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Monday February 20, 2006

How to implement cron in Enterprise application One my colleague asked me for implementing cron functionality in J2EE applicationthat is deployed in Sun application server. He needs to execute scheduled commandsin his EJB module. I suggested folowing solution that consists of Timer bean and lifecycle module that starts the timer when the server is started.
I know that better solution is used lifecycle module that is connected to EJB module only. For instance, where the module is deployed the lifecycle listener can invoke the bean. However, Sun Application server doesn't support this type lifecycle listener. The WebLogic server supports lifecycle listeneres on module application level, see here. Other solution is use servlet life cycle listener in web tier but this suggestion adds additional dependency for J2EE application. Since I didn't find better solution I used lifecycle module and Timer bean. Steps are below:

• Create session bean that implements TimedObject interface. Then you should implement ejbTimout method that is invoked when the time expires.
• Then create business method that creates interval timer:

       public void startTimer() {
          TimerService timerServ = context.getTimerService();
           // create interval timer
          Timer timer = timerServ.createTimer(new Date(), 5000, "Timer"); 
      }
    

• Deploy EJB module and then we should create lifecycle listener that invokes startTimer method. Create new J2SE project and add appserv-rt.jar and j2ee.jar on project classpath
• Create new class that implements com.sun.appserv.server.LifecycleListener interface.
• Implements handleEvent method:

       public void handleEvent(LifecycleEvent lifecycleEvent) 
             throws ServerLifecycleException {
          // start timer when server is ready to service requests
          if(lifecycleEvent.getEventType() == LifecycleEvent.READY_EVENT){
              LifecycleEventContext lfcECtx = lifecycleEvent.getLifecycleEventContext();
              try {
                  lfcECtx.log("Try to lookup Timer's bean home: " + EJB_NAME);
                  InitialContext ctx = 
                            lifecycleEvent.getLifecycleEventContext().getInitialContext();
                  Object obj = ctx.lookup(EJB_NAME);
                  TimerSessionRemote timer =
                    ((TimerSessionRemoteHome)PortableRemoteObject.narrow(obj,
                                      TimerSessionRemoteHome.class)).create();
                  lfcECtx.log("Create Timer bean");
                  timer.createTimer();
  

• Build project and copy jar file in lib directory that is in your domain. Don't forget to copy all libraries and EJB's stubs as well.
• Go to web admin console and select node Applications - LifecycleModules. Click New button and create new Lifecycle module.
• Restart application server and ejbTimeout method should be invoked every 5000 ms.