Configuring Regularly Scheduled Timers (Cron Timers)

You can schedule a timer to execute regularly at specified intervals. In the UNIX world, these are known as cron timers.

The following are examples of the different methods you can use in scheduling a cron timer. Where there is an asterisk, all values are valid.

Example 11-1 How to Configure Different Timers

20  * * * * --> 20 minutes after every hour, such as 00:20, 01:20, and so on
 5 22 * * * --> Every day at 10:05 P.M.
 0  8 1 * * --> First day of every month at 8:00 A.M. 
 0  8 4 7 * --> The fourth of July at 8:00 A.M. 
15 12 * * 5 --> Every Friday at 12:15 P.M.

The format of a cron time variable includes five time fields:

• Minute: 0-59

• Hour: 0-23

• Day of the Month: 1-31

• Month: 1-12 or specify with the following strings: Jan, Feb, Mar, Apr, May, Jun, Jul, Aug, Sep, Oct, Nov, Dec

• Day of the Week: 0-7 or with the following strings: Sun, Mon, Tue, Wed, Thu, Fri, Sat. Both 0 and 7 signify Sunday.

You can define complex timers by specifying multiple values in a field, separated by commas or a dash.

Example 11-2 Complex Timers

0  8   *   * 1,3,5 --> Every Monday, Wednesday, and Friday at 8:00 A.M.
0  8  1,15 *  *   --> The first and 15th of every month at 8:00 A.M.
0 8-17 *   * 1-5  --> Every hour from 8 A.M. through 5 P.M., Monday through Friday

You can create cron timers either through the createTimer method that takes a String with the previous five fields in it—separated by spaces—or with the createTimer method that has variables for each field. To create the cron timers, use the following Oracle-specific createTimer APIs:

EJBTimer createTimer(String cronline, Serializable info)  throws IllegalArgumentException, IllegalStateException;

EJBTimer createTimer(int minute, int hour, int dayOfMonth, int month, int dayOfWeek, int year, Serializable info) throws IllegalArgumentException, IllegalStateException;

Create the cron timers in the same manner as other timers by retrieving the extended Oracle-specific timer service, and schedule a cron timer using the createTimer method. However, since cron timers are Oracle-specific, you cast the returned object as an EJBTimerService object. The following example provides a String with the five variables separated by spaces. The timer is scheduled to execute every minute.

import oracle.ias.container.timer.EJBTimer;
import oracle.ias.container.timer.EJBTimerService;
...
String cron = "1 * * * *";  
EJBTimerService ets = (EJBTimerService) ctx.getTimerService();
EJBTimer et = ets.createTimer(cron, info);

You can also provide a class that is to be invoked within the createTimer method, as follows:

EJBTimer createTimer(String cronline, String className, Serializable info) throws IllegalArgumentException,  IllegalStateException;

EJBTimer createTimer(int minute, int hour, int dayOfMonth, int month, int dayOfWeek, String className, Serializable info) throws IllegalArgumentException, IllegalStateException;

For arbitrary Java classes, the info variable can be either null or be a String[] of parameters to pass to the main method of the class.

For example, you can have the mypackage.MyClass invoked when the et timer fires:

EJBTimerService ets = (EJBTimerService) ctx.getTimerService();
EJBTimer et = ets.createTimer(cron,"mypackage.MyClass", info);

You must provide a main method within the mypackage.MyClass, which is used as the entry point, as follows:

public static void main( String args[] )