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Enterprise Java BeansEnterprise Java Beans

Technology ConsultingTechnology Consulting

PramatiPramatiTechnologiesTechnologies

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Agenda

What is an EJBWhat is an EJB

Bean BasicsBean Basics

Component ContractComponent Contract

Bean VarietiesBean Varieties

Session Beans

Entity Beans

Message Driven Beans

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What is an EJB ?

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Bean is a component

A server-side componentA server-side component

Contains business logic that operates on some temporaryContains business logic that operates on some temporarydata or permanent databasedata or permanent database

Is customizable to the target environmentIs customizable to the target environment

Is re-usableIs re-usable

Is truly platform-independentIs truly platform-independent

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A Typical Bean at Work

Account Bean

open ()

deposit ()

withdraw ()balance ()

close ()

Name

Address

Amount

open ()

deposit ()

withdraw ()balance ()

close ()

Name

Address

Amount

Client

Client

Database

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So, what is an EJB?

Ready-to-use Java componentReady-to-use Java component Being Java implies portability, inter-operability

Can be assembled into a distributed multi-tier applicationCan be assembled into a distributed multi-tier application

Handles threading, transactionsHandles threading, transactions Manages state and resourcesManages state and resources

Simplifies the development of complex enterpriseSimplifies the development of complex enterpriseapplicationsapplications

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EJB dumbs down complexity

App

lica

tioncom

plex

ity Corba, COM

EJB

state mgmt

distributed txn

load balancing

thread

concurrencysecurity

single user

shared db

Componentization

Multi-tier architecture

Desktop Network Web Large scale enterprise apps

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Where EJB fits in Multi-tier

Presentation ObjectsPresentation Objects

Business Logic ObjectsBusiness Logic Objects

Data ObjectsData Objects

ClientClient

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Benefits

Pure Java implies portabilityPure Java implies portability

exchange components without giving away the source

Provides interoperabilityProvides interoperability

assemble components from anywhere, can all work together

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Operational Benefits from EJB

Transaction management serviceTransaction management service

Distributed Transaction supportDistributed Transaction support

PortabilityPortability

ScalabilityScalability

Integration with CORBA possibleIntegration with CORBA possible

Support from multiple vendorsSupport from multiple vendors

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What Does EJB Really Define?

Component architectureComponent architecture

Specification to write components using JavaSpecification to write components using Java

Specification to component server developersSpecification to component server developers

Contract between developer roles in a components-basedContract between developer roles in a components-basedapplication projectapplication project

The basis of components used in distributed transaction-

oriented enterprise applications

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The Componentized Application

Application now consists of several re-usable componentsApplication now consists of several re-usable components

InstancesInstances of components created at run-time for a clientof components created at run-time for a client

Common object for all instances of the component, usuallyCommon object for all instances of the component, usuallycalled the Factory Objectcalled the Factory Object

EJB calls it Home Object

Common place where client can locate thisCommon place where client can locate this Home ObjectHome Object

Objects located from a remote client throughObjects located from a remote client through JNDIJNDI (Java(Java

Naming and Directory Interface) serviceNaming and Directory Interface) service

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Application Server provides

JNDI based naming serviceJNDI based naming service

Implementation of Bean, Home and RemoteImplementation of Bean, Home and Remote

Complete Life Cycle ManagementComplete Life Cycle Management

Resource pooling - beans, db connections, threads...Resource pooling - beans, db connections, threads...

Object persistenceObject persistence

Transaction managementTransaction management

Secured access to beansSecured access to beans

Scalability and availabilityScalability and availability

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EJB: Core of J2EE Architecture

J2EE ServerJ2EE Server

EJB

Container

EJB

Container

Web

Container

JSP

Servlets

Java

client

BeansBeans

rmiHTML

client

http

Business logicBusiness logic

EJB Component

server

EJB Component

server

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The Architecture Scenario

Create individual business and web componentsCreate individual business and web components

Assemble these components into an applicationAssemble these components into an application

Deploy application on an application serverDeploy application on an application server

Run application on target environmentRun application on target environment

Bean ProviderBean Provider

AssemblerAssembler

Server ProviderServer Provider

Container ProviderContainer Provider

DeployerDeployer

Application

Responsibilities

Application

Responsibilities

Appointed forResponsibilitiesAppointed forResponsibilities

AdministratorAdministrator

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EJB Architecture Roles Six roles in application development and deployment lifeSix roles in application development and deployment life

cyclecycle

Bean Provider

Application Assembler

Server Provider

Container Provider

Deployer

System Administrator

Each role performed by a different partyEach role performed by a different party Product of one role compatible with anotherProduct of one role compatible with another

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DeployerDeployerSystem

Administrator

System

Administrator

Server

Provider

Server

Provider

AssemblerAssemblerBean

Developer

Bean

Developer

Container

Provider

Container

Provider

How the Roles Collaborate

Create Assemble Deploy

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Bean Basics

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Creating the Bean Instance

Look up for the Home Object through JNDILook up for the Home Object through JNDI Get the referenceGet the reference

CallCall create() methodcreate() method

The server generates the code for remote access usingThe server generates the code for remote access using RMIRMI(Remote Method Invocation).(Remote Method Invocation).

The RMI code in the form of stub and skeleton:The RMI code in the form of stub and skeleton:

establishes connection,

marshals/unmarshals

places remote method calls

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...Bean Instance

Client

Component ServerComponent Server

Name ServerName Server

Home

Object Client calls create()

Bean places reference to

Home Object under JNDI

Naming service

Client locates Home

Object

Bean Instance created Bean

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Using the Component

Client


Remote Object

Client gets reference to

EJB Object after create()

Client calls business

method on EJB ObjectBean

EJB Object delegates to

bean instance

Writing business methods is the

bean developers main work

All bean methods are exposed asremote accessible functions by

the EJB Object

Writing business methods is the

bean developers main work

All bean methods are exposed asremote accessible functions by

the EJB Object

Business

Methods

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Locating a Component

Client


Remote Object

Bean

Home Object finds the

Bean creates aninstance

Client calls find() method

on Home Object

Returns reference to

the EJB Object of

new Bean instance

Find method revives instances of

bean at a point after creation

Bean writer writes Find methods

Find method is exposed through

the Home Object

Find method revives instances of

bean at a point after creation

Bean writer writes Find methods Find method is exposed through

the Home Object

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A Typical Bean Application

Client


Account1

Account2

Teller

Session Bean

Entity Bean

A typical application requires a collection of bean classes deployed on the server.

Beans could be of three types: Session Beans - that represent process objects

Entity Beans - that represent data objects Message Driven Beans that act as message consumers

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Benefits of Beans - A Recall

Less programming complexityLess programming complexity

Focus on business logic and plumbing code is availableFocus on business logic and plumbing code is available

Enterprise Level Services like Transaction, Security,Enterprise Level Services like Transaction, Security,

Naming availableNaming available Container Managed PersistenceContainer Managed Persistence

Server Managing precious resourcesServer Managing precious resources

Very high level of reuseVery high level of reuse PortabilityPortability

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Component Contract

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Container: The Host on the Server

Hosts multiple EJBsHosts multiple EJBs

Provides life-cycle management for EJB create, locate, remove,Provides life-cycle management for EJB create, locate, remove,

remote method callsremote method calls Provides high-performance in handling large pool of bean instancesProvides high-performance in handling large pool of bean instances

ledgerledgeraccount1account1

tellertelleraccount2account2

EJB

Container

Beans

Naming Txn Security

interfaces

EJB

Server

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Client, Container & Bean Work... Component Server hosts the containerComponent Server hosts the container

The Container hosts the beans and provides infrastructural support forThe Container hosts the beans and provides infrastructural support for

the beans to functionthe beans to function

Beans can be deployed in any container that conforms with EJBBeans can be deployed in any container that conforms with EJB

specificationsspecifications

Bean instance created, managed at run-time by the containerBean instance created, managed at run-time by the container

Container mediates client access to the EJBContainer mediates client access to the EJB

These activities are enabled by non-negotiable contracts

among the client, component and container

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Via Contracts Client-view contractClient-view contract

Component contractComponent contract

EJB-jar fileEJB-jar file


ContainerContainer

Bean InstanceBean Instance

Component

Contract

Component

Contract

ClientClientClient

View

Contract

Client

View

Contract

Bean class files, interfacesBean class files, interfaces

Deployment descriptorDeployment descriptorEJB-jarEJB-jar

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Client-view contract

Contract between client and containerContract between client and container Uniform application development model forUniform application development model for

greater re-use of componentsgreater re-use of components

View sharing by local and remote programsView sharing by local and remote programs

The Client can be:The Client can be:

another EJB deployed in same or another container

a Java program, an applet or a Servlet

mapped to non-Java clients like CORBA clients

Home InterfaceHome Interface

Remote InterfaceRemote Interface

Object IdentityObject Identity

Metadata InterfaceMetadata Interface

Container HandleContainer Handle

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Component contract

Between an EJB and the container it is hosted byBetween an EJB and the container it is hosted by This contract needs responsibilities to be shared by:This contract needs responsibilities to be shared by:

the bean provider

the container provider

Container

providers

responsibilitiesBean

providers

responsibilities

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Bean providers responsibility

Implement business methods in the beanImplement business methods in the bean ImplementImplement ejbCreate, ejbPostCreateejbCreate, ejbPostCreate andand ejbRemoveejbRemove

methods, andmethods, and ejbFindejbFindmethod (in the case of bean managedmethod (in the case of bean managedpersistence)persistence)

Define home and remote interfaces of the beanDefine home and remote interfaces of the bean

Implement container callbacks defined in theImplement container callbacks defined in thejavax.ejb.Sessionjavax.ejb.Session bean interfacebean interface

optionally thejavax.ejb.SessionSynchronization interface

......

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responsibility

Implement container callbacks defined inImplement container callbacks defined injavax.ejb.EntityBeanjavax.ejb.EntityBean interfaces for entitiesinterfaces for entities

Avoid programming practices that interfere with containersAvoid programming practices that interfere with containers

runtime management of bean instancesruntime management of bean instances

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Ejb-jar file

Standard format used by EJB tools for packagingStandard format used by EJB tools for packaging(assembling) beans along with declarative information(assembling) beans along with declarative information

Contract between bean provider and application assembler,Contract between bean provider and application assembler,

and between application assembler and application deployerand between application assembler and application deployer

The file includes:The file includes:

Java class files of the beans along with their remote and home

interfaces

XML deployment descriptor that provides both structural and

application assembly information about the beans

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Finally, the Big Picture

Application

ServerEJB

Container

Databases

/Other

EnterpriseSystems

HTML/Java

Client

Create, find,

remove methods

Create, find,

remove methods

Business methodsBusiness methods

Bean

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Bean Varieties

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Three Types of BeansSession Beans - Short lived and last during a sessionSession Beans - Short lived and last during a session

Entity Beans - Long lived and persist throughoutEntity Beans - Long lived and persist throughout

Message Driven Beans Asynchronous Message ConsumersMessage Driven Beans Asynchronous Message Consumers

Session A Session C

Session B

Session D

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Session Beans

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What is a Session Bean?

A session object is a non-persistent object that implements someA session object is a non-persistent object that implements somebusiness logic running on the server.business logic running on the server.

Executes on behalf of a single client.Executes on behalf of a single client.

Can be transaction aware.Can be transaction aware.

Does not represent directly shared data in the database, although it mayDoes not represent directly shared data in the database, although it mayaccess and update such data.access and update such data.

Is relatively short-lived.Is relatively short-lived.

Is removed when the EJB container crashes. The client has to re-Is removed when the EJB container crashes. The client has to re-

establish a new session object to continue computationestablish a new session object to continue computation

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Types of Session Beans

There are two types of session beans:There are two types of session beans: Stateless

Stateful

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Clients view of a Session Bean

A client accesses a session object through the session beansA client accesses a session object through the session beansRemote Interface or Local Interface.Remote Interface or Local Interface.

Each session object has an identity which, in general, doesEach session object has an identity which, in general, does

not survive a crashnot survive a crash

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Locating a session beans home interface

Remote Home interfaceRemote Home interfaceContext initialContext = new InitialContext();Context initialContext = new InitialContext();

CartHome cartHome = (CartHome)CartHome cartHome = (CartHome)

javax.rmi.PortableRemoteObject.narrow(initialContext.lookup(java:comp/env/javax.rmi.PortableRemoteObject.narrow(initialContext.lookup(java:comp/env/

ejb/cart), CartHome.class);ejb/cart), CartHome.class);

Local Home InterfaceLocal Home Interface

Context initialContext = new InitialContext();Context initialContext = new InitialContext();

CartHome cartHome = (CartHome)CartHome cartHome = (CartHome)

initialContext.lookup(java:comp/env/ejb/cart);initialContext.lookup(java:comp/env/ejb/cart);

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Session Beans Local Home Interface

object that implements is called a session EJBLocalHomeobject that implements is called a session EJBLocalHomeobject.object.

Create a new session object.Create a new session object.

Remove a session object.Remove a session object.

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Session Beans Remote Home Interface

object that implements is called a session EJBHome object.object that implements is called a session EJBHome object.

Create a session objectCreate a session object

Remove a session objectRemove a session object

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Session Beans Local Interface

Instances of a session beans remote interface are calledInstances of a session beans remote interface are calledsessionsession EJBObjecEJBObjectsts

business logic methods of the object.business logic methods of the object.

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Session Beans Local Home Interface

instances of a session beans local interface are calledinstances of a session beans local interface are calledsessionsession EJBLocalObjectEJBLocalObjectss

business logic methods of the objectbusiness logic methods of the object

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EJBObject or EJBLocalObject

Client never directly accesses instances of a Session BeansClient never directly accesses instances of a Session Beansclassclass

Client uses Session Beans Remote Interface or RemoteClient uses Session Beans Remote Interface or Remote

Home Interface to access its instanceHome Interface to access its instance

The class that implements the Session Beans RemoteThe class that implements the Session Beans Remote

Interface or Remote Home Interface is provided by theInterface or Remote Home Interface is provided by the

container.container.

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Session Object Identity

Session Objects are meant to be private resources of theSession Objects are meant to be private resources of theclient that created themclient that created them

Session Objects, from the clients perspective, appearSession Objects, from the clients perspective, appear

anonymousanonymous

Session Beans Home Interface must not define finderSession Beans Home Interface must not define finder

methodsmethods

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Session Object Identity

Stateful Session BeansStateful Session Beans

A stateful session object has a unique identity that is assigned by the

container at the time of creation

A client can determine if two object references refer to the same session

object by invoking the isIdentical(EJBObject otherEJBObject) method onone of the references

Stateless Session BeansStateless Session Beans

All session objects of the same stateless session bean, within the same home

have the same object identity assigned by the container

isIdentical(EJBObject otherEJBObject) method always returns true

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LifeCycle of a Session Object

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Activation and Passivation

Session bean container may temporarily transfer state of anSession bean container may temporarily transfer state of anidle stateful session bean instance to some form ofidle stateful session bean instance to some form of

secondary storagesecondary storage

Transfer from working set to secondary storage is calledTransfer from working set to secondary storage is called

instance passivationinstance passivation

Transfer back from the secondary storage to the instanceTransfer back from the secondary storage to the instance

variables is calledvariables is called instance activationinstance activation

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Stateless Session Bean State Diagram

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Stateful Session Bean State Diagram

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Entity Beans

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Long Live Entity Beans!

A component that represents an object-oriented view of some entitiesA component that represents an object-oriented view of some entitiesstored in a persistent storage like a database or an enterprise application.stored in a persistent storage like a database or an enterprise application.

From its creation until its destruction, an entity object lives in aFrom its creation until its destruction, an entity object lives in a

container.container.

Transparent to the client, the Container provides security, concurrency,Transparent to the client, the Container provides security, concurrency,

transactions, persistence, and other services to support the Entity Beanstransactions, persistence, and other services to support the Entity Beans

functioningfunctioning

Container Managed Persistence versus Bean Managed Persistence

Multiple clients can access an entity object concurrentlyMultiple clients can access an entity object concurrently

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...Entity Beans!

Container hosting the Entity Bean synchronizes access toContainer hosting the Entity Bean synchronizes access tothe entity objects state using transactionsthe entity objects state using transactions

Each entity object has an identity which usually survives aEach entity object has an identity which usually survives atransaction crashtransaction crash

Object identity is implemented by the container with helpObject identity is implemented by the container with helpfrom the enterprise bean classfrom the enterprise bean class

Multiple enterprise beans can be deployed in a ContainerMultiple enterprise beans can be deployed in a Container

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Remote Clients

Accesses an entity bean through the entity beans remoteAccesses an entity bean through the entity beans remoteand remote home interfacesand remote home interfaces

Implements EJBObject and EJBHome InterfacesImplements EJBObject and EJBHome Interfaces

Location IndependentLocation Independent

Potentially Expensive, Network LatencyPotentially Expensive, Network Latency

Useful for coarse grained component accessUseful for coarse grained component access

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Local Clients

Local client is a client that is collocated with the entity beanLocal client is a client that is collocated with the entity beanand which may be tightly coupled to the bean.and which may be tightly coupled to the bean.

Implements EJBLocalObject and EJBLocalHome InterfacesImplements EJBLocalObject and EJBLocalHome Interfaces

Same JVMSame JVM

Enterprise bean can-not be deployed on a node differentEnterprise bean can-not be deployed on a node different

from that of its client - Restricts distribution of components.from that of its client - Restricts distribution of components.

Better supports fine-grained component accessBetter supports fine-grained component access

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Entity Beans Remote Home Interface

Container provides the implementation of the RemoteContainer provides the implementation of the RemoteHome Interface for each Entity Bean deployed in theHome Interface for each Entity Bean deployed in the

containercontainer

Container makes the Remote Home Interface of all EntityContainer makes the Remote Home Interface of all Entity

Beans deployed in it accessible to Clients through JNDIBeans deployed in it accessible to Clients through JNDI

The object that implements an Entity Beans Remote HomeThe object that implements an Entity Beans Remote Home

Interface is called anInterface is called anEJBHomeEJBHome objectobject

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Entity Beans Remote Home Interface

Create new entity objects within the homeCreate new entity objects within the home

Find existing entity objects within the homeFind existing entity objects within the home

Remove an entity object from the homeRemove an entity object from the home

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Create Methods

Entity Beans Remote Home Interface can define multipleEntity Beans Remote Home Interface can define multiple

create()create()

methods, each defining a way of creating an entity objectmethods, each defining a way of creating an entity object

Arguments ofArguments ofcreate()create() initialize the state of the entity objectinitialize the state of the entity object

Return type of aReturn type of a create()create() method is Entity Beans Remote Interfacemethod is Entity Beans Remote Interface

TheThe throwsthrows clause of everyclause of every create()create() method includes themethod includes thejava.rmi.RemoteExceptionjava.rmi.RemoteException andandjavax.ejb.CreateExceptionjavax.ejb.CreateException

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finderMethods

Entity Beans Home Interface defines manyEntity Beans Home Interface defines many

finderfinder

methodsmethods

Name of eachName of each finderfindermethod starts with the prefix findmethod starts with the prefix find

Arguments of aArguments of afinderfindermethod are used by the Entity Beanmethod are used by the Entity Bean

implementation to locate requested entity objectsimplementation to locate requested entity objects

Return type of aReturn type of afinderfindermethod must be the Entity Beans Remotemethod must be the Entity Beans RemoteInterface, or a collection of Remote InterfacesInterface, or a collection of Remote Interfaces

TheThe throwsthrows clause of everyclause of everyfinderfindermethod includes themethod includes the

java.rmi.RemoteExceptionjava.rmi.RemoteException andandjavax.ejb.FinderExceptionjavax.ejb.FinderException

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Entity Beans Remote Interface

Client accesses an entity object through Entity Beans Remote InterfaceClient accesses an entity object through Entity Beans Remote Interface

Entity beans Remote Interface must extendEntity beans Remote Interface must extendjavax.ejb.EJBObjectjavax.ejb.EJBObject

interfaceinterface

Remote Interface defines business methods which are callable by clientsRemote Interface defines business methods which are callable by clients

The container provides the implementation of the methods defined inThe container provides the implementation of the methods defined inthethejavax.ejb.EJBObjectjavax.ejb.EJBObjectinterfaceinterface

Only business methods are delegated to the instances of the enterpriseOnly business methods are delegated to the instances of the enterprise

bean classbean class

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Entity Objects Life Cycle

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Entity Beans Local Home Interface

must extend themust extend the javax.ejb.EJBLocalHomejavax.ejb.EJBLocalHome interfaceinterface Each method must be one of the:Each method must be one of the:

Create methods

Find methods

Home methods

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Entity Beans Local Interface

Local client can access an entity object through the entity beans localLocal client can access an entity object through the entity beans local

interface.interface.

must extend themust extend the javax.ejb.EJBLocalObjectjavax.ejb.EJBLocalObject interface.interface.

defines the business methods callable by local clients.defines the business methods callable by local clients.

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Persistence Management

Data access protocol for transferring state of the entityData access protocol for transferring state of the entitybetween the Entity Bean instances and the database isbetween the Entity Bean instances and the database isreferred to as object persistencereferred to as object persistence

There are two ways to manage this persistence during anThere are two ways to manage this persistence during anapplications lifetimeapplications lifetime

Bean-managed

Container-managed

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Bean Managed Persistence

Entity Bean provider writes database access calls directlyEntity Bean provider writes database access calls directlyinto the enterprise bean classinto the enterprise bean class

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Container Managed Persistence

Bean Provider need not write database calls in the beanBean Provider need not write database calls in the bean

Container providers tools generate database access calls atContainer providers tools generate database access calls atdeployment timedeployment time

Advantage:Advantage: Entity Bean can be mostly independent fromEntity Bean can be mostly independent from

the data source in which the entity is storedthe data source in which the entity is stored Disadvantage:Disadvantage: Sophisticated tools are needed atSophisticated tools are needed at

deployment time to map Entity Bean fields to data sourcedeployment time to map Entity Bean fields to data source

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Life Cycle of an Entity Bean Instance

Q

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EJB QL

Need for standardizing queriesNeed for standardizing queries Why not SQL?Why not SQL?

EJB QL: EJB Query LanguageEJB QL: EJB Query Language

Specification language Based on the CMP Data Model (Abstract Persistence Schema)

Compiled to a target language: SQL

EJB QL E l

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EJB QL Example

SELECT OBJECT(l) From OrderBean o, in(o.lineItems) lSELECT OBJECT(l) From OrderBean o, in(o.lineItems) l

SELECT l.LINEITEM_ID FROM LINEITEMEJBTABLE l, ORDEREJBTABLE oSELECT l.LINEITEM_ID FROM LINEITEMEJBTABLE l, ORDEREJBTABLE o

WHERE (l.ORDER_ID = o.ORDER_ID )WHERE (l.ORDER_ID = o.ORDER_ID )

SELECT OBJECT(o) FROM OrderBean o WHERE o.creditCard.expires = '03/05'"SELECT OBJECT(o) FROM OrderBean o WHERE o.creditCard.expires = '03/05'"

SELECT o.ORDER_ID FROM CREDITCARDEJBTABLE a_1,SELECT o.ORDER_ID FROM CREDITCARDEJBTABLE a_1,

ORDEREJBTABLE o WHERE ((a_1.EXPIRES='03/05' ANDORDEREJBTABLE o WHERE ((a_1.EXPIRES='03/05' AND

o.CREDITCARD_ID = a_1.CREDITCARD_ID ))o.CREDITCARD_ID = a_1.CREDITCARD_ID ))

EJB QL E l

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EJB QL Example

SELECT c.addressSELECT c.address

FROM CustomerBeanSchema cFROM CustomerBeanSchema c

WHERE c.iD=?1 AND c.firstName=?2WHERE c.iD=?1 AND c.firstName=?2

SELECT ADDRESS.IDSELECT ADDRESS.ID

FROM ADDRESS, CUSTOMERFROM ADDRESS, CUSTOMER

WHERE CUSTOMER.CUSTOMERID=?WHERE CUSTOMER.CUSTOMERID=?

AND CUSTOMER.FIRSTNAME=?AND CUSTOMER.FIRSTNAME=?

AND CUSTOMER.CUSTOMERID = ADDRESS.CUSTOMERIDAND CUSTOMER.CUSTOMERID = ADDRESS.CUSTOMERID

EJB QL D l D i

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EJB QL: Deployment Descriptor

Method finds large ordersMethod finds large orders

findAllCustomersfindAllCustomers

SELECT OBJECT(c) FROM CustomerBeanSchema cSELECT OBJECT(c) FROM CustomerBeanSchema c

H B i M h d

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Home Business Methods

Methods in the Home InterfaceMethods in the Home Interface

Implementation provided by Bean Provider with matchingImplementation provided by Bean Provider with matching

ejbHomeejbHome in the Beanin the Bean

Exposed to the Client ViewExposed to the Client View

Not specific to any Bean instanceNot specific to any Bean instance

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E l f EJB 2 0 CMP B

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Example of EJB 2.0 CMP Bean

publicpublic abstractabstract class AccountBean implements EntityBean {class AccountBean implements EntityBean {

////Virtual FieldsVirtual Fields

publicpublic abstractabstract long getAccount_number();long getAccount_number();

publicpublic abstractabstract void setAccount_number(long account_number);void setAccount_number(long account_number);

publicpublic abstractabstract java.lang.String getCustomer_name();java.lang.String getCustomer_name();

publicpublic abstractabstract void setCustomer_name(String customer_name);void setCustomer_name(String customer_name);

publicpublic abstractabstract double getBalance();double getBalance();

publicpublic abstractabstract void setBalance(double balance);void setBalance(double balance);

// Business Method// Business Method

public void credit ( double amount ) {public void credit ( double amount ) {

double balance =double balance = getBalance();getBalance();

balance += amount;balance += amount;

setBalance(balance);setBalance(balance);

}}

}}

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Abstract Schema : Deployment Descriptor

CustomerBeanSchemaCustomerBeanSchema

id of the customerid of the customer

iDiD

First name of the customerFirst name of the customer

firstNamefirstName

Last name of the customerLast name of the customer

lastNamelastName

iDiD

C t i M d R l ti hi

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Container Managed Relationships

Container Managed RelationshipsContainer Managed Relationships

Bean-Bean, Bean-Dependent, Dependent-DependentBean-Bean, Bean-Dependent, Dependent-Dependent

Defined using Abstract Accessor MethodsDefined using Abstract Accessor Methods

Unidirectional or Bi-directionalUnidirectional or Bi-directional

LineItem Product

Student Course

CardinalityCardinality

One to One

One to Many

Many to One

Many to Many

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E l E tit B P d t

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Example Entity Bean: Product

public abstract OrderBean extends Entity Bean {public abstract OrderBean extends Entity Bean {

// Virtual Fields // Virtual Fields

public abstract Long getProductID();public abstract Long getProductID();

public abstract void setProductID(Long orderID);public abstract void setProductID(Long orderID);

// Virtual Fields // Virtual Fields

public abstract String getProductCategory();public abstract String getProductCategory();

public abstract void setProductCategory (String category);public abstract void setProductCategory (String category);

// NO Relationship Fields// NO Relationship Fields

}}

Relationships: Deployment Descriptor

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Relationships: Deployment Descriptor

ONE-TO-ONE: Customer and AddressONE-TO-ONE: Customer and Address

Customer-AddressCustomer-Address

customer has one addresss customer has one addresss

oneone

CustomerBeanCustomerBean

addressaddress

Address belong to the Customer Address belong to the Customer

oneone

AddressBeanAddressBean

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MDB: Whats the need ?

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MDB: Whats the need ?

Interactions between client and Home, Remote Interfaces ofInteractions between client and Home, Remote Interfaces of

session and entity beans is synchronoussession and entity beans is synchronous

Request sentRequest sent Server Object respondsServer Object responds

Leads to blockage till response occursLeads to blockage till response occurs

EJB model does not allow creation of threads withinEJB model does not allow creation of threads within

component codecomponent code

Message Driven Beans (MDB)

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Message Driven Beans (MDB)

Asynchronous message consumer.Asynchronous message consumer.

Can consume messages from Topics and QueuesCan consume messages from Topics and Queues

Invoked by the container on the arrival of a JMS message.Invoked by the container on the arrival of a JMS message.

No conversational state. - all bean instances are equivalentNo conversational state. - all bean instances are equivalent

when they are not involved in servicing a client message.when they are not involved in servicing a client message.

Anonymous - No client-visible identityAnonymous - No client-visible identity

No Home, Remote Interface - Not exposed to client viewNo Home, Remote Interface - Not exposed to client view


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GoalGoal Make developing an enterprise bean that is asynchronouslyMake developing an enterprise bean that is asynchronously

invoked to handle the processing of incoming JMSinvoked to handle the processing of incoming JMS

messages as simple as developing the same functionality inmessages as simple as developing the same functionality in

any other JMS MessageListener.any other JMS MessageListener. To allow for the concurrent processing of a stream ofTo allow for the concurrent processing of a stream of

messages by means of container-provided pooling ofmessages by means of container-provided pooling of

message-driven bean instances.message-driven bean instances.

Client View of MDBs

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Client View of MDBs

The existence of a message-driven bean is completelyThe existence of a message-driven bean is completelyhidden behind the JMS destination for which the MDB ishidden behind the JMS destination for which the MDB is

the message listener.the message listener.

MethodMethod onMessageonMessage triggered by an incoming messagetriggered by an incoming message

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Responsibilities

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Responsibilities

Bean ProviderBean Provider

Provide MDB class

ejbCreate()

onMessage()

ejbRemove()

Container ProviderContainer Provider

Generation of implementation classes

Deployment of MDBs

Transactions, security

E l MDB A li ti

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Example MDB Application

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m4_ejb

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