain the code

necessary to implement their services

Infrastructure services should be injected by

the execution environment

12. Standard Infrastructure Needs12. Standard Infrastructure Needs12. Standard Infrastructure Needs12. 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

13. Applicatoin Servers13. Applicatoin Servers13. Applicatoin Servers13. Applicatoin Servers

An application server provides the infrastructure and

services to run components/applications

J2EE based

solutions

Non-J2EE solutions

(PHP, Cold Fusion, Perl, etc.)

Microsoft Solutions

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

Application Server products are mostly

14. Object Pooling14. Object Pooling14. Object Pooling14. 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

CLIENTNetwork

DB

CLIENTEJB

EJB

EJBEJB

EJB

EJB

Pool

15. Directory of Application Servers15. Directory of Application Servers15. Directory of Application Servers15. Directory of Application Servers

Application Servers provide clients access to software or

other 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 athttp://www.devx.com/enterprise/html/16268

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

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



Container provides System services like

App Server

CLIENT

NetworkSTUB

Persistence Security Connection Pooling ThreadingTransaction

EJB Container

EJB

Fish cannot survive outside water &EJB’s cannot survive outside containers

Container interceptsrequests

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 apre developed Software

To increase capability.clustering is taken care

by the vendor

Implicit Middleware

gained through declaration

16. Container16. Container16. Container16. Container

17. 17. J2EE OverviewJ2EE Overview

Hardware Platform

Operating System Platform

J2EE Container/Server

Operating System Independence

Hardware Independence

Common Programming Services

Distributed Communication Services

J2SE RuntimeJ2SE Language/Interfaces

services standards component-based

Enterprise ComponentsApplication Server

Independence

Database Independence

Web Server Independence

Enterprise Resource Management Services

Deployment/ConfigurationManagement Services

J2EE Interfaces

Data

DeploymentDescriptors (DDs)

DeploymentDescriptors (DDs)

DeployTools

J2SE

Application ClientContainer

DBSAAJ

JAX-RPC

CONJMX

JMS

WEBS

JAXR

JDBC

MgmtDAO

Client

J2SE

SAAJ

JAX-RPC

JTA

CONJMX

Mgmt

JAF

JavaMail

JMS

JACC

WEBS

JAXR

JNDI

JDBC

AppletContainer

J2SE

HTTP/S

HTTP/S

Web Container

JSP ServletApplet

2 TIER

3 TIER

SAAJ

JAX-RPC

JTA

CONJMX

Mgmt

JAF

JavaMail

JMS

JACC

WEBS

JAXR

JNDI

JDBC

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. 18. J2EE 1.4 APIsJ2EE 1.4 APIs18. 18. J2EE 1.4 APIsJ2EE 1.4 APIs

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

JSP Servlet ENGINE

19. 19. Enterprise JavaBeans ModelEnterprise JavaBeans Model19. 19. Enterprise JavaBeans ModelEnterprise JavaBeans Model

EJB is Sun’s 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 EJB

server (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 constructorJBs have a get and a set method 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

J2EE EJB Container/Server

20. 20. EJB OverviewEJB Overview

EJB Pool

Client Process

Delegate

EJB Client

DelegateDelegate

Remoteinvoke

Homecreateremove

find

Network

EJB Implcreateremove

findinvoke

timeoutpassivateactivate

loadstore

STUB STUB

LocalHome

createremove

find

Local

EJB Client

invoke

Delegate

EJB simplified distributed development–Develop EJB implementation logic–Define Home/Local Remote/Local interfaces–Container delegates client calls–Container manages resources/lifecycle/callbacks

21. 21. When to use EJBWhen to use EJB21. 21. When to use EJBWhen 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

22. 22. Java Naming and Java Naming and Directory Interface (JNDI)Directory Interface (JNDI)

22. 22. Java Naming and Java Naming and Directory Interface (JNDI)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 packages

below 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

23. EJB Specification23. EJB Specification23. EJB Specification23. EJB Specification

The EJB specification defines interfaces between

• the EJB and its container

• the container and the application server

• the container and the client

24. EJB Roles24. EJB Roles24. EJB Roles24. EJB Roles

Service & Tool Providerprovides 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 Provider

creates EJB componentsDeployment Specialistdeploys apps and understands architecture issues

Application Assemblerassembles apps from per-built EJB comp

25. EJB Design Approaches25. EJB Design Approaches25. EJB Design Approaches25. EJB Design ApproachesEJB model is based on three basic design approaches for

building distributed component systemsStateless server approach Session-oriented approach

Persistent Object approach

javax.ejb.EnterpriseBean interface

javax.ejb.EntityBean

The EJB specification provides these as Stateless 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 interfaces indicates your JAVA class is an EJB.

It is only a marker Interfaceand there are no methods to

Implement.

As all these are extending the two Interfaces hence they have

the behavior of both the Interfaces.Serialization is the reason EJB is distributable.

java.io.Serializable

26.26. EJB ArchitectureEJB Architecture26.26. EJB ArchitectureEJB Architecture

RMI/IIOP

Server A

App Server

EJB Container

creates

Naming Service such as LDAP

Server B

JNDI Initial Context

H

H

1

SERVICES Naming Transaction Persistence Security

DB

EIS

MainFrames

3

2

4 56

7

8

9

10

11

HomeInterface

RemoteInterfaceApplication

Client

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)

Home Obj Stub

EJB Obj Stub

H

H

we have written

creates EJB Object

27. 27. EJB Flow ChartEJB Flow Chart27. 27. EJB Flow ChartEJB Flow Chart

C

ask JNDI Server for the Home Object 1

Remote Interface then wraps a 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 Server and gets the EJB Object

invokes a business method thru Remote Stub

Clients receives the required info

End

Start

2

3

4

5

6

7

8

9

App Server

EJB Container

28. 28. Client View of Client View of EJB EJB 28. 28. Client View of Client View of EJB EJB

Application Client

RMI/IIOP

Entity Beaninstance

EJB Home orEJB Local Home

e.g•Bank account balance•Purchase order

e.g•Stock trade messages•Work flow messages

e.g•Bank teller•Credit 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.

29. 29. EJB ClientEJB Client29. 29. EJB ClientEJB 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

30. 30. EJB Home InterfaceEJB Home Interface30. 30. EJB Home InterfaceEJB 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

31. 31. EJB RemoteEJB Remote31. 31. EJB RemoteEJB Remote

EJB remote interfaces extends javax.ejb.EJBObject

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

32. 32. EJB ImplementationEJB Implementation32. 32. EJB ImplementationEJB Implementation

EJB implementation

Class in which EJB developer codes the business methods

defined in the bean’s component interface(s) to provide any

application specific

• business method invocation• creation• removal• finding• activation• passivation, database storage• database loading logic

33. Session Context33. Session Context33. Session Context33. 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

34. Stateless Session EJB34. Stateless Session EJB34. Stateless Session EJB34. 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 EJB type are always identical

• each instance can be shared by multiple clients


35. 35. Stateless Session EJBsStateless Session EJBs View View

EJB Impl Developer View

EJB gets requests and generates responses

An instance can service multiple clients over time

EJB Client Developer View

creates it, uses it and then it’s 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

EJB Client Remote

Home

Stateless SessionLocalHome Local

EJB Client

Network

Logic

input

outputEJB Pool

Pool of equivalentmethod ready instances

ejbRemove()

ejbCreate()

Bean Instancedoes not exiist

Container decided it needs 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 an invocation from the

container to the Bean

36. Life Cycle 36. Life Cycle of of Stateless SessionStateless Session Bean Bean

TransactionalBusiness Method

Client called another Transactional business methodon the EJB Object.


37. 37. StateStatefulful Session EJBs Session EJBs View View


EJB gets requests and generates responses



creates it, uses it and then it’s done

EJB Container View

can pull instances from pool upon client request

can shrink/grow pool as needed

Client Process

EJB Client Remote

Home

Stateful Session

LocalHome Local

EJB Client

Network

Logic

input

outputEJB Pool

State

If we implement Javax.ejb.SessionSynchronization then we need to write these methods.

Bean instance is in the 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.

Container’s 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 transactional business method on theEJB Object

Client called a non-transactional businessmethod on the EJBObject

Class.newInstance()

setSessionContext()

ejbActivate()

beforeCompletion()

afterCompletion(true)

ejbPassivate()

Each method call is an Invocation from the


38 .Life Cycle 38 .Life Cycle of of Stateful SessionStateful Session Bean Bean

TransactionalBusiness Method

Client called another Transactional business methodon the EJB Object.

Client called a methodon a passivated bean, so Container must swap your Bean back in

Bean instance is withina transaction and ready to 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

39. Stateful vs Stateless39. Stateful vs Stateless39. Stateful vs Stateless39. 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 agent’s

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 to its 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.htm

40. Entity Bean40. Entity Bean40. Entity Bean40. 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 the same data

• The EJB instance contains a copy of the data in the persistent store

• has a Primary key like in a Database record.


Client Process

EJB Client Remote

Home

Entity Bean (BMP)

LocalHome Local

EJB Client

Network EJB Pool

41. 41. BMP Entity EJBsBMP 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)

42. 42. Primary key classPrimary key class42. 42. Primary key classPrimary key class

• Applicable only to entity beans Uniquely differentiates instances sharing the same

EJBHome 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

43. Shared Entity Bean43. Shared Entity Bean43. Shared Entity Bean43. 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

CLIENTNetwork

DB

CLIENTEJB

EJB

ReadyejbLoad() ejbStore()

Pooled

Passivates the Bean

ejbCreate()

ejbPostCreate()

ejbRemove()

ejbHome() ejbFind()

Does not exiistContainer decided itneeds another Entity Bean insinstance

Container decided itdoesn’t need the Entity Bean instanceanymore

Client called a finderMethod on the home interface

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

Container determinedthat the database is out ofsynch with the bean. The Bean needs to store its Data into the Database

Container determinedthat the database is out ofsynch with the bean. The Bean needs to load the new Database data.

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

Client called instanceindependent ejbHome()Business method

Activates the Bean

newInstance()

setEntityContext()

unsetEntityContext()

JVM will garbage collectt and call finalize()

ejbActivate()

ejbLoad()

ejbStore()\

ejbPassivate()



44. Life Cycle 44. Life Cycle of of BMP BMP Entity BeanEntity Bean

Business Method

Client called a business method on a EJBObject


Client Process

EJB Client Remote

Home

Entity Bean (CMP)

LocalHome Local

EJB Client

Network EJB Pool

data

input

output

GeneratedLogic

45. 45. CMP Entity EJBsCMP Entity EJBs


specifies CMP fields and relations among entities in DDs

specifies queries via EJB-QL in DDs

uses 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

PersistenceDDs

Persisted objects (via container services)

ReadyejbLoad() ejbStore()

Pooled

Passivates the Bean

ejbCreate()

ejbPostCreate()

ejbRemove()

ejbHome() ejbFind() or ejbSelect()

does not exiistContainer decided itneeds another Entity Bean in

Container decided itdoesn’t need the Entity Bean instanceanymore

Client called a findermethod on the home Interface, or bean called its own ejbSelect() method to locate Database data

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

Container determinedthat the database is out ofSynch with the bean. The Bean needs to store its Data into the Database

Container determinedthat the database is out ofSynch with the bean. The Bean needs to load the new Database data.

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

Client called instanceindependent ejbHome()Business method

Activates the Bean

newInstance()

setEntityContext()

unsetEntityContext()

JVM will garbage collectt and call finalize()

ejbActivate()

ejbLoad()

ejbStore()\

ejbPassivate()



46. Life Cycle 46. Life Cycle of of CMP CMP Entity BeanEntity Bean

Business MethodOr ejbSelect()

Client called a business method on a EJBObject

NOTE : BMP has no ejbSelect()

47. BMP vs CMP47. BMP vs CMP47. BMP vs CMP47. 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 persistence

BMP 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 vedor takes care of it

Container Managed Persistance

http://www.volantec.biz/cmp20.htm

48. Message Driven Bean48. Message Driven Bean48. Message Driven Bean48. Message Driven Bean

MDB has the following behaviour• Is stateless• is a JMS listener• when a JMS message arrives the method

onMessage() is executed• does not survive EJB server crashes• provides a single-use service• is relatively short lived• is only a bean class – no interfaces


Network

49. 49. Message Driven EJBsMessage Driven EJBs

Messaging Service

MessageQueueProducer Process

MessageProducer

Messaging

API

Message-Driven BeanHandler Logic

input

MessageListener

Message Message


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

Pooled

ejbCreate()

Does not exiistContainer decided itneeds another Message DrivenBean Instance

newInstance()

setMessageDrivenContext()



50. Life Cycle 50. Life Cycle of of Message DrivenMessage Driven Bean Bean

onMessage()

ejbRemove()

51. Deployment51. Deployment51. Deployment51. 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.

52. 52. Other interfaces and classesOther interfaces and classes52. 52. Other interfaces and classesOther 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 gather information about the bean reference to EJBHome object Home, component interface and primary key classes functions to determine bean type

E.g.:•Inter component calls•Servlet invocation

53. 53. ExceptionsExceptions53. 53. ExceptionsExceptions

System exceptions are unchecked and propagated to the client 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.ejb package)

Business method exceptions are at the discretion of the EJB developer

EXAMPLE 1STATELESS BEAN

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

54. Steps to Develop an EJB54. Steps to Develop an EJB54. Steps to Develop an EJB54. Steps to Develop an EJB

C

Write .java files for the BEAN, HOME and 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 and confirm that it has loaded the 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.

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 distribution Javax.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 InterfaceHello World Bean

Implementation Class

Generated for us by the Container verdor’s tools

Hello world EJB Object Hello World Home Object

We need to CODE only this block

55. 55. Hello World Object Model using RMIHello World Object Model using RMI55. 55. Hello World Object Model using RMIHello World Object Model using RMI

NOTE : Object implementation is Vendor specific. The container may implement eitherA single object for each client or A single object for all the clients.

56. Hello World Object Model using LOCAL56. Hello World Object Model using LOCAL56. Hello World Object Model using LOCAL56. 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.EJBLocalHome

Javax.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 verdor’s 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 the overhead of creating stubs, skeletons,network traffic is avoided and so it is faster but the drawback is if our code relies on Local interfaces then we cannot call a bean remotely.

No Network so LOCAL IMROVES PERFORMANCE

NOTE : Object implementation is Vendor specific. The container may implement eitherA single object for each client or A single object for all the clients.

57. HelloBean Home Interface57. HelloBean Home Interface57. HelloBean Home Interface57. 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 the ejbCreate() 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 & Home Interfaces , 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 Object

58. HelloLocalHome Interface58. HelloLocalHome Interface58. HelloLocalHome Interface58. 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;

}


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 the ejbCreate() 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


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 Interface59. HelloBean Remote Interface59. HelloBean Remote Interface59. HelloBean Remote Interface

package examples ;

import java.util.*;

import javax.ejb.EJBObject;


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 what are 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 Interface60. HelloLocal Interface60. HelloLocal Interface60. 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 what are 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 Class61. The Bean Class61. The Bean Class61. 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 to implement 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 called Management 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 we use setEntityContext and for Message Driven Bean we use setMessageDrivenContext.


62. The Deployment descriptor62. The Deployment descriptor62. The Deployment descriptor62. The Deployment descriptor

<!DOCTYPE ejb-jar PUBLIC “-//Sun Microsystems, Inc. // DTD Enterprise JavaBeans 2.0 // EN “ “ http://java.sun.com.dtd/ejb-jar_2_0.dtd”>

<ejb-jar>

<enterprise-beans>

<session>

<ejb-name> Hello </ejb-name>

<home>examples.HelloHome</home>

<remote>examples.Hello</remote>

<local-home>examples.HelloLocalHome</local-home>

<local>examples.HelloLocal</local>

<ejb-class>examples.HelloBean</ejb-class>

<session-type>Stateless</session-type>

<transaction-type>Container</transaction-type>

</session>

</enterprise-beans>

</ejb-jar>

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 MANY TOOLS WHICH CREATES THE DESCRIPTOR

FOR US

63. The Client 63. The Client 63. The Client 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,network location 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;

64. EJB Jar File64. EJB Jar File64. EJB Jar File64. EJB Jar File

PropertiesFile

Remote/LocalInterface

HomeLocalHomeInterface

EnterpriseBean Class

DeploymentDescriptor

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

65. EJB Application Assembler65. EJB Application Assembler65. EJB Application Assembler65. EJB Application Assembler

.JAR .WARDeployment Descriptor

Deployment Tool

Enterprise Archive(.EAR Files)

(Application.XML)

WEB ARCHIEVE (.war)

JSPServlets

HTMLWEB.XML

JAR ARC HIEVE (.jar)

HOMEEJB

REMOTEEJB-JAR.XML

Jarfile

EXAMPLE 2 STATEFUL BEAN

66. Stateful Session Remote Interface66. Stateful Session Remote Interface66. Stateful Session Remote Interface66. 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;

}

67. Stateful Session Home Interface67. Stateful Session Home Interface67. Stateful Session Home Interface67. 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 represent ejbCreate(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;

}

68. Stateful Session Bean Class68. Stateful Session Bean Class68. Stateful Session Bean Class68. 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();

}

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


We defined this method in the Cart remote interface This 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.");

}

}



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) {}

}

<?xml version="1.0" encoding="UTF-8"?>



<ejb-jar version="2.1" xmlns="http://java.sun.com/xml/ns/j2ee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee http://java.sun.com/xml/ns/j2ee/ejb-jar_2_1.xsd">

<display-name>CartJAR</display-name>

<enterprise-beans>

<session>

<display-name>CartEJB</display-name>

<ejb-name>CartEJB</ejb-name>

<home>samples.ejb.stateful.simple.ejb.CartHome</home>

<remote>samples.ejb.stateful.simple.ejb.Cart</remote>

<ejb-class>samples.ejb.stateful.simple.ejb.CartBean</ejb-class>

<session-type>Stateful</session-type>

<transaction-type>Container</transaction-type>

<security-identity>

<use-caller-identity/>

</security-identity>

</session>

</enterprise-beans>

71. Stateful Deployment Descriptor71. Stateful Deployment Descriptor71. Stateful Deployment Descriptor71. 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 MANY TOOLS WHICH CREATES THE DESCRIPTOR

FOR US


Passing Bean class methods and parameter info


<assembly-descriptor>

<container-transaction>

<method>


<method-intf>Remote</method-intf>

<method-name>getContents</method-name>

</method>

<trans-attribute>Required</trans-attribute>

</container-transaction>


<method>



<method-name>removeBook</method-name>

<method-params>

<method-param>java.lang.String</method-param>

</method-params>

</method>

<trans-attribute>NotSupported</trans-attribute>





<method>



<method-name>addBook</method-name>

<method-params>

<method-param>java.lang.String</method-param>

</method-params>

</method>

<trans-attribute>Required</trans-attribute>


</assembly-descriptor>

</ejb-jar>

74. Stateful Session Client74. Stateful Session Client74. Stateful Session Client74. Stateful Session Clientpackage declaration should be in the beginning


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();

75. Stateful Session Client75. Stateful Session Client75. Stateful Session Client75. 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 through remote interface Cart –as 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);

}

}

}

76. Book Exception76. Book Exception76. Book Exception76. Book Exception

package samples.ejb.stateful.simple.tools;

public class BookException extends Exception {

/**

* Default constructor.

*/

public BookException() {

}

/**

* Constructor with a <code>String<code> as a parameter.

* @param msg message, describing the exception.

*/

public BookException(String msg) {

super(msg);

}

}

77. ID Verifier77. ID Verifier77. ID Verifier77. 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;

}

}

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.html

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

http://java.sun.com/developer/onlineTraining/Beans/EJBTutorial/

http://developers.sun.com/prodtech/javatools/jsstandard/reference/techart/entitybeans.html

EJB

Can implement the Remote or Local Interface

ActiveX

Uses Microsoft’s architecture for determining how clients’

invocation requests are sent to components. DCOM used as underlying transport mechanism

CORBAORB makes use of GIOP and other protocols to perform IPC

78. 78. Component Component ComparisonComparison78. 78. Component Component ComparisonComparison

Component Distributability

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

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

ActiveXTransactions, 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

CORBACORBAServices have different APIs. CORBAServices can be complicated

to code with. CORBAServices are not supported by all ORBs


Self – Container Components

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.

EJB

Events supported through JMS with Message

Driven Bean

ActiveX

exports Events in the same interface

CORBAEvents supported through Event Service but cannot be exported


Components provide interfaces in the form of Events.

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

Active X

Incorporating the contents of an ActiveX can be done

in two ways:

• by having the new ActiveX use the services of an old ActiveX as a client

or • by Delegation

The Components being reused must be registered on

the development machine



CORBA

Every CORBA object has to have its own interface definition

CORBA objects can use the services of other Objects

No mechanism for inheritance or Object reuse inherently supported, though



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.

ActiveXuses Microsoft's in–process/out-of-process architecture for sharing

multiple ActiveX components and Client components.

CORBAORB makes multiple instances of CORBA objects. Clients’ contexts are

managed by ORB but can behave differently based upon vendor’s

Implementation.


Components Shareability

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