Creating Calendar Based Timers in Java EE 6

Java EE 6 allows developers to create application timers that are initialized when either a Stateless Session Bean, a Singleton Bean or a Message Driven Bean are deployed to the application server.

To indicate that a method on any of these beans is to be invoked on a timed basis, the method must be annotated with either the @Schedule annotation (for single timer schedules), or the @Schedules annotation (for multiple timer schedules).

The code below shows a very simple Stateless Session Bean configured with 2 scheduled timers.  The first timer is configured with one schedule whereas the second is configured with 2 schedules.

package com.acme.timer;

import javax.ejb.Schedule;
import javax.ejb.Schedules;
import javax.ejb.Stateless;
import javax.ejb.Timer;

@Stateless
public class CalendarTimer {

  @SuppressWarnings("unused")
  @Schedule(second = "*/10", minute = "*", hour = "8-17", dayOfWeek = "Mon-Fri", dayOfMonth = "*", month = "*", year = "*", info = "Scheduled Timer")
  private void scheduledTimeout(final Timer t) {
    System.out.println(t.getInfo().toString() + " called at: "
        + new java.util.Date());
  }

  @SuppressWarnings("unused")
  @Schedules({
      @Schedule(second = "15", minute = "*", hour = "8-17", dayOfWeek = "Mon-Fri", dayOfMonth = "*", month = "*", year = "*", info = "2nd Scheduled Timer"),
      @Schedule(second = "45", minute = "*", hour = "8-17", dayOfWeek = "Mon-Fri", dayOfMonth = "*", month = "*", year = "*", info = "2nd Scheduled Timer") })
  private void scheduledTimeout2(final Timer t) {
    System.out.println(t.getInfo().toString() + " called at: "
        + new java.util.Date());
    System.out.println();
  }
}

As can be seen, the first timer is annotated with the @Schedule annotation. This annotation takes several parameters that define the timer schedule:

second	Number of seconds: 0 through 59
minute	Number of minutes: 0 through 59
hour	Number of hours: 0 through 23
dayOfWeek	Day of the week.  This can take textual values (Sun, Mon, Tue, Wed, Thu, Fri, Sat) or numerical values 0 through 7 (both 0 and 7 indicate Sunday)
dayOfMonth	Day of the month. This can take textual values (1st, 2nd etc), or numeric values 1 through 31. Negative values can also be used to indicate days before the end of the month. The value Last can also be used to indicate the last day of the month.
month	Month of the year. This can take textual values (Jan, Feb, Mar, Apr, May, Jun, Jul, Aug, Sep, Oct, Nov, Dec) or numerical values 1 through 12
year	The year. This can take numeric years in the format yyyy.
info	Additional information passed to the timer function.

The table above shows the allowable values that can be used for each expression used to build up a schedule. These values can also be expanded into expressions to make more complex schedules.

Wildcard: A wildcard character (*) is used to indicate that the schedule will fire for every valid value of the specific operand. For example, setting the value second="0", minute="*" would cause a timer to be invoked every minute at 0 seconds.

Lists: Comma separated lists of values allow timers to occur at every value in the list rather than at all valid values as specified by the wildcard character.  For example second="0", minute="0, 15, 30, 45" would cause a timer to be invoked every quarter of an hour.

Ranges: Hypen separated ranges allow timers to occur within the specified range.  For example dayOfMonth="1-5" would cause a timer to be invoked every day for the first 5 days of each month.

Intervals: Intervals are defined in the format start/interval and are valid only for hours, minutes and seconds.  An interval is defined as the start value for a timer and then the interval at which a timer will be invoked.  For example hour="12/1" would cause a timer to be invoked on the hour, every hour in an afternoon. It's possible to combine the wildcard and interval expressions to cause a timer to be invoked every x hours, minutes or seconds.  For example  minute="*/10" would cause a timer to be invoked every 10 minutes.

The second method in the example above shows how 2 different schedules can be applied to a timer.  In this instance, the method is annotated with the @Schedules annotation rather than the @Schedule annotation.