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Enterprise JavaBeans
Umer Farooq
February 25, 2002
CS6704: Design Patterns & Component Frameworks
Enterprise JavaBeans (EJB)
“Enterprise JavaBeans is the server-side
component architecture for the J2EE
platform. EJB enables rapid and simplified
development of distributed, transactional,
secure and portable Java applications.”
Agenda
 Overview of J2EE platform
 EJB and J2EE?
 Types of EJB
 Life Cycles of EJB
 Client access to EJB
 Code example of an EJB
 Applications using EJB
 Comparison of EJB with Microsoft’s technology!
 Comments/Questions/Discussion
J2EE Platform
 Approach to developing highly scalable internet or intranet
based applications
 Transaction management, life-cycle management, resource
pooling automatically handled
 J2EE application model encapsulates the layers of
functionality in specific types of components
J2EE Application Model
Types of EJB
 Session: Performs a task for a client
 Entity: Represents a business entity object that exists in
persistent storage
 Message-Driven: Acts as a listener for the Java Message
Service API, processing messages asynchronously
 Examples?
Life Cycles
Stateful Session Bean
Life Cycles
Stateless Session Bean
Life Cycles
Entity Bean
Life Cycles
Message-Driven Bean
Client access to EJB
 Client access only through interfaces
 Remote access
May run on a different JVM
 Web component, J2EE client, EJB, etc.
 Location is transparent

A Session Bean Example
 The CartEJB session bean represents a shopping cart in an
online bookstore:
Session bean class (CartBean)
 Home interface (CartHome)
 Remote interface (Cart)
 Two helper classes: BookException and IdVerifier

CartBean.java
import java.util.*;
import javax.ejb.*;
public class CartBean implements SessionBean {
String customerName;
String customerId;
Vector contents;
public void ejbCreate(String person) throws CreateException {
if (person == null) throw new CreateException("Null person not allowed.");
else customerName = person;
customerId = "0";
contents = new Vector();
}
public void ejbCreate(String person, String id) throws CreateException {
if (person == null) throw new CreateException("Null person not allowed.");
else customerName = person;
IdVerifier idChecker = new IdVerifier();
if (idChecker.validate(id)) customerId = id;
else throw new CreateException("Invalid id: "+ id);
contents = new Vector();
}
CartBean.java (cont)
public void addBook(String title) {
contents.addElement(title);
}
public void removeBook(String title) throws BookException {
boolean result = contents.removeElement(title);
if (result == false) throw new BookException(title + "not in cart.");
}
public Vector getContents() {
return contents;
}
public CartBean() {}
public void ejbRemove() {}
public void ejbActivate() {}
public void ejbPassivate() {}
public void setSessionContext(SessionContext sc) {}
}
CartHome.java
import java.io.Serializable;
import java.rmi.RemoteException;
import javax.ejb.CreateException;
import javax.ejb.EJBHome;
public interface CartHome extends EJBHome {
Cart create(String person) throws RemoteException, CreateException;
Cart create(String person, String id) throws RemoteException, CreateException;
}
Cart.java
import java.util.*;
import javax.ejb.EJBObject;
import java.rmi.RemoteException;
public interface Cart extends EJBObject {
public void addBook(String title) throws RemoteException;
public void removeBook(String title) throws BookException, RemoteException;
public Vector getContents() throws RemoteException;
}
Client code
import java.util.*;
import javax.naming.Context;
import javax.naming.InitialContext;
import javax.rmi.PortableRemoteObject;
public class CartClient {
public static void main(String[] args) {
try {
Context initial = new InitialContext();
Object objref = initial.lookup("MyCart");
CartHome home = (CartHome)PortableRemoteObject.narrow
(objref, CartHome.class);
Cart shoppingCart = home.create("Duke DeEarl","123");
shoppingCart.addBook("The Martian Chronicles");
shoppingCart.removeBook("Alice in Wonderland");
shoppingCart.remove();
} catch (BookException ex) {
System.err.println("Caught a BookException: " + ex.getMessage());
} catch (Exception ex) {
System.err.println("Caught an unexpected exception!");
}
}
}
Industry Applications for EJB
 Ford Financial Saves Money, Achieves Business Goals With




Sun – February 20, 2002
Amazon.com's ObjectStore Deployment Ensures Bestin-Class Experience for Customers And Merchants –
February 19, 2002
Borland Wins Again With Web Services Solution for
Linux – February 12, 2002
PointBase Demonstrates World's First Enterprise Data
Synchronization Across Multiple Devices And
Networks – February 12, 2002
Over 40 licencees (who can ship J2EE products)
including Nokia, Oracle, IBM, NEC, Compaq, BEA,
etc.
Comparison with Microsoft
 78 percent viewed J2EE (Java 2 Enterprise Edition) server
software as the most effective platform for building and
deploying Web services to Microsoft’s .Net
(http://www.infoworld.com/articles/hn/xml/01/12/21/01122
1hnjavasurvey.xml)
 What is Microsoft’s corresponding technology?
 Read handout!
Discussion
 When to use which EJB?
 When to use local and remote interfaces?
 What would you choose: Sun or Microsoft? (Remember
Windows had crashed on the last day of your project
submission and you lost it all )
Thank you
([email protected])
References
 http://www.java.sun.com/j2ee\
 http://java.sun.com/j2ee/tutorial/1_3-
fcs/doc/J2eeTutorialTOC.html
 Special Edition Using EJB 2.0 by Dan Chuck Cavaness and
Brian Keeton