[jboss-user] [Management, JMX/JBoss] - Re: org.jboss.varia.scheduler.Scheduler Problem ?

[jaikiran]

"FDomino" wrote :  but its strange
  | that it looks like that the schedulePeriod is just added.... and not maybe converted... 
  | 
  | <attribute name="SchedulePeriod">86400000</attribute>
  | 
  | 

Though i haven't completely seen how its behaving on your system (i mean at what "time" the timer is triggered), i think i know what the problem is.

The problem lies in the value being passed to SchedulePeriod. 86400000 milli seconds form 1 day. But on the day when the DST is applied, adding 86400000 to the time is not equivalent to adding 1 day to the date. Here's an example - I have access to a system hosted in US (Pacific Standard Time). This year (2008) the daylight saving time began on March 9 at 2 AM.  So in our example, lets start with the date as March 9, 1 AM. The example below, 

- first adds 86400000 milli seconds to March 9, 1 AM.  The intention is to get the output date as March 10, 1 AM.  However as you see in the output, that i have posted below, the output date is Mar 10, 2 AM. Which is not what i wanted.

- Later, instead of adding 86400000 milli seconds, i add 1 day using Calendar.DATE, to the original date  March 9, 1 AM. Again, the intention is to get output date as March 10, 1 AM. As shown in the output, this works. So because of the DST, 1 day is not equal to 86400000 milli seconds on March 9.

There's a way to figure out the offset in milliseconds because of the DST. So when adding the  86400000 milli seconds to increment by a day, you should take into account, this offset. See my comments in the code below which does this. When this offset is considered,  the output date is as expected March 10, 1 AM.


  | package org.myapp;
  | 
  | import java.text.DateFormat;
  | import java.text.ParseException;
  | import java.text.SimpleDateFormat;
  | import java.util.Calendar;
  | import java.util.Date;
  | import java.util.GregorianCalendar;
  | import java.util.Properties;
  | import java.util.TimeZone;
  | 
  | public class DateUtility {
  | 
  |     /**
  |      * @param args
  |      */
  |     public static void main(String[] args) {
  |         try {
  | 
  |         	Calendar calendar = new GregorianCalendar();
  |         	TimeZone tz = calendar.getTimeZone();
  |         	System.out.println("Timezone is " + tz.getDisplayName());
  |         	System.out.println("Amount of time to be added because of DST  " + tz.getDSTSavings() + " milli sec");
  |         	DateFormat df1 = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss.SSS");
  | 
  |             Date originalDate = df1.parse("2008-03-09 01:00:00.000");
  |             calendar.setTime(originalDate);
  |             System.out.println("Original date is " + calendar.getTime());
  | 
  | 		// Jaikiran: Adding 86400000 milli seconds to increment by one day
  | 		// does NOT work
  | 		// Add 86400000 milli seconds and display the output
  |             calendar.add(Calendar.MILLISECOND,86400000);
  |             System.out.println("Date after adding 86400000 milli sec to original date is " + calendar.getTime());
  | 
  |             // Reset to original date
  |             calendar.setTime(originalDate);
  | 
  | 		// Jaikiran: Adding 1 day through Calendar.DATE works
  |             // Now add 1 day and display the output
  | 		calendar.add(Calendar.DATE,1);
  |             System.out.println("Date after adding 1 day to original date is " + calendar.getTime());
  | 
  |             // Reset to original date
  |             calendar.setTime(originalDate);
  | 
  | 		// Jaikiran: Take into consideration the DST offset and then add the milli seconds.
  | 		// This works.
  |             // Now add (86400000 milli seconds - tz.getDSTSavings() ) and display the output
  |             calendar.add(Calendar.MILLISECOND,86400000 - tz.getDSTSavings());
  |             System.out.println("Date after adding (86400000-" + tz.getDSTSavings() + ") = " + (86400000 - tz.getDSTSavings()) + " milli sec to original date is " + calendar.getTime());
  | 
  | 
  | 		} catch (Exception e) {
  | 			e.printStackTrace();
  | 		}
  | 	}
  | 
  | }
  | 

The output of this code:

Timezone is Pacific Standard Time
  | Amount of time to be added because of DST  3600000 milli sec
  | Original date is Sun Mar 09 01:00:00 PST 2008
  | Date after adding 86400000 milli sec to original date is Mon Mar 10 02:00:00 PDT 2008
  | Date after adding 1 day to original date is Mon Mar 10 01:00:00 PDT 2008
  | Date after adding (86400000-3600000) = 82800000 milli sec to original date is Mon Mar 10 01:00:00 PDT 2008
  | 


So to handle this efficiently, either 

- The org.jboss.varia.scheduler.Scheduler should be enhanced to accept a string value like "DAILY" for the SchedulePeriod attribute. This will shield the user from passing the correct milli seconds value for a day. 

OR

- The user who configures the scheduler xml, should be smart enough to know the effect of DST and then decide what value to pass to the SchedulePeriod.




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