ejb lecture

8/13/2019 EJB Lecture

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Page 1, 5-Nov-03Component Technologies

EJB

Enterprise Java BeansEnterprise Java Beans

Mikael kerholm


EJB

LectureLecture StuctureStucture

Introduction1. Java

2. JavaBeans

3. J2EE

J2EE1. EJB

2. Java Serverlets, JSP, and clients

3. Packaging and Deployment

Summary, Questions


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EJB

ReferencesReferences

Literature:Enterprise JavaBeans, R.M. Haefel, 3rd OReilly 2001

The Source for Java Technology, good, up to date,tutorials, specifications, and reference implementations

http://java.sun.com/


EJB

JavaJava

The current main release is the Java 2 platform, it ismodular and include three parts:

J2SE, Java 2 Platform, Standard Editionprovides the essential compiler, tools, runtimes, and APIs for writing,deploying, and running applets and applications

J2EE, Java 2 Platform, Enterprise Editioncomponent based model, simplifies enterprise development anddeployment; manages the infrastructure and supports the web services toenable development business applications

J2ME, Java 2 Platform, Micro Editiona highly optimized Java runtime environment, specifically addresses thevast consumer space (embedded systems), from smart cards to more PClike applications


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EJB

Java 2 Enterprise Edition (J2EE)Java 2 Enterprise Edition (J2EE)

For enterprise applications (distributed businessapplications)

Demands Availability

Security

Reliability

Scalability

From the early 90sShift from 2-tier, client-server application models to more flexible 3-tier (and n-tier)application models

The new models separated business logic from system services and the user interface


EJB


DatabaseDatabase

Tier Boundary

Business

logic

Business

logic

Databasedriver

Databasedriver

Business

logic

Business

logic

PresentationPresentation

Data tier

Business tier

Tier Boundary

Presentation tier


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EJB



EJB


J2EE Application Programming Model Applications on the client

Java Server Pages (JSP), web components on the server,extension of Serverlets; in the end these are concerned withclients

EJB, business components on the server side


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EJB

EnterpriseEnterprise JavaBeanJavaBean (EJB)(EJB)

Javas component model for distributed enterpriseapplications, released 1998

EJB technology defines a model for the development ofreusable Java server componentsDef:

Enterprise Java Beans is a standard server-side componentfor computer transaction monitors.

Applications written using EJB are:Scalable

Transactional

Multi-User secure


EJB

EJB != JBEJB != JB

Once and for allJB

Desktop Components

EJBEnterprise Distributed Components

Could of course be implemented using JavaBeans


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EJB

J2EEJ2EE


EJB

ContentsContents

1. EJB ComponentsGeneral

Interfaces and classes

Architechture

Different types

Transactions

2. Java Serverlets, JSP and clientsBrief

3. Packaging and DeploymentBrief


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EJB

What is an EnterpriseWhat is an Enterprise JavaBeanJavaBean ??

A server-side component thatencapsulates the business logic of anapplication


EJB

When to use Enterprise JavaBeansWhen to use Enterprise JavaBeans

If any of these requirements hold for yourapplication:

The application must be scalable anddistributable

Transactions are required to ensure dataintegrity

The application will have a variety of clients


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EJB

Enterprise JavaBeansEnterprise JavaBeans

Entity Beans

Persistent

Primary key

Session Beans

Receive their state from the client

Live as long as the client need them

Message-Driven Beans (EJB 2.0)

Asynchronously

Only a bean class no interfaces


EJB

Classes and InterfacesClasses and Interfaces

Remote Interface

Specifies the beans business methods

Home Interface

Defines the beans life cycle methods

Bean Class

Implements the beans business methods

Primary Key

Provides a pointer into the database


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EJB

A Beans interfacesA Beans interfaces

Remote InterfaceBusiness methods to do the beans work

Implemented by the shadowdy Bean Object

Remote Home InterfaceDefines the beans life cycle methods

Implemented by EJB Home

Local Interface (EJB 2.0)Business methods used by other beans in the samecontainer

Local Home Interface (EJB 2.0)Life-cycle methods used by other beans in the samecontainer


EJB

A Beans classesA Beans classes

The Bean ClassImplement the business methods

Do not implement Remote (or local) and (local) HomeInterfaces

Beans exist in the middle of client software and datasources

Clients never interact directly with the bean class, usesmethods of the Remote and Home Interface, interactingwith automatically generated stubs


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EJB

EJB ArchitectureEJB Architecture

HomeObjectHomeObject

EJB Server

BeanClassBeanClass

EJB Container

EJB Client

EJBObjectEJB

Object

Home InterfaceHome Interface

Remote InterfaceRemote Interface

(or Local Interface)(or Local Interface)

HomeStub

HomeStub

ObjectStub

ObjectStub


EJB

When to use Entity BeansWhen to use Entity Beans

The bean represents a business entity, not aprocedure

To provide a safe and consistent interface to a set ofshared data


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EJB

Entity BeansEntity Beans

Represents a business object in a persistentstorage mechanism

Can be shared by multiple clients

Two types of persistence:

Container-managed

Bean-managed


EJB

Container Container --managed persistencemanaged persistence

They are the simplest to develop

The beans code contain no database accesscalls


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EJB

BeanBean --managed persistencemanaged persistence

Explicitly write persistence logic

More flexibility in how state is managed betweenthe bean instance and the database

Used when deployment tools are inadequate


EJB

Life CycleLife Cycle


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EJB

When to use Session BeansWhen to use Session Beans

Only one client has access to the beans instance

Non persistent and existing only for a short period oftime


EJB

Session BeansSession Beans

Useful for describing interactions

Does not represent shared data in the database,but can access shared data

Two types:Stateless

Stateful


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EJB

Stateless Session BeansStateless Session Beans

Supports multiple clients

Relatively easy to develop and very efficient

Require few server resources

Stateless session beans are appropriate if:

The bean's state has no data for a specific client

A generic task is performed in a single methodinvocation

The bean fetches a set of read-only data


EJB



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EJB

StatefulStateful Session BeansSession Beans

Dedicated to one client for the life of the beaninstance

Instance variables represent the state of a uniqueclient-bean session

Stateful session beans are appropriate if:

The bean needs to hold information about theclient across method invocations

The bean mediates between the client and theother components of the application


EJB



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EJB

When to use MessageWhen to use Message --Driven BeansDriven Beans

To receive messages asynchronously

When consuming JMS messages


EJB

MessageMessage --Driven BeansDriven Beans

Has only a bean class

Can consume and process messagesconcurrently

Acts as a JMS message listener Deliver messages to a virtual channel

Currently process only JMS messages


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EJB



EJB

Calling an EJBCalling an EJB

HomeObjectHomeObject

EJB Server

BeanClassBeanClass

EJB Container

EJBObjectEJB

Object

4 Create EJB Object

7 Wraps the call to the Bean Class

EJB Client

1 Ask for Home object

2 Returnreferencehome stub

JNDI

3 Ask for EJB Object

5 Return Obj stub

6 Invoke a method


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EJB

Transactions withTransactions with EJBsEJBs

Managed automatically

No use of APIDefined at deployment

Possible to explicitly manage transactions but notrecommended


EJB

A TransactionA Transaction

Transactions is the execution of a unit-of-work thataccesses on or more resources, usually databasesA unit-of-work is a set of activities that relate to eachother and must be completed together

The objective with transactions is to execute an unit-ofwork that results in a reliable exchangeTransactions are often complex and usually involvemanipulation of dataTransactions must work perfectly every time or not beexecuted at all


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EJB

AcidAcid--propertiesproperties

Atomic A transaction must execute completely or not at all

Consistent A transaction always leads to a correct transformation ofthe system state by preserving the state invariance

IsolatedThe data a transaction access cannot be affected by anyother parts of the system until the transaction iscompleted

Durable All the data changes made during the course of

transaction must be written to a physical storage beforethe transactions is physically completed


EJB

Transaction ManagementTransaction Management

Declarative transaction managementThe transactional behavior controls by usingtransactions attribute in the deployment descriptor

One of the primary advantages of EJB

Reduce the complexity for the developers

Makes it easier to create robust transaction applications

Explicit transaction managementDifficult to use

Will not be covered in this talk


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EJB

Transactions AttributeTransactions Attribute You can set the runtime transaction attribute as a XML-attribute in the deployment descriptor by hand, but wewill use a deployment wizardIt is more efficient and easier to use transactionattributes than to control transactions explicitlyIt is possible to set a transaction attribute for the entirebean or to set different transactions attribute forindividual methodsThere exist six transaction attributes in EJB 2.0:

NotSupported

Supports

Required

RequiresNewMandatory

Never


EJB

The Different Transactions AttributesThe Different Transactions Attributes

NotSupportedInvoking a method on a bean with this transactionattribute suspends the transactions until the method iscompleted

SupportsMeans that the bean method will be included in thetransactions scope if it is invoked within a transaction

RequiredMeans that the bean method must be invoked within thescope of a transaction


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EJB

The Different Attributes, Cont.The Different Attributes, Cont.

RequiresNewMeans that a new transactions always starts

MandatoryMeans that the bean method must always be made partof the transaction scope of the calling client

Never Means that the bean method must never be invokedwithin the scope of a transaction


EJB

JavaJava ServerletsServerlets , JSP and clients, JSP and clients


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EJB

ServerletsServerlets

A serverlet is a server side component, which isdeployed in the same fashion as a EJB

Used to dynamically create html pages, for clientsSince it is server side, it extends the reach for clients tobackend components (e.g., EJBs) in the server

A servelet is assigned to handle an access for a specifichtml page

When the specific page is requsted by a browser, amethod in the servelet is envoked which posts the htmlpage back

When a client looks at the html code posted from theserver, it looks just like a static html page


EJB

JavaServer JavaServer Pages, JSPPages, JSP

An extension of serverlets, simplifies the creation ofdynamic htmlSimply lets the developer incorporate real java code intoa html page when desired (as a scripting language)

Is actually compiled to servelets


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EJB

ClientsClients

Web clients with serverlets or JSP, JSP possibly morepowerful

Can also create application clients An client side component, that access EJBs

Easy and straightforward to create, deploted in the samefashion as EJBs


EJB

Packaging and DeploymentPackaging and Deployment


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EJB

Deployment and Deploy ToolsDeployment and Deploy Tools

PackagingCreate JAR files

A compressed platform-independent file

Bean and Beans interface and help classes

Create deployment descriptorsXML files specifying

Access control

Bean references

External Resource references

Transactional attributes

DeploymentDeploy the application on a server


EJB

PackagingPackaging andand DeploymentDeployment

Can be done by handGives full control

Time consuming

Graphical deplytool with wizards included in thereference implementation

Easy, fast


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EJB

SummarySummary

JB != EJBEJBs Typically used for 3 or more tiers bussinessapplicationsEJBs, server side components, with remote and homeinterfaces; packaged in JAR files with deploymentdescriptors

Session, Entity, Message

Clients, can be applications or web pages throughservelets or JSP


EJB

ExampleExample

Entity Bean PersonEntity Bean PersonLets look how to build a bean


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EJB

The Remote InterfaceThe Remote Interface

/**/**Remote InterfaceRemote InterfaceBusiness methods for Person beansBusiness methods for Person beans

*/*/

importimport javax.ejb.Exceptionjavax.ejb.Exception ;;

public interface Person extendspublic interface Person extends javax.ejb.EJBObjectjavax.ejb.EJBObject {{StringString getNamegetName () throws() throws RemoteExceptionRemoteException ;;voidvoid setName(StringsetName(String n) throwsn) throws RemoteExceptionRemoteException ;;

}}


EJB

The Home InterfaceThe Home Interface

/**/**Home InterfaceHome InterfaceLife cycle method for Person beansLife cycle method for Person beans*/*/

importimport java.rmi.RemoteExceptionjava.rmi.RemoteException ;;importimport javax.ejb.CreateExceptionjavax.ejb.CreateException ;;importimport javax.ejb.FinderExceptionjavax.ejb.FinderException ;;

public interfacepublic interface PersonHomePersonHome extendsextends javax.ejb.EJBHomejavax.ejb.EJBHome {{

//responsible for//responsible for initalizinginitalizing an instance of the beanan instance of the beanpublic Personpublic Person create(intcreate(int id)id)

throwsthrows CreateExceptionCreateException ,, RemoteExceptionRemoteException ;;

//look up a bean in a DB//look up a bean in a DBpublicpublic findByPK(PersonPKfindByPK(PersonPK pkpk ))

throwsthrows FinderExceptionFinderException ,, RemoteExceptionRemoteException ;;}}


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EJB

The Bean ClassThe Bean Class/**/**Bean ClassBean ClassImplements the business methods for Person componentImplements the business methods for Person componentPerson Bean is a Entity BeanPerson Bean is a Entity Bean*/*/public classpublic class PersonBeanPersonBean implementsimplements javax.ejb.EntityBeanjavax.ejb.EntityBean {{

privateprivate intint id;id;private String name;private String name;

//business methods//business methodspublic Stingpublic Sting getNamegetName () {() {

return name;return name;}}

public voidpublic void setName(StringsetName(String n) {n) {name=n;name=n;

}}

// continue next slide// continue next slide


EJB

// and the bean class continues// and the bean class continues//// ejb.entityejb.entity methodsmethods

publicpublic PersonPKPersonPK ejbCreate(intejbCreate(int i) {i) {id=i;id=i;return null;return null;

}}

public voidpublic void ejbPostCreate(intejbPostCreate(int i) {/*+*/}i) {/*+*/}public voidpublic void ejbSetEntityContext(EntityContextejbSetEntityContext(EntityContext ctxctx ) {}) {}public voidpublic void ejbUnsetEntityContextejbUnsetEntityContext () {/*+*/}() {/*+*/}public voidpublic void ejbActivateejbActivate () {}() {}public voidpublic void ejbPassivateejbPassivate () {}() {}public voidpublic void ejbLoadejbLoad () {/*+*/}() {/*+*/}public voidpublic void ejbStoreejbStore () {/*+*/}() {/*+*/}public voidpublic void ejbRemoveejbRemove () {}() {}

// + note: session beans do not have these methods// + note: session beans do not have these methods}}


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EJB

ExampleExampleSimple JSP pageSimple JSP page

How to build a web client


EJB


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EJB

publicpublic voidvoid jspDestroyjspDestroy () {() {converterconverter == nullnull ;;

}}%>%>

0 ) {

BigDecimalBigDecimal d = newd = new BigDecimalBigDecimal (( amountamount ););%>%>

Euro.Euro.


EJB

ExampleExample

A deployment descriptor A deployment descriptor Good to understand, when time allows!


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EJB

XML Document Header XML Document Header

XML documents start with two general information tags:

1. Specifies the XML version the file use

2. Specifies the DTD that defines the XML fileProvides the URL to the DTD, you can download it andvalidate the XML file


EJB

XML Descriptors BodyXML Descriptors Body

The Body start with a root element defined by the DTD.The root element describing:

Bean/ Beans Entity or Session Beans

Primary KeyEnvironment Entries

Reference to other Beans

Reference to External Resources (such as a Database)

Security Roles

Bean/Beans Assembly Transactional attributes

Security roles & Method permissions


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EJB

XML Body exampleXML Body example

a body examplea body example

-- -- --

-- -- --

-- -- --

-- -- --


EJB

a Bean example a Bean example PlayerBeanPlayerBean com.chess.player.PlayerHomecom.chess.player.PlayerHome com.chess.player.Playercom.chess.player.Player com.chess.player.PlayerBeancom.chess.player.PlayerBean

ididfield>FalseFalseididfield>

-- -- --namenamefield>

XML Bean exampleXML Bean example


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EJB

...

allows to read/writeeveryone

everyone

myBean*

XMLXMLSecurity Roles and Method permissionsSecurity Roles and Method permissions

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