OCEJBCD -8.Using Timer Services

OCEJBCD (SCBCD) - 1Z0-895 - Enterprise JavaBeans Developer Certification

8.1. Describe timer services

Timer services is a service of scheduling notifications in the bean container.
(Available for all bean types except from stateful session beans).

Timers services can be created 
-Programmatically, using TimerService interface
-By annotations @Schedule

Functionality that a bean with timer services can perform:

• Create a timer notification callback
• Process a timer notification callback
• Manage timer objects (list notification, cancel timer etc...)

The timers can be classified as:

• Single notifications
• Interval (multiple notifications at specified interval)
• Calendar based schedule 
• second, minute, hour 
• dayOfWeek, dayOfMonth
• month
• year
• Expressions : wildcard (*), list(,), range(-),intervals(/)

8.2. Create a timer notification callback

• By timerService interface
• Single:

          Timer timer = timerService.createSingleActionTimer(data, new             TimerConfig());

• Calendar based: using javax.ejb.ScheduleExpression

          ScheduleExpression schedule = new ScheduleExpression();
          schedule.dayOfMonth("1,Last");//first and last day of the month
          Timer timer = timerService.createCalendarTimer(schedule);

       When a timer expires the container calls the bean's method annotated              with @Timeout (*Note: this method must return void and the argument is optional).

• By annotation

       Example : @Schedule(dayOfWeek="Mon", hour="0")

8.3. Process a timer notification callback 

Example with timerService interface

To execute this bean we need to make a call from a client (for example a servlet class) to the method setTimer that indicates the milliseconds after the timeout will happen: scheduleBean.setTimer(30000);

Results in server console:
2016-03-26T11:58:33.313+0000|Info: TestBean was successfully deployed in 362 milliseconds.
2016-03-26T12:00:26.816+0000|Info: the next timeout is programed Sat Mar 26 12:00:56 GMT 2016 happening in 29968 milliseconds

2016-03-26T12:00:56.787+0000|Info: Timeout occurred

Example with schedule annotation
The following example is a stateless session bean, with a timer scheduled every 1 min.
When it is deployed in the server, after 1 minute the timeout method is called:

Results in server console:
2016-03-26T10:03:00.001+0000|Info: Automatic timeout occured
2016-03-26T10:04:00.002+0000|Info: Automatic timeout occured
2016-03-26T10:05:00.001+0000|Info: Automatic timeout occured
2016-03-26T10:06:00.002+0000|Info: Automatic timeout occured
2016-03-26T10:07:00.002+0000|Info: Automatic timeout occured

8.4. Manage timer objects

-Cancel() - cancel a timer
-getHandle() - obtain a serializable object
-getTimeRemaining()
-getNextTimeout()
-getInfo()

When using container-managed transactions @Timeout can use attributes: Required or RequiredNew to preserve transaction integrity, which means that in case of rollback the timeout will be reset.

OCEJBCD (SCBCD) - 1Z0-895 - Enterprise JavaBeans Developer Certification