A TUTORIAL TO USING EJBs

1

• A TUTORIAL TO USING EJBs
• by
• SHREERAM IYER
• 09/17/2001

2
ENVIRONMENT TOOLS

• Application Server JBOSS
• Web Server/ Servlet Engine Jetty/Tomcat
• Build tool Ant

3
JBOSS

• Implementation of EJB 1.1
• Open Source endeavor
• In-built SQL database Server to handle persistent
  beans
• Very lightweight
• Written completely in Java
• Requires Java System compatible with JDK 1.3

4
JETTY

• Open Source, 100 Java HTTP Servlet Server
• Lightweight
• Extensible
• Implements HTTP 1.1, Servlet API 2.2 and JSP 1.1
  standards
• Jetty integrated into JBOSS

5
ANT

• Standard build tool used with most open source
  Java projects
• Java based build tool
• Configuration files are XML-based
• Calls out target trees where various tasks are
  executed
• Build.xml

6
Home Interface

• InterestHome.java
• package org.jboss.docs.interest
• import java.io.Serializable
• import java.rmi.RemoteException
• import javax.ejb.CreateException
• import javax.ejb.EJBHome
• /
• This interface defines the home' interface for
  the Interest' EJB.
• /
• public interface InterestHome extends EJBHome
• /
• Creates an instance of the InterestBean'
  class on the server, and returns a
• remote reference to an Interest interface on
  the client.
• /
• Interest create() throws RemoteException,
  CreateException

7
Remote Interface

• Interest.java
• package org.jboss.docs.interest
• import javax.ejb.EJBObject
• import java.rmi.RemoteException
• /
• This interface defines the Remote' interface for
  the Interest' EJB. Its
• single method is the only method exposed to the
  outside world. The class
• InterestBean implements the method.
• /
• public interface Interest extends EJBObject
• /
• Calulates the compound interest on the sum
  principle', with interest rate per
• period rate' over periods' time periods.
  This method also prints a message to
• standard output this is picked up by the EJB
  server and logged. In this way we
• can demonstrate that the method is actually
  being executed on the server,
• rather than the client. /
• public double calculateCompoundInterest(double
  principle,

8
The EJB

• InterestBean.java
• package org.jboss.docs.interest
• import java.rmi.RemoteException
• import javax.ejb.SessionBean
• import javax.ejb.SessionContext
• /
• This class contains the implementation for the
  calculateCompoundInterest'
• method exposed by this Bean. It includes empty
  method bodies for the methods
• prescribe by the SessionBean interface these
  don't need to do anything in this
• simple example./
• public class InterestBean implements SessionBean
• /
• Calulates the compound interest on the sum
  principle', with interest rate per
• period rate' over periods' time periods.
  This method also prints a message to
• standard output this is picked up by the EJB
  server and logged. In this way we
• can demonstrate that the method is actually
  being executed on the server,
• rather than the client. /
• public double calculateCompoundInterest(double
  principle,
• double rate, double periods)

9
The EJB

• / Empty method body /
• public void ejbCreate()
• / Empty method body /
• public void ejbRemove()
• / Empty method body /
• public void ejbActivate()
• / Empty method body /
• public void ejbPassivate()
• / Empty method body /
• public void setSessionContext(SessionContext
  sc)

10
EJB Client

• package org.jboss.docs.interest
  // InterestClient.java
• import javax.naming.InitialContext
• import javax.rmi.PortableRemoteObject
• import org.jboss.docs.interest.Interest
• import org.jboss.docs.interest.InterestHome
• / This simple application tests the 'Interest'
  Enterprise JavaBean which is
• implemented in the package 'org.jboss.docs.intere
  st'. For this to work, the
• Bean must be deployed on an EJB server./
• class InterestClient
• / This method does all the work. It creates
  an instance of the Interest EJB on
• the EJB server, and calls its
  calculateCompoundInterest()' method, then prints
• the result of the calculation./
• public static void main(String args)
• // Enclosing the whole process in a single
  try' block is not an ideal way
• // to do exception handling, but I don't
  want to clutter the program up
• // with catch blocks
• try

11
EJB Client

• // Get a reference to the Interest Bean
• Object ref jndiContext.lookup("interes
  t/Interest")
• System.out.println("Got reference")
• // Get a reference from this to the
  Bean's Home interface
• InterestHome home (InterestHome)
• PortableRemoteObject.narrow(ref,
  InterestHome.class)
• // Create an Interest object from the
  Home interface
• Interest interest home.create()
• // call the calculateCompoundInterest()
  method to do the calculation
• System.out.println("Interest on 1000
  units, at 10 per period, compounded over 2
  periods is")
• System.out.println(interest.calculateComp
  oundInterest(1000, 0.10, 2))
• catch(Exception e)
• System.out.println(e.toString())

12
The Deployment Descriptor (DD)

• ejb-jar.xml
• lt?xml version"1.0" encoding"UTF-8"?gt
• ltejb-jargt
• ltdescriptiongtJBoss Interest Sample
  Applicationlt/descriptiongt
• ltdisplay-namegtInterest EJBlt/display-namegt
• ltenterprise-beansgt
• ltsessiongt
• ltejb-namegtInterestlt/ejb-namegt
• lthomegtorg.jboss.docs.interest.InterestHom
  elt/homegt
• ltremotegtorg.jboss.docs.interest.Interestlt
  /remotegt
• ltejb-classgtorg.jboss.docs.interest.Intere
  stBeanlt/ejb-classgt
• ltsession-typegtStatelesslt/session-typegt
• lttransaction-typegtBeanlt/transaction-typegt
  
• lt/sessiongt
• lt/enterprise-beansgt
• lt/ejb-jargt

13
Deployment Descriptor

• lt?xml version"1.0" encoding"UTF-8"?gt
• ltjbossgt
• ltenterprise-beansgt
• ltsessiongt
• ltejb-namegtInterestlt/ejb-namegt
• ltjndi-namegtinterest/Interestlt/jndi-namegt
• lt/sessiongt
• lt/enterprise-beansgt
• lt/jbossgt

14
ROLLING THE BALL

• SET ANT_HOMEY\Ant\Jakarta-ant-1.3
• SET JBOSS_HOMEY\JBoss-2.4.0_Jetty-3.1.RC8-1\JBos
  s-2.4.0_Jetty-3.1.RC8-1
• SET JAVA_HOMEC\jdk1.3.1
• SET PATHPATHANT_HOME\bin
• SET JBOSS_DISTY\JBoss-2.4.0_Jetty-3.1.RC8-1\JBos
  s-2.4.0_Jetty-3.1.RC8-1\jboss

15
STEPS TO BE TAKEN

• Set up all the environment variables
• Start the AppServer using the command run jetty
• Compile the java files
• Make the Deployment Descriptor
• Deploy the EJB
• Run the Application

16
Useful links

• www.jboss.org
• http//jakarta.apache.org
• http//jakarta.apache.org/ant/
• http//jetty.mortbay.com/
• http//jakarta.apache.org/tomcat/
• http//java.sun.com/products/ejb