Use the API defined in Java EE to operate the Timer Service from the Enterprise Bean. Generate an EJB timer to execute a processing for which a time is specified. Specify the time for timeout in the EJB timer. The generated EJB timer is managed in the EJB container and once the time for timeout is reached, the Enterprise Bean method is called back by the EJB container. The method that is called back at this point is called the timeout method.

The following figure shows an overview of the Timer Service processing:

Figure 2-17 Overview of the Timer Service operation

The following two types can be set as the types of EJB timers:

• single-event timer
  The single-event timer is the EJB timer for executing the timeout method only once.
  The timeout is set either by specifying the time of executing the timeout method or by specifying the time period from invocation of the method for generating the EJB timer until execution of the timeout method.
  You can generate this timer using the following methods of the javax.ejb.TimerService interface:
  
  • createTimer(long duration, Serializable info) method
  • createTimer(Date expiration, Serializable info) method
  • createSingleActionTimer method
• interval timer
  The interval timer is the EJB timer for repeated execution of the timeout method at fixed intervals.
  The timeout is set either by specifying the time of executing the first timeout method or by specifying the time period from invocation of the method for generating the EJB timer until execution of the first timeout method. Apart from this setting, specify the timeout interval for executing the timeout method from second time onwards. This is the interval from one timeout to the next.
  You can generate the timer using the following methods of the javax.ejb.TimerService interface:
  
  • createTimer(long initialDuration, long intervalDuration, Serializable info) method
  • createTimer(Date initialExpiration, long intervalDuration, Serializable info) method
  • createIntervalTimer method
• calendar-based timer
  The calendar-based timer is the EJB timer to execute the timeout method on the date and time specified in the calendar format. You can specify single or multiple values. Also you can specify a wild card or range. For details on the method of specifying the calendar-based timer, see 2.12.7(3) Method for specifying a schedule in calendar format.
  You can generate the javax.ejb.TimerService interface with the following method:
  
  • createCalendarTimer method
  You can also create the method with the @Schedule annotation. For details, see 2.12.3 Automatically generating an EJB timer.
  

The following table describes the types of timers that can be set as an EJB timer as well as example settings:

Table 2-32 Types of timers that can be set as EJB timer and example settings

Timer type	Example settings	Description
single-event	2006/4/15 12:00	Execute the timeout method only once at 2006/4/15 12:00.
	After 24 hours	Execute the timeout method only once, after 24 hours from the generation of EJB timer.
Interval	2006/4/1 24 hours interval from 12:00	Execute the first timeout method at 01.04.06 12:00. After this, repeat the timeout method at an interval of 24 hours.
	10 hours interval after 24 hours	Execute the first timeout method after 24 hours from the generation of EJB timer. After this, repeat the timeout method at an interval of 10 hours.
calendar-based	First day of every month 12:00	Execute the timeout method on the first day of every month at 12:00

The following figure shows the operations of the single-event timer and interval timer from among the EJB timers. This figure shows the operations of the single-event timer that calls back the timeout method only once at 2:00 and the interval timer that calls back the timeout method at an interval of two hours, starting from 2:00.

Figure 2-18 Operations of the single-event timer and interval timer

The following table describes the support status of the Timer Service functionality defined in the Java EE specifications:

Table 2-33 Support status of the Timer Service functionality defined in the Java EE specifications

Timer Service functionality defined in the Java EE specifications	Support status
Transaction	Y
EJB timer persistence	--#
Acquiring the TimerService objects (DI, JNDI lookup, EJBContext)	Y
Specifying the timeout method (annotation, TimedObject implementation)	Y
Specifying the timeout methods (specifying by DD)	--

Legend:

Y: Can be used

--: Cannot be used

#

Specification of the persistent attribute of the @Schedule annotation is also not effective.

If a J2EE server is restarted due to a failure, the EJB timer that was in use before restart is not inherited. For details on automatic generation of the EJB timer during invocation of a J2EE server, see 2.12.3 Automatically generating an EJB timer.

The following table describes the support status of Timer Service functionality for various types of Enterprise Beans:

Table 2-34 Support status of Timer Service functionality for various types of Enterprise Beans

Timer Service functionality	Message-driven Bean	Session Bean			Entity Bean
		Stateful Session Bean	Stateless Session Bean	Singleton Session Bean
Acquiring the TimerService objects	N	--	Y	Y	N
Operating the objects related to the Timer Service (TimerService, Timer, TimerHandle)	N	Y	Y	Y	N
Automatic generation of the timer with annotation	N	--	Y	Y	N

Legend:

Y: Can be used

N: Cannot be used

--: Cannot be used (J2EE specifications)

The Timer Service supports transactions. Specifically, the generation of an EJB timer, deletion of the EJB timer, and the timeout method comply with the transactions. The transaction management of the timeout method is explained below:

For details on generating the EJB timer, see 2.12.2 Operation during the generation of an EJB timer and execution of a callback, and for details on deleting the EJB timer, see 2.12.4 Deleting the EJB timer.

(a) Transaction attributes that can be set in the timeout method

In the timeout method, you can select either BMT or CMT for transaction management.

If CMT is selected, the transaction attributes that can be specified in the timeout method are as follows:

• Required attribute
• RequiresNew attribute
• NotSupported attribute

If an attribute other than those described above is specified, the J2EE applications fail to start.

(b) Transaction management for callback of the timeout method

In the timeout method, when the Required attribute or the RequiresNew attribute is specified in CMT, callback will be retried if the transaction rolls back during callback of the timeout method. For details on retrying callback, see 2.12.5(2) Retrying callback of the timeout method.