Configuring an Enterprise Bean With a Java EE Timer

You can configure the following types of enterprise beans to use a Java EE timer:

• EJB 3.0 stateless session beans and message-driven beans.

• EJB 2.1 stateless session beans, entity beans with container-managed persistence, entity beans with bean-managed persistence, and message-driven beans.

To configure an enterprise bean with a Java EE timer, do the following:

1. Acquire the javax.ejb.TimerService in one of the following ways:

   • For an EJB 3.0 enterprise bean, use the @Resource annotation, as Example 25-1 shows.

   • For an EJB 3.0 or EJB 2.1 enterprise bean, use EJBContext or InitalContext method getTimerService, as Example 25-2 shows.

2. Use TimerService method createTimer to create the appropriate type of timer (see the javax.ejb.TimerService API), as Example 25-1 and Example 25-2 show.

   When you create a Timer on an EJB 2.1 entity bean, the container invokes the timeout callback method of that particular entity bean instance identified by its primary key. Timers created for a particular entity bean are removed when the entity bean is removed.

   When you create a Timer on any other type of enterprise beans, the container invokes the timeout callback method on any instance of that type in the pooled state.

3. Implement a timeout callback method.

   This method must not be static or final and must have the following signature:

   void <METHOD>(Timer timer)
   
   

   You can implement a timeout callback method in one of the following ways:

   • For an EJB 3.0 enterprise bean, annotate any bean method using the @Timeout annotation, as Example 25-1 shows.

   • For an EJB 3.0 or EJB 2.1 enterprise bean, implement the javax.ejb.TimedObject interface, as Example 25-2 shows.

Example 25-1 Configuring a Java EE Timer on an EJB 3.0 Stateless Session Bean

import javax.ejb.Stateless;
import javax.annotation.PostConstruct;
import javax.ejb.TimerService;
import javax.ejb.Timer;
import javax.ejb.Timeout;
import javax.ejb.TransactionAttribute;
import javax.ejb.TransactionAttributeType;

@Stateless
public class MySession {
    @PostConstruct
    @TransactionAttribute(value=REQUIRES_NEW)
    public void initialize() {
        @Resource TimerService timerService;
        Timer timer = ts.createTimer(timeout, "Optional-Serializable-Info");
    }

    ...

    @Timeout
    @TransactionAttribute(value=REQUIRES_NEW)
    public void timeoutCallback(Timer timer) {
    ...
    }
}

Example 25-2 Configuring a Java EE Timer on an EJB 2.1 Stateless Session Bean

import javax.ejb.SessionBean;
import javax.ejb.TimerService;
import javax.ejb.TimedObject;

public class MySession implements SessionBean, TimedObject {
    public void initialize() {
        InitialContext ctx = new InitialContext();
        TimerService ts = ctx.getTimerService();
        Timer timer = ts.createTimer(timeout, "Optional-Serializable-Info");
    }
    ...
    public void ejbTimeout(Timer timer) {
    ...
    }
}