enterprise javabeans umer farooq cs6704: design patterns & component frameworksfebruary 25, 2002
TRANSCRIPT
Enterprise JavaBeans
Umer Farooq
CS6704: Design Patterns & Component FrameworksFebruary 25, 2002
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.javaimport 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.javaimport 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.javaimport 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 codeimport 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 Best-in-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/01/12/21/011221hnjavasurvey.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
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