The Java EE 5 Tutorial (PDF) - Oracle Software Downloads

Using theTimer Service
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To retrieve all of a bean’s active timers, call the getTimers method of the TimerService
interface. The getTimers method returns a collection of Timer objects.
Transactions andTimers
An enterprise bean usually creates a timer within a transaction. If this transaction is rolled back,
the timer creation is also rolled back. Similarly, if a bean cancels a timer within a transaction
that gets rolled back, the timer cancellation is rolled back. In this case, the timer’s duration is
reset as if the cancellation had never occurred.
In beans that use container-managed transactions, the @Timeout method usually has the
Required or RequiresNew transaction attribute to preserve transaction integrity. With these
attributes, the EJB container begins the new transaction before calling the @Timeout method. If
the transaction is rolled back, the container will call the @Timeout method at least one more
time.
The timersession Example
The source code for this example is in the
tut-install/javaeetutorial5/examples/ejb/timersession/timersession-ejb/src/java/
directory.
TimerSessionBean is a stateless session bean that shows how to set a timer. In the source code
listing of TimerSessionBean that follows, note the createTimer and @Timeout methods.
Because it’s a business method, createTimer is defined in the bean’s remote business interface
(TimerSession) and can be invoked by the client. In this example, the client invokes
createTimer with an interval duration of 30,000 milliseconds. The createTimer method
creates a new timer by invoking the createTimer method of TimerService.ATimerService
instance is injected by the container when the bean is created. Now that the timer is set, the EJB
container will invoke the timeout method of TimerSessionBean when the timer expires, in
about 30 seconds. Here’s the source code for the TimerSessionBean class:
package com.sun.tutorial.javaee.ejb;
import java.util.logging.Logger;
import javax.annotation.Resource;
import javax.ejb.Stateless;
import javax.ejb.Timeout;
import javax.ejb.Timer;
import javax.ejb.TimerService;
@Stateless
public class TimerSessionBean implements TimerSession {
@Resource
TimerService timerService;
The Java EE 5Tutorial • June 2010