95-702 Organizational Communication Technologies 1 Enterprise Java Beans Detail.

95-702 Organizational Communication Technologies

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Enterprise Java Beans

Detail


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Notes from:

“Advanced Java 2 Platform How to Program” Deitel Deitel Santry

“Thinking in Enterprise Java” Bruce Eckel et. Al.

Sun documentation and J2EE Tutorial http://java.sun.com


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Benefits of Enterprise Beans

• Simplify development of large, distributed applications

• The developer can concentrate on business problems

• The EJB container handles transaction management and security authorization

• Portable – may be moved to other J2EE containers


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Benefits of Enterprise Beans(2)

• Scalable – the components may be distributed across many machines

• Location Transparency – the client should not be concerned with the location of the bean

• Transaction management - ensures data integrity (over concurrent access of shared resources)

• Promotes thin clients and web services


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Entity Bean

• Each entity bean has a unique identifier called its primary key

• The primary key can be used by the client to locate the bean

• Each bean represents a row in its table• Rows may have columns that reference other

entity beans (students take courses)• These relationships may be managed by the

bean or by the container (container managed relationships)


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Relationships OrderEJB CusomerEJB 1 Many 1

Many

LineItemEJB ProductEJB

Many 1

A relationship field is like a foreign key in a database.If a b then a “knows about” or “holds a pointer to” b.


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Entity Bean Life Cycle (From Sun)

Does not exist

Pool of available instances

-- Ready to havebusiness methods called

-- Has an identity

setEntityContext unsetEntityContext

ejbActivate ejbPassivateClient callscreate and container calls ejbCreateand ejbPostCreate

Client callsremove andcontainer callsejbRemove

Client initiates

Containerinitiates


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A Typical Entity Bean Needs

• A Home interface defining the create and finder methods

• A Component interface defining the business methods a client may call

• An implementation of the Component interface

• Deployment descriptors


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A Home Interface

import javax.ejb.*; // From Eckelimport java.util.Collection;import java.rmi.RemoteException; public interface MovieHome extends EJBHome { public Movie create(Integer id, String title) throws RemoteException, CreateException; public Movie findByPrimaryKey(Integer id) throws RemoteException, FinderException;}


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A Component Interfaceimport javax.ejb.*; // From Eckelimport java.rmi.RemoteException; /** * A movie, with id and title. * * Note that there is no setId() method in the * interface, to prevent clients from arbitrarily * changing a movie's primary key. */public interface Movie extends EJBObject { public Integer getId() throws RemoteException; public String getTitle() throws RemoteException; public void setTitle(String title) throws RemoteException;}


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The Container Implements the component interface (From Eckel)


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import javax.ejb.CreateException; // From Eckelimport javax.ejb.EntityBean;import javax.ejb.EntityContext; public abstract class MovieBean implements EntityBean { // Container notifications methods public Integer ejbCreate(Integer id, String title) throws CreateException { if (id == null) throw new CreateException("Primary key cannot be null"); if (id.intValue() == 0) throw new CreateException("Primary key cannot be zero"); setId(id); setTitle(title); return null; }


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public void ejbPostCreate(Integer id, String title) {} // Called by public void ejbLoad() {} // container public void ejbStore() {} public void ejbRemove() {} public void ejbActivate() {} public void ejbPassivate() {} public void setEntityContext(EntityContext ctx) {} public void unsetEntityContext() {} // Business methods provided by container public abstract void setId(Integer id); public abstract String getTitle(); public abstract void setTitle(String title); public abstract Integer getId();}

// From Eckel


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Deployment Descriptor<ejb-jar> // From Eckel <enterprise-beans> <entity> <ejb-name>Movie</ejb-name> <home>javatheater.ejb.MovieHome</home> <remote>javatheater.ejb.Movie</remote> <ejb-class> javatheater.ejb.implementation.MovieBean </ejb-class> <persistence-type>Container</persistence-type> <prim-key-class>java.lang.Integer</prim-key-class> <reentrant>False</reentrant> <cmp-version>2.x</cmp-version> <abstract-schema-name>Movie</abstract-schema-name> <cmp-field><field-name>id</field-name>-</cmp-field> <cmp-field><field-name>title</field-name>-</cmp-field> <primkey-field>id</primkey-field> </entity> </enterprise-beans></ejb-jar>


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Client (From Eckel)import javax.naming.*;import javatheater.ejb.*; public class MovieClient { public static void main(String[] args) throws Exception { javax.naming.Context initial = new javax.naming.InitialContext(); Object objRef = initial.lookup("javatheater/Movie"); MovieHome movieHome = (MovieHome) javax.rmi.PortableRemoteObject.narrow( objRef, MovieHome.class);


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// Generate a primary key value int pkValue = (int) System.currentTimeMillis() % Integer.MAX_VALUE; // Create a new Movie entity Movie movie = movieHome.create( new Integer(pkValue), "A Bug’s Life" ); // As a test, locate the newly created entity movie = movieHome.findByPrimaryKey(new Integer(pkValue)); // Access the bean properties System.out.println(movie.getId()); System.out.println(movie.getTitle()); // Remove the entity movie.remove(); }}


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Session Bean

• Represents a single client inside the J2EE server

• Is not persistent• May be stateful (holding the

conversational state of one client)• May be stateless (the container may

assign any bean to any client)• Is the only bean that may implement a

web service


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Life Cycle of Stateful Session Bean

Does not exist

Ready for businessmethods to be called

Passive

From Sun

Client calls create.Container calls setSessionContextand then callsejbCreate

Container calls ejbPassivate beforepassivating

After activation the container callsejbActivate

Client calls remove, container calls ejbRemove


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Life Cycle of a Stateless Session Bean (from Sun)

Does not exist

Ready

setSessionContextejbCreate

ejbRemove


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A Typical Session Bean Has

• A Remote Interface defining the business methods a client will call

• A Home Interface for lifecycle management

• An enterprise bean class


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Session Bean Remote Interface(From Sun)

import javax.ejb.EJBObject;import java.rmi.RemoteException;import java.math.*;public interface Converter extends EJBObject { public BigDecimal dollarToYen(BigDecimal dollars) throws RemoteException; public BigDecimal yenToEuro(BigDecimal yen) throws RemoteException; }


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The Home Interface

import java.io.Serializable;import java.rmi.RemoteException;import javax.ejb.CreateException;import javax.ejb.EJBHome;public interface ConverterHome extends

EJBHome { Converter create() throws RemoteException, CreateException;}


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The Session Bean Class

import java.rmi.RemoteException;import javax.ejb.SessionBean;import javax.ejb.SessionContext;import java.math.*;public class ConverterBean implements SessionBean { BigDecimal yenRate = new BigDecimal("121.6000"); BigDecimal euroRate = new BigDecimal("0.0077");

public BigDecimal dollarToYen(BigDecimal dollars) { BigDecimal result = dollars.multiply(yenRate); return result.setScale(2,BigDecimal.ROUND_UP); }


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public BigDecimal yenToEuro(BigDecimal yen) { BigDecimal result = yen.multiply(euroRate); return result.setScale(2,BigDecimal.ROUND_UP);}public ConverterBean() {}public void ejbCreate() {}public void ejbRemove() {}public void ejbActivate() {}public void ejbPassivate() {}public void setSessionContext(SessionContext sc) {}}


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The Session Bean Clientimport javax.naming.Context;import javax.naming.InitialContext;import javax.rmi.PortableRemoteObject;import java.math.BigDecimal;public class ConverterClient {public static void main(String[] args) {try { Context initial = new InitialContext(); Object objref = initial.lookup ("java:comp/env/ejb/SimpleConverter"); ConverterHome home = (ConverterHome)PortableRemoteObject.narrow(objref, ConverterHome.class);


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Converter currencyConverter = home.create(); BigDecimal param = new BigDecimal ("100.00"); BigDecimal amount = currencyConverter.dollarToYen(param); System.out.println(amount); amount = currencyConverter.yenToEuro(param); System.out.println(amount); System.exit(0); } catch (Exception ex) { System.err.println("Caught an unexpected exception!"); ex.printStackTrace(); } }}


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Message Driven Bean

• Handles asynchronous messages• Normally acts as a JMS message listener• The message may have originated from an

application client, another enterprise bean, a web component or a non-Java application that can generate messages

• Like a stateless session bean but with no interfaces

• All operations within onMessage may be in a transaction context (the message is redelivered on rollback)


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From Sun


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On The Client

// locate the connection factory and queue

connectionFactory =

(ConnectionFactory) jndiContext.lookup

("java:comp/env/jms/MyConnectionFactory");

destination =

(Queue) jndiContext.lookup("java:comp/env/jms/QueueName");


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// Next, the client creates the queue connection, session, and sender:

connection = connectionFactory.createConnection();session = connection.createSession(false, Session.AUTO_ACKNOWLEDGE);

messageProducer = session.createProducer(destination);

// Finally, the client sends several messages to the queue:

message = session.createTextMessage(); for (int i = 0; i < NUM_MSGS; i++) { message.setText("This is message " + (i + 1)); System.out.println("Sending message: " + message.getText()); messageProducer.send(message); }


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JMS Message TypesJMS Message TypesMessage Type Body Contains

TextMessageA java.lang.String object (for example, an XML document).

MapMessageA set of name/value pairs, with names as String objects and values asprimitive types in the Java programming language. The entries can beaccessed sequentially by enumerator or randomly by name. The orderof the entries is undefined.


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BytesMessageA stream of uninterpreted bytes. This message type is for literallyencoding a body to match an existing message format.

StreamMessageA stream of primitive values in the Java programming language, filledand read sequentially.

ObjectMessage A Serializable object in the Java programming language.


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On the serverpublic void onMessage(Message inMessage) { TextMessage msg = null; try { if (inMessage instanceof TextMessage) { msg = (TextMessage) inMessage; System.out.println("MESSAGE BEAN: Message received: " +msg.getText()); } else { System.out.println("Message of wrong type: " + inMessage.getClass().getName()); } } catch (JMSException e) { e.printStackTrace(); mdc.setRollbackOnly(); } catch (Throwable te) { te.printStackTrace(); } }


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The Web Service as an EJB


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From The J2EE Tutorial


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From The J2EE Tutorial


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The Web Service as an EJB

• A Web service client can access J2EE applications in two ways.

• First, the client can access a Web service created with JAX-RPC. Behind the scenes, JAX-RPC uses a servlet to implement the Web service.

• Second, a Web service client can access a stateless session bean through the service endpoint interface of the bean. Other types of enterprise beans cannot be accessed by Web service clients.


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A Stateless Session Bean as a Web Service

• The client need not know that its interacting with a Java EJB

• It calls the bean like it calls any other web service


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The Web Service Endpoint Interface

package helloservice;

import java.rmi.RemoteException;

import java.rmi.Remote;

public interface HelloIF extends Remote {

public String sayHello(String name)

throws RemoteException;

}

The client cannotsee that it’s interactingwith an EJB


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The Web Service Session Beanpackage helloservice;import java.rmi.RemoteException; import javax.ejb.SessionBean;import javax.ejb.SessionContext;

public class HelloServiceBean implements SessionBean {

public String sayHello(String name) {

return "Hello " + name + "from HelloServiceEJB"; } public HelloServiceBean() {} public void ejbCreate() {} public void ejbRemove() {} public void ejbActivate() {} public void ejbPassivate() {} public void setSessionContext(SessionContext sc) {}}

If we added remote and homeInterfaces then this bean couldalso be called using in the traditionalmanner – with remote references. No change to the bean would be necessary.

WSDL can be generated and allof the previous clients will work.

95-702 Organizational Communication Technologies 1 Enterprise Java Beans Detail.

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