EJB - Timer Service

Timer Service is a mechanism by which scheduled application can be build. For example, salary slip generation on the 1st of every month. EJB 3.0 specification has specified @Timeout annotation, which helps in programming the EJB service in a stateless or message driven bean. EJB Container calls the method, which is annotated by @Timeout.

EJB Timer Service is a service provided by EJB container, which helps to create timer and to schedule callback when timer expires.

Steps to Create Timer

Inject SessionContext in bean using @Resource annotation −

@Stateless
public class TimerSessionBean {

   @Resource
   private SessionContext context;
   ...
}

Use SessionContext object to get TimerService and to create timer. Pass time in milliseconds and message.

public void createTimer(long duration) {
   context.getTimerService().createTimer(duration, "Hello World!");
}

Steps to Use Timer

Use @Timeout annotation to a method. Return type should be void and pass a parameter of type Timer. We are canceling the timer after first execution otherwise it will keep running after fix intervals.

@Timeout
public void timeOutHandler(Timer timer) {
   System.out.println("timeoutHandler : " + timer.getInfo());        
   timer.cancel();
}

Example Application

Let us create a test EJB application to test Timer Service in EJB.

EJBComponent (EJB Module)

TimerSessionBean.java

package com.howcodex.timer;

import javax.annotation.Resource;
import javax.ejb.SessionContext;
import javax.ejb.Timer;
import javax.ejb.Stateless;
import javax.ejb.Timeout;

@Stateless
public class TimerSessionBean implements TimerSessionBeanRemote {

   @Resource
   private SessionContext context;

   public void createTimer(long duration) {
      context.getTimerService().createTimer(duration, "Hello World!");
   }

   @Timeout
   public void timeOutHandler(Timer timer) {
      System.out.println("timeoutHandler : " + timer.getInfo());        
      timer.cancel();
   }
}

TimerSessionBeanRemote.java

package com.howcodex.timer;

import javax.ejb.Remote;

@Remote
public interface TimerSessionBeanRemote {
   public void createTimer(long milliseconds);
}

• As soon as you deploy the EjbComponent project on JBOSS, notice the jboss log.

• JBoss has automatically created a JNDI entry for our session bean − TimerSessionBean/remote.

• We will using this lookup string to get remote business object of type − com.howcodex.timer.TimerSessionBeanRemote

JBoss Application Server Log Output

...
16:30:01,401 INFO  [JndiSessionRegistrarBase] Binding the following Entries in Global JNDI:
   TimerSessionBean/remote - EJB3.x Default Remote Business Interface
   TimerSessionBean/remote-com.howcodex.timer.TimerSessionBeanRemote - EJB3.x Remote Business Interface
16:30:02,723 INFO  [SessionSpecContainer] Starting jboss.j2ee:jar=EjbComponent.jar,name=TimerSessionBean,service=EJB3
16:30:02,723 INFO  [EJBContainer] STARTED EJB: com.howcodex.timer.TimerSessionBeanRemote ejbName: TimerSessionBean
...   

EJBTester (EJB Client)

jndi.properties

java.naming.factory.initial=org.jnp.interfaces.NamingContextFactory
java.naming.factory.url.pkgs=org.jboss.naming:org.jnp.interfaces
java.naming.provider.url=localhost

• These properties are used to initialize the InitialContext object of java naming service.

• InitialContext object will be used to lookup stateless session bean.

EJBTester.java

package com.howcodex.test;
   
import com.howcodex.stateful.TimerSessionBeanRemote;
import java.io.BufferedReader;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.List;
import java.util.Properties;
import javax.naming.InitialContext;
import javax.naming.NamingException;

public class EJBTester {

   BufferedReader brConsoleReader = null; 
   Properties props;
   InitialContext ctx;
   {
      props = new Properties();
      try {
         props.load(new FileInputStream("jndi.properties"));
      } catch (IOException ex) {
         ex.printStackTrace();
      }
      try {
         ctx = new InitialContext(props);            
      } catch (NamingException ex) {
         ex.printStackTrace();
      }
      brConsoleReader = 
      new BufferedReader(new InputStreamReader(System.in));
   }
   
   public static void main(String[] args) {

      EJBTester ejbTester = new EJBTester();

      ejbTester.testTimerService();
   }
   
   private void showGUI() {
      System.out.println("**********************");
      System.out.println("Welcome to Book Store");
      System.out.println("**********************");
      System.out.print("Options \n1. Add Book\n2. Exit \nEnter Choice: ");
   }
   
   private void testTimerService() {
      try {
         TimerSessionBeanRemote timerServiceBean = (TimerSessionBeanRemote)ctx.lookup("TimerSessionBean/remote");

         System.out.println("["+(new Date()).toString()+ "]" + "timer created.");
         timerServiceBean.createTimer(2000);            

      } catch (NamingException ex) {
         ex.printStackTrace();
      }
   }
}

EJBTester is doing the following tasks.

• Load properties from jndi.properties and initialize the InitialContext object.

• In testTimerService() method, jndi lookup is done with the name - "TimerSessionBean/remote" to obtain the remote business object (timer stateless EJB).

• Then createTimer is invoked passing 2000 milliseconds as schedule time.

• EJB Container calls the timeoutHandler method after 2 seconds.

Run Client to Access EJB

Locate EJBTester.java in project explorer. Right click on EJBTester class and select run file.

Verify the following output in Netbeans console.

run:
[Wed Jun 19 11:35:47 IST 2013]timer created.
BUILD SUCCESSFUL (total time: 0 seconds)

JBoss Application Server Log Output

You can find the following callback entries in JBoss log

...
11:35:49,555 INFO  [STDOUT] timeoutHandler : Hello World!
...