Hello World! -- A basic EJB example

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Hello World!
A basic EJB example

Before starting

This example assumes you have already downloaded and installed OpenEJB in the directory c:\openejb. Refer to the QuickStart Guide if you haven't yet installed OpenEJB.

We also assume that you are running your client from the directory c:\my\app.

Create the bean class

First, create the package where we will place our ejb and application files.

c:\my\app> mkdir org
c:\my\app> mkdir org\acme

In your favorite editor, create the file below.

c:\my\app\org\acme\HelloBean.java

package org.acme;

import java.rmi.RemoteException;
import javax.ejb.*;

public class HelloBean implements SessionBean {
  private SessionContext sessionContext;
  public void ejbCreate() {
  }
  public void ejbRemove() {
  }
  public void ejbActivate() {
  }
  public void ejbPassivate() {
  }
  public void setSessionContext(SessionContext sessionContext) {
    this.sessionContext = sessionContext;
  }
  public String sayHello() throws java.rmi.RemoteException {
    return "Hello World!!!!!";
  }
}

Create the EJB Home interface

c:\my\app\org\acme\HelloHome.java

package org.acme;

import java.rmi.*;
import javax.ejb.*;
import java.util.*;

public interface HelloHome extends EJBHome {
  public HelloObject create() throws RemoteException, CreateException;
}

Create the EJB Object interface

c:\my\app\org\acme\HelloObject.java

package org.acme;

import java.rmi.*;
import javax.ejb.*;
import java.util.*;

public interface HelloObject extends EJBObject {
  public String sayHello() throws RemoteException;
}

Create the ejb-jar.xml

c:\my\app> mkdir META-INF

c:\my\app\META-INF\ejb-jar.xml

<?xml version="1.0" encoding="UTF-8"?>
<ejb-jar>
  <enterprise-beans>
    <session>
      <ejb-name>Hello</ejb-name>
      <home>org.acme.HelloHome</home>
      <remote>org.acme.HelloObject</remote>
      <ejb-class>org.acme.HelloBean</ejb-class>
      <session-type>Stateless</session-type>
      <transaction-type>Container</transaction-type>
    </session>
  </enterprise-beans>
  <assembly-descriptor>
    <container-transaction>
      <method>
        <ejb-name>Hello</ejb-name>
        <method-name>*</method-name>
      </method>
      <trans-attribute>Required</trans-attribute>
    </container-transaction>
  </assembly-descriptor>
</ejb-jar>

Compile the EJB

C:\my\app> javac org\acme\*.java

NOTE

To compile an EJB, you need to have Sun's EJB library in your classpath. One has been included for you in the directory lib/ejb-2.0.jar

Package the EJB

C:\my\app> jar cvf myHelloEjb.jar org META-INF

Deploy the EJB jar

Use the OpenEJB Deploy Tool to deploy your jar.

C:\my\app> cd C:\openejb
C:\openejb> openejb.bat deploy -a -m c:\my\app\myHelloEjb.jar

A basic client application

Create a basic client application to access your HelloWorld bean.

c:\my\app\org\acme\HelloWorld.java

package org.acme;

import javax.rmi.*;
import javax.naming.*;
import java.util.*;

public class HelloWorld {

 public static void main( String args[]) {
  try{
    
    Properties p = new Properties();
    
    //The JNDI properties you set depend
    //on which server you are using.
    p.put("java.naming.factory.initial", ... 
    ...
    
    //Now use those properties to create
    //a JNDI InitialContext with the server.
    InitialContext ctx = new InitialContext( p );
    
    //Lookup the bean using it's deployment id
    Object obj = ctx.lookup("/Hello");
    
    //Be good and use RMI remote object narrowing
    //as required by the EJB specification.
    HelloHome ejbHome = (HelloHome)
        PortableRemoteObject.narrow(obj,HelloHome.class);

    //Use the HelloHome to create a HelloObject
    HelloObject ejbObject = ejbHome.create();
    
    //The part we've all been wainting for...
    String message = ejbObject.sayHello();

    //A drum roll please.
    System.out.println( message );
    
  } catch (Exception e){
    e.printStackTrace();
  }
 }
}

JNDI properties for the Local Server would look like the following. Be sure to read the Local Server documentation if you run into any problems.

Properties p = new Properties();

p.put("java.naming.factory.initial", 
    "org.openejb.core.ivm.naming.InitContextFactory");
p.put("openejb.home", "c:\\openejb");
    
InitialContext ctx = new InitialContext(p);

JNDI properties for the Remote Server would look like the following. Be sure to start the Remote Server before running your application. See the Remote Server documentation for more information on using the Remote Server.

Properties p = new Properties();
p.put("java.naming.factory.initial", 
    "org.openejb.client.JNDIContext");
p.put("java.naming.provider.url", "127.0.0.1:4201");
p.put("java.naming.security.principal", "myuser");
p.put("java.naming.security.credentials", "mypass");
    
InitialContext ctx = new InitialContext(p);

Update the HelloWorld.java to contain the right JNDI properties.

Compile the application

C:\my\app> javac org\acme\HelloWorld.java

NOTE

To compile this application, you need to have Sun's JNDI library in your classpath. One has been included for you in the directory lib/jndi_1.2.1.jar

Run it!

When you run OpenEJB in embedded server mode, you need all the server libraries in your classpath along with your beans and client code. Here is a simple script that will add those classes automactically. Feel free to use this script, or add it's contents to you own scripts.

c:\my\app\RunIt.bat

@echo off

set OPENEJB_HOME=C:\openejb
set PATH=%PATH%;%OPENEJB_HOME%\bin
set JAVA=%JAVA_HOME%\bin\java

set CP=
for %%i in (%OPENEJB_HOME%\lib\*.jar) do call cp.bat %%i 
for %%i in (%OPENEJB_HOME%\dist\*.jar) do call cp.bat %%i 
for %%i in (%OPENEJB_HOME%\beans\*.jar) do call cp.bat %%i 
set CLASSPATH=%JAVA_HOME%\lib\tools.jar;%CP%

%JAVA% %OPTIONS% -Dopenejb.home=%OPENEJB_HOME% org.acme.HelloWorld

Now run the script!

C:\my\app> RunIt

What if it didn't work

If you ran into any problems, first check your openejb.log file at c:\openejb\openejb.log. Look for any lines that begin with "WARN", "ERROR", or "FATAL".

If the log file doesn't help you, email it to the OpenEJB user mailing list and let people know you are using the Hello World example.

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