Creating Programmatic Timers

To create a timer, the bean invokes one of the create methods of the TimerService interface. The create methods of TimerService allow single-action, interval, or calendar-based timers to be created.

For single-action or interval timers, the expiration of the timer can be expressed either as a duration or an absolute time. The duration is expressed as a the number of milliseconds before a timeout event is triggered. To specify an absolute time, create a java.util.Date object and pass it to either the TimerService.createSingleActionTimer or TimerService.createTimer methods.

Example 16–13 Setting a Programmatic Timer Based On a Duration

The following code sets a programmatic timer that will expire in one minute (6000 milliseconds):

long duration = 6000;
Timer timer = timerService.createSingleActionTimer(duration, new TimerConfig());

Example 16–14 Setting a Programmatic Timer Based On an Absolute Time

The following code sets a programmatic timer that will expire at 12:05 PM on May 1st, 2010, specified as a java.util.Date:

SimpleDateFormatter formatter = new SimpleDateFormatter("MM/dd/yyyy 'at' HH:mm");
Date date = formatter.parse("05/01/2010 at 12:05");
Timer timer = timerService.createSingleActionTimer(date, new TimerConfig());

For calendar-based timers, the expiration of the timer is expressed as a javax.ejb.ScheduleExpression object, passed as a parameter to the TimerService.createCalendarTimer method. The ScheduleExpression class represents calendar-based timer expressions, and has methods that correspond to the attributes described in Creating Calendar-Based Timer Expressions.

Example 16–15 Using ScheduleExpression to Set a Timer

The following code creates a programmatic timer using the ScheduleExpression helper class:

ScheduleExpression schedule = new ScheduleExpression();
schedule.dayOfWeek("Mon");
schedule.hour("12-17, 23");
Timer timer = timerService.createCalendarTimer(schedule);

For details on the method signatures, see the TimerService API documentation at http://java.sun.com/javaee/6/docs/api/javax/ejb/TimerService.html.

The bean described in The timersession Example creates a timer as follows:

Timer timer = timerService.createTimer(intervalDuration,
        "Created new programmatic timer");

In the timersession example, createTimer is invoked in a business method, which is called by a client.

Timers are persistent by default. If the server is shut down (or even crashes), persistent timers are saved and will become active again when the server is restarted. If a persistent timer expires while the server is down, the container will call the @Timeout method when the server is restarted.

Non-persistent programmatic timers are created by calling TimerConfig.setPersistent(false) and passing the TimerConfig object to one of the timer creation methods.

The Date and long parameters of the createTimer methods represent time with the resolution of milliseconds. However, because the timer service is not intended for real-time applications, a callback to the @Timeout method might not occur with millisecond precision. The timer service is for business applications, which typically measure time in hours, days, or longer durations.