Enterprise Java Beans - idt.mdh.se Page 1, 5-Nov-03 Component Technologies EJB Enterprise Java Beans Mikael Åkerholm Page 2, 5-Nov-03 Component Technologies EJB Lecture Stucture Introduction

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Page 1, 5-Nov-03Component Technologies

EJB

Enterprise Java BeansEnterprise Java Beans

Mikael Åkerholm


EJB

Lecture Lecture StuctureStucture

Introduction1. Java2. JavaBeans3. J2EE

J2EE1. EJB2. Java Serverlets, JSP, and clients3. Packaging and Deployment

Summary, Questions

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EJB

ReferencesReferences

Literature:Enterprise JavaBeans, R.M. Haefel, 3rd O’Reilly 2001

The Source for Java Technology, good, up to date, tutorials, specifications, and reference implementationshttp://java.sun.com/


EJB

JavaJava

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

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

J2EE, Java 2 Platform, Enterprise Edition component based model, simplifies enterprise development and deployment; manages the infrastructure and supports the web services to enable development business applications

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

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EJB

JavaBeansJavaBeans

A desktop component model for Java, included among the J2SE technologies

A Java API and a Specification

Software reuse for Software Development

Object-Oriented

Focus on lightweight components for small-scale CBD


EJB

JavaBeansJavaBeans

Use standard naming conventionsHave public interfacesPackaged in JAR filesInterface composed of:

Properties:Simple, Boolean or IndexedCould be Bound or Constrained

Events:signaled by changing propertiessignaled for custom state changes

Methods:default is any public methodBuilt via BeanInfo class or Reflection API

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EJB

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

For enterprise applications (distributed business applications)

DemandsAvailabilitySecurityReliabilityScalability

From the early 90sShift from 2-tier, client-server application models to more flexible 3-tier (and n-tier) application modelsThe new models separated business logic from system services and the user interface


EJB


DatabaseDatabase

Tier Boundary

Businesslogic

Businesslogic

Databasedriver

Databasedriver

Businesslogic

Businesslogic

PresentationPresentation

Data tier

Business tier

Tier Boundary

Presentation tier

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EJB



EJB


J2EE Application Programming ModelApplications on the clientJava Server Pages (JSP), web components on the server, extension of Serverlets; in the end these are concerned with clients EJB, business components on the server side

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EJB

Enterprise Enterprise JavaBeanJavaBean (EJB)(EJB)

Java’s component model for distributed enterprise applications, released 1998EJB technology defines a model for the development of reusable Java server componentsDef:

”Enterprise Java Beans is a standard server-side component for computer transaction monitors.”Applications written using EJB are:

ScalableTransactionalMulti-User secure


EJB

EJB != JBEJB != JB

Once and for allJB

Desktop ComponentsEJB

Enterprise Distributed ComponentsCould of course be implemented using JavaBeans

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EJB

J2EEJ2EE


EJB

ContentsContents

1. EJB ComponentsGeneralInterfaces and classesArchitechtureDifferent typesTransactions

2. Java Serverlets, JSP and clientsBrief

3. Packaging and DeploymentBrief

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EJB

What is an Enterprise What is an Enterprise JavaBeanJavaBean??

”A server-side component that encapsulates the business logic of an application”


EJB

When to use Enterprise JavaBeansWhen to use Enterprise JavaBeans

If any of these requirements hold for your application:

The application must be scalable and distributable

Transactions are required to ensure data integrity

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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A Bean’s interfacesA Bean’s interfaces

Remote InterfaceBusiness methods to do the beans workImplemented by the “shadowdy” Bean Object

Remote Home InterfaceDefines the beans life cycle methodsImplemented by EJB Home

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

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


EJB

A Bean’s classesA Bean’s classes

The Bean ClassImplement the business methodsDo not implement Remote (or local) and (local) Home InterfacesBeans exist in the middle of client software and data sourcesClients never interact directly with the bean class, uses methods of the Remote and Home Interface, interacting with automatically generated stubs

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EJB ArchitectureEJB Architecture

HomeObjectHomeObject

EJB Server

Bean ClassBean Class

EJB Container

EJB Client

EJBObjectEJB

Object

Home InterfaceHome Interface

Remote InterfaceRemote Interface(or Local Interface)(or Local Interface)

HomeStub

HomeStub

Object Stub

Object Stub


EJB

When to use Entity BeansWhen to use Entity Beans

The bean represents a business entity, not a procedure

To provide a safe and consistent interface to a set of shared data

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EJB

Entity BeansEntity Beans

Represents a business object in a persistent storage mechanism

Can be shared by multiple clients

Two types of persistence:

Container-managed

Bean-managed


EJB

ContainerContainer--managed persistencemanaged persistence

They are the simplest to develop

The bean’s code contain no database access calls

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EJB

BeanBean--managed persistencemanaged persistence

Explicitly write persistence logic

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

Used when deployment tools are inadequate


EJB

Life CycleLife Cycle

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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 of time


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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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 method invocation

The bean fetches a set of read-only data


EJB


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StatefulStateful Session BeansSession Beans

Dedicated to one client for the life of the bean instance

Instance variables represent the state of a unique client-bean session

Stateful session beans are appropriate if:

The bean needs to hold information about the client across method invocations

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


EJB


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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 messages concurrently

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

Bean ClassBean Class

EJB Container

EJBObjectEJB

Object

4 Create EJB Object

7 Wraps the call to the Bean Class

EJB Client

1 Ask forHome object

2 Returnreferencehome stub

JNDI

3 Ask for EJB Object

5 Return Obj stub

6 Invoke a method

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EJB

Transactions with Transactions with EJBsEJBs

Managed automatically

No use of APIDefined at deployment

Possible to explicitly manage transactions but not recommended


EJB

A Transaction A Transaction

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

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

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EJB

AcidAcid--propertiesproperties

AtomicA transaction must execute completely or not at all

ConsistentA transaction always leads to a correct transformation of the system state by preserving the state invariance

IsolatedThe data a transaction access cannot be affected by any other parts of the system until the transaction is completed

DurableAll the data changes made during the course of transaction must be written to a physical storage before the transactions is physically completed


EJB

Transaction ManagementTransaction Management

Declarative transaction managementThe transactional behavior controls by using transactions attribute in the deployment descriptorOne of the primary advantages of EJBReduce the complexity for the developersMakes it easier to create robust transaction applications

Explicit transaction managementDifficult to useWill not be covered in this talk

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EJB

Transactions AttributeTransactions AttributeYou can set the runtime transaction attribute as a XML-attribute in the deployment descriptor by hand, but we will use a deployment wizardIt is more efficient and easier to use transaction attributes than to control transactions explicitlyIt is possible to set a transaction attribute for the entire bean or to set different transactions attribute for individual methodsThere exist six transaction attributes in EJB 2.0:

NotSupportedSupportsRequiredRequiresNewMandatoryNever


EJB

The Different Transactions AttributesThe Different Transactions Attributes

NotSupportedInvoking a method on a bean with this transaction attribute suspends the transactions until the method is completed

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

RequiredMeans that the bean method must be invoked within the scope 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 part of the transaction scope of the calling client

NeverMeans that the bean method must never be invoked within the scope of a transaction


EJB

Java Java ServerletsServerlets, JSP and clients, JSP and clients

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EJB

ServerletsServerlets

A serverlet is a server side component, which is deployed in the same fashion as a EJBUsed to dynamically create html pages, for clients

Since it is server side, it extends the reach for clients to backend 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, a method in the servelet is envoked which posts the html page back

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


EJB

JavaServerJavaServer Pages, JSPPages, JSP

An extension of serverlets, simplifies the creation of dynamic html Simply 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 morepowerfulCan also create application clients

An client side component, that access EJBsEasy and straightforward to create, deploted in the same fashion as EJBs


EJB

Packaging and DeploymentPackaging and Deployment

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Deployment and Deploy ToolsDeployment and Deploy Tools

PackagingCreate JAR files

A compressed platform-independent fileBean and Beans interface and help classes

Create deployment descriptorsXML files specifyingAccess controlBean referencesExternal Resource referencesTransactional attributes

DeploymentDeploy the application on a server


EJB

PackagingPackaging and and DeploymentDeployment

Can be done by handGives full controlTime consuming

Graphical deplytool with wizards included in the reference implementation

Easy, fast

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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, MessageClients, can be applications or web pages throughservelets or JSP


EJB

ExampleExampleEntity Bean PersonEntity Bean Person

“Let’s look how to build a bean”

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The Remote InterfaceThe Remote Interface

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

import import javax.ejb.Exceptionjavax.ejb.Exception;;

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

}}


EJB

The Home InterfaceThe Home Interface

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

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

public interface public interface PersonHomePersonHome extends extends javax.ejb.EJBHomejavax.ejb.EJBHome {{

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

throws throws CreateExceptionCreateException, , RemoteExceptionRemoteException;;

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

throws throws 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 class public class PersonBeanPersonBean implements implements javax.ejb.EntityBeanjavax.ejb.EntityBean {{

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

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

return name;return name;}}

public void public 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

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

}}

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

<%<%---- A A jspjsp filefile that that useuse a session a session beanbean ----%>%>

<%@ page <%@ page import="Converter,ConverterHome,javax.ejbimport="Converter,ConverterHome,javax.ejb.*, .*, java.mathjava.math.*, .*, javax.namingjavax.naming.*, .*, javax.rmi.PortableRemoteObjectjavax.rmi.PortableRemoteObject, , java.rmi.RemoteExceptionjava.rmi.RemoteException" %>" %>

<%!<%!private private ConverterConverter converterconverter = = nullnull;;

<%<%---- The The initinit methodmethod, JNDNI , JNDNI lookuplookup ----%>%>public public voidvoid jspInitjspInit() { () {

try {try {InitialContextInitialContext icic = new = new InitialContextInitialContext();();Object Object objRefobjRef = = ic.lookup("java:compic.lookup("java:comp//envenv//ejbejb//TheConverterTheConverter");");ConverterHomeConverterHome homehome = =

((ConverterHome)PortableRemoteObject.narrow(objRef,ConverterHome.cConverterHome)PortableRemoteObject.narrow(objRef,ConverterHome.classlass););

converterconverter = = home.createhome.create();();} } catchcatch ((ExceptionException ex) {ex) {

System.out.println("Couldn'tSystem.out.println("Couldn't createcreate converterconverter beanbean."+ ."+ ex.getMessageex.getMessage());());

}}

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EJB

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

}}%>%><html><html><form <form method="getmethod="get">"><input <input type="texttype="text" " name="amountname="amount" size="25">" size="25"><input <input type="submittype="submit" " value="Submitvalue="Submit"> </form>"> </form><%<%

StringString amountamount = = request.getParameter("amountrequest.getParameter("amount");");ifif ( ( amountamount != != nullnull && && amount.lengthamount.length() > 0 ) {() > 0 ) {

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

<%= <%= amountamount %> Kronor are <%= %> Kronor are <%= converter.yenToEuro(dconverter.yenToEuro(d) %> ) %> Euro.Euro.

<%<%}}

%>%></</bodybody>></html></html>


EJB

ExampleExampleA deployment descriptorA deployment descriptor

“Good to understand, when time allows!”

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XML Document HeaderXML Document Header

XML documents start with two general information tags:

1. Specifies the XML version the file use<?xml version=”1.0”?>

2. Specifies the DTD that defines the XML fileProvides the URL to the DTD, you can download it and validate the XML file<!DOCTYPE ejb-jar PUBLIC ”-//Sun Microsystems, Inc.//DTD Enterprise JavaBean 1.1//EN” ”http://java.sun.com/j2ee/dtds/ejb-jar.dtd”>


EJB

XML Descriptor’s BodyXML Descriptor’s Body

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

Bean/ Beans <enterprise-beans>Entity or Session BeansPrimary KeyEnvironment EntriesReference to other BeansReference to External Resources (such as a Database)Security Roles

Bean/Beans Assembly <assembly-description>Transactional attributesSecurity roles & Method permissions

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XML Body exampleXML Body example

<ejb<ejb--jar>jar><description>a body example</description><description>a body example</description><enterprise<enterprise--bean>bean>

<session><session>-- -- --

</session></session><entity><entity>

-- -- --</entity></entity>

-- -- --</enterprise</enterprise--bean>bean>

<assembly<assembly--descriptor> descriptor> -- -- --

</assembly</assembly--descriptor> descriptor> </ejb</ejb--jar>jar>


EJB

<entity><entity><description> a Bean example </description><description> a Bean example </description><ejb<ejb--name>name>PlayerBeanPlayerBean</ejb</ejb--name>name><home><home>com.chess.player.PlayerHomecom.chess.player.PlayerHome</home></home><remote>com.chess.player.Player</remote><remote>com.chess.player.Player</remote><ejb<ejb--class> class> com.chess.player.PlayerBeancom.chess.player.PlayerBean</ejb</ejb--class>class><persistence<persistence--type>Container</persistencetype>Container</persistence--type>type><prim<prim--keykey--class>java.lang.Integer</primclass>java.lang.Integer</prim--keykey--class>class><<primkeyprimkey--field>id</field>id</primkeyprimkey--field>field><reentrant>False</reentrant><reentrant>False</reentrant><<cmpcmp--field><fieldfield><field--name>id</fieldname>id</field--name></name></cmpcmp--field>field>

-- -- --<<cmpcmp--field><fieldfield><field--name>name</fieldname>name</field--name></name></cmpcmp--field>field>

</entity></entity>

XML Bean exampleXML Bean example

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EJB

<ejb-jar><enterprise-beans>...</enterprise-beans>…<assembly-descriptor>

<container-transaction> … </container-transaction> <security-role>

<description>allows to read/write</description><role-name>everyone</role-name>

</security-role><method-permission>

<role-name>everyone</role-name><method>

<ejb-name>myBean</ejb-name><method-name>*</method-name>

</method></method-permission>

</assembly-descriptor>

XML XML Security Roles and Method permissionsSecurity Roles and Method permissions

Documents

Enterprise Java Beans - idt.mdh.se Page 1, 5-Nov-03 Component Technologies EJB Enterprise Java Beans Mikael Åkerholm Page 2, 5-Nov-03 Component Technologies EJB Lecture Stucture Introduction