Enterprise JavaBeans Umer Farooq

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Enterprise JavaBeansUmer Farooq
CS6704 Design Patterns Component Frameworks
February 25, 2002
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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.

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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 Microsofts technology!
• Comments/Questions/Discussion

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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

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J2EE Application Model
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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?

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Life Cycles
Stateful Session Bean
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Life Cycles
Stateless Session Bean
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Life Cycles
Entity Bean
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Life Cycles
Message-Driven Bean
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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

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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

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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()
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CartBean.java (cont)

• public void addBook(String title)
• contents.addElement(title)
• public void removeBook(String title) throws
  BookException
• boolean result contents.removeElement(titl
  e)
• 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)
  

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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

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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
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Client code
import java.util. import javax.naming.Context i
mport 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!")
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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.

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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 Microsofts .Net
• (http//www.infoworld.com/articles/hn/xml/01/12/2
  1/011221hnjavasurvey.xml)
• What is Microsofts corresponding technology?
• Read handout!

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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
• (ufarooq_at_vt.edu)

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References

• http//www.java.sun.com/j2ee\
• http//java.sun.com/j2ee/tutorial/1_3-fcs/doc/J2ee
  TutorialTOC.html
• Special Edition Using EJB 2.0 by Dan Chuck
  Cavaness and Brian Keeton