Executing task after deployment of Java EE applica

Question

I have a Java EE application which should start a synchronization process with an external system once after its deployment.

How could I implement this requirement?

Answer 1

Using a ServletContextListener, or a servlet that is initialized at startup, for example. Of course, this becomes much harder if you have multiple deployments of the application in a cluster, and only want this process to be run once.

Answer 2

I tested the suggested solution which uses the @Startup and @PostConstruct annotations. It turned out that Glassfish does not complete the deployment of an application until all methods annotated with @PostConstruct have finished. So in my case the deployment would take from several minutes up to an hour.

But I figured out a different way to achive what I want. The best solution seems to be a timer callback method which cancels its timer after its execution.

@Stateless
public class SynchronisationService {
    @Schedule(hour = "*", minute = "*", persistent = false)
    protected void init(Timer timer)
    {
       doTheSync();

       timer.cancel();
    }
 }

Using a non-persistent timer allows the timer to be re-created if the application server is restarted.

Answer 3

Below are listed a couple of popular methods for getting lifecycle callbacks in JavaEE apps.

Create a javax.servlet.ServletContextListener implementation

If you have a web component to your .ear file (embedded .war) or your deployment is a .war by itself you can add a ServletContextListener to your web.xml and get a callback when the server starts or is shutting down.

Example:

package com.stackoverflow.question

import javax.servlet.ServletContextListener;
import javax.servlet.ServletContextEvent;

public class MyServletContextListener implements ServletContextListener{

   @Override
   public void contextInitialized(ServletContextEvent contextEvent) {
        /* Do Startup stuff. */
   }

   @Override
   public void contextDestroyed(ServletContextEvent contextEvent) {
        /* Do Shutdown stuff. */
   }

}

and then add this configuration to your web.xml deployment descriptor.
$WAR_ROOT/WEB-INF/web.xml.

<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns="http://java.sun.com/xml/ns/javaee">

    <listener>
      <listener-class>com.stackoverflow.question.MyServletContextListener</listener-class>
    </listener>

</web-app>

Create an EJB 3.1 @Startup Bean

This method uses an EJB 3.1 singleton to get a startup and shutdown callback from the server.

import javax.annotation.PostConstruct;
import javax.annotation.PreDestroy;
import javax.ejb.Startup;
import javax.ejb.Singleton;

@Singleton
@Startup
public class LifecycleBean {

  @PostConstruct
  public void init() {
    /* Startup stuff here. */
  }

  @PreDestroy
  public void destroy() {
    /* Shutdown stuff here */
  }

}

Answer 4

You can use the @Startup and @PostConstruct annotations to perform tasks on application startup.