Scheduling and timers - EJB 3 in Action - page 275

7.3.1. Understanding programmatic timers
Ad hoc timers are created via the javax.ejb.TimerService . The TimerService
can either be injected via the @Resource annotation or acquired from the javax.ejb
.SessionContext . Once acquired, TimerService has numerous createTimer
variations that simplify timer creation. Two types of timers can be created with the
TimerService : interval timers and calendar timers. Calendar timers are also known as
cron-based timers and were covered earlier. Interval timers made their appearance in EJB
2.1 and are also supported.
Listing 7.3 contains the TimerService interface. With the exception of the
getTimers() method, all other methods are responsible for creating timers. Each meth-
od returns a javax.ejb.Timer object. The Timer object can be used for retrieving
basic information about the timer, such as whether it's persistent, the time remaining until
it fires, and a method for cancelling the timer. The getHandle() method returns a
javax.ejb.TimerHandle , which supports serialization. The javax.ejb.Timer
object can't be serialized and thus shouldn't be stored in a member variable of a stateful
session bean, JPA entity, and so on. The javax.ejb.TimerHandle provides a method
enabling the current Timer instance to be returned.
Listing 7.3. TimerService interface