Confirming Quartz Trigger firing times (especially cron expressions)

The Quartz Scheduler is very useful when it comes to scheduling jobs. It offers a wide range of trigger options, including cron-like expressions. Cron-like expressions are a bit obscure to read, unless you use them often. These expressions are explained in the CronExpression and CronTrigger classes API, and in the online tutorial. I sometimes need to make sure that the triggers will get fired at the proper time. The TriggerUtils class allows to output all firing dates of a trigger between two dates : TriggerUtils#computeFireTimesBetween(Trigger, Calendar, Date, Date). The Calendar parameter here is not a java.util.Calendar, but a org.quartz.Calendar, which can be annoying when using both java.util.Calendar and org.quartz.Calendar in the same class.

Making a sample program to output all firing times between two dates is rather simple :

import java.text.ParseException;
import java.util.List;

import org.quartz.CronTrigger;
import org.quartz.Trigger;
import org.quartz.TriggerUtils;
import org.quartz.impl.calendar.AnnualCalendar;


public class ConfirmTriggerFireTimes {

 public static void main(String[] args) throws ParseException {
  new ConfirmTriggerFireTimes().showTriggerFireTimes();
 }
 
 public void showTriggerFireTimes() throws ParseException {
  CronTrigger trigger = new CronTrigger();
  // Fire at 10:15am every Monday, Tuesday, Wednesday, and Thursday 
  trigger.setCronExpression("0 15 10 ? * MON-THU");
  java.util.Calendar startDate = java.util.Calendar.getInstance();
  startDate.set(2011,java.util.Calendar.JANUARY, 1);
  java.util.Calendar endDate = java.util.Calendar.getInstance();
  endDate.set(2011,java.util.Calendar.JANUARY, 31);
  outputFireTimeList(trigger, startDate, endDate);
 }
 
 @SuppressWarnings("rawtypes")
 private void outputFireTimeList(Trigger trigger, java.util.Calendar from, java.util.Calendar to) {
  List fireTimeList = TriggerUtils.computeFireTimesBetween(trigger, null, from.getTime(), to.getTime());
  for ( int i = 0; i < fireTimeList.size(); i++ ) {
   System.out.println(fireTimeList.get(i));
  }
 }
}

In this example, I want to confirm the firing dates of a trigger set to fire at 10:15am every Monday, Tuesday, Wednesday, and Thursday in January. The resulting output is :

Mon Jan 03 10:15:00 JST 2011
Tue Jan 04 10:15:00 JST 2011
Wed Jan 05 10:15:00 JST 2011
Thu Jan 06 10:15:00 JST 2011
Mon Jan 10 10:15:00 JST 2011
Tue Jan 11 10:15:00 JST 2011
Wed Jan 12 10:15:00 JST 2011
Thu Jan 13 10:15:00 JST 2011
Mon Jan 17 10:15:00 JST 2011
Tue Jan 18 10:15:00 JST 2011
Wed Jan 19 10:15:00 JST 2011
Thu Jan 20 10:15:00 JST 2011
Mon Jan 24 10:15:00 JST 2011
Tue Jan 25 10:15:00 JST 2011
Wed Jan 26 10:15:00 JST 2011
Thu Jan 27 10:15:00 JST 2011
Mon Jan 31 10:15:00 JST 2011

This looks good. We can see that any jobs associated to this trigger will be executed at 10:15am every Monday, Tuesday, Wednesday, and Thursday.