
 Hello World! A basic EJB example
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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.
Windows
c:\my\app> mkdir org
c:\my\app> mkdir org\acme
Linux/Unix
[user@host app]# mkdir org
[user@host 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!!!!!";
}
}
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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;
}
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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;
}
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Create the ejb-jar.xml
Create a META-INF directory to put your ejb-jar.xml into.
Windows
c:\my\app> mkdir META-INF
Linux/Unix
[user@host app]# mkdir META-INF
Create am ejb-jar.xml file in your META-INF directory.
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>
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Compile the EJB
Compile your bean.
Windows
c:\my\app> javac org\acme\*.java
Linux/Unix
[user@host app]# javac org/acme/*.java
Make sure you don't make the mistake of trying to compile your classes
while sitting inside the org/acme/ directory.
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-1.0.jar
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Package the EJB
Now, package your EJB classes and your META-INF directory into a jar.
Windows
C:\my\app> jar cvf myHelloEjb.jar org META-INF
Linux/Unix
[user@host app]# jar cvf myHelloEjb.jar org META-INF
That command should give you output like the following.
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added manifest
adding: org/(in = 0) (out= 0)(stored 0%)
adding: org/acme/(in = 0) (out= 0)(stored 0%)
adding: org/acme/HelloBean.class(in = 946) (out= 467)(deflated 50%)
adding: org/acme/HelloObject.class(in = 234) (out= 177)(deflated 24%)
adding: org/acme/HelloHome.class(in = 263) (out= 188)(deflated 28%)
ignoring entry META-INF/
ignoring entry META-INF/MANIFEST.MF
adding: META-INF/ejb-jar.xml(in = 733) (out= 319)(deflated 56%)
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Check to make sure at least the three classes are there and the
ejb-jar.xml is there and that everything is in the directories you see
above.
Deploy the EJB jar
Use the OpenEJB Deploy Tool to deploy your jar.
Windows
C:\my\app> cd C:\openejb
C:\openejb> openejb.bat deploy -a -m c:\my\app\myHelloEjb.jar
Linux/Unix
[user@host app]# cd /openejb
[user@host openejb]# ./openejb.sh deploy -a -m /my/app/myHelloEjb.jar
NOTE |
Since the OpenEJB deployment tool writes to your jar file, make sure that
no other programs are using it when you deploy (i.e. if you use an editor
such as Forte for Java to create the jar file, that editor may still be
using it). If you get an error such as "Error in writing existing jar
file" close any programs that may be using the jar and try deploying
again.
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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();
p.put("java.naming.factory.initial", "org.openejb.client.RemoteInitialContextFactory");
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 );
Object obj = ctx.lookup("/Hello");
HelloHome ejbHome = (HelloHome)
PortableRemoteObject.narrow(obj,HelloHome.class);
HelloObject ejbObject = ejbHome.create();
String message = ejbObject.sayHello();
System.out.println( message );
} catch (Exception e){
e.printStackTrace();
}
}
}
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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.client.LocalInitialContextFactory");
p.put("openejb.home", "c:\\openejb");
InitialContext ctx = new InitialContext(p);
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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.RemoteInitialContextFactory");
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);
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Update the HelloWorld.java to contain the right JNDI properties.
Compile the application
Compile your client code. Don't forget to add your EJBs in the
classpath!
Windows
C:\my\app> javac org\acme\HelloWorld.java
Linux/Unix
[user@host 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
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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.
Example Windows Batch script.
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
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Example Linux/Unix Batch script.
/my/app/RunIt.sh |
#!/bin/sh
# Set OPENEJB_HOME to the full path where you
# installed your OpenEJB distribution
export OPENEJB_HOME=/openejb
# Set JAVA_HOME to the full path where you
# installed your JDK distribution
export JAVA_HOME=/usr/java/jdk1.3.1
export PATH=${PATH}:${OPENEJB_HOME}/bin
export JAVA=${JAVA_HOME}/bin/java
export CP=
CP=`echo $OPENEJB_HOME/lib/*.jar | tr ' ' ':'`:${CP}
CP=`echo $OPENEJB_HOME/dist/*.jar | tr ' ' ':'`:${CP}
CP=`echo $OPENEJB_HOME/beans/*.jar | tr ' ' ':'`:${CP}
export CLASSPATH=$JAVA_HOME/lib/tools.jar:${CP}
$JAVA -Dopenejb.home=$OPENEJB_HOME org.acme.HelloWorld
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Now run the script!
Windows
C:\my\app> RunIt
Linux/Unix
[user@host app]# ./RunIt.sh
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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