Dates in Java

[Harry Singh]

Hi All,

I'm having problems converting GMT date time to other timezone formats. Basically I can convert the date time but it doesnt take into effect the day light saving time. I'm doing something like this.

         //Convert the string to proper GMT DATE TIME
         String strDateTime = "20081022020310Z";
         DateFormat formatter = new SimpleDateFormat("yyyyMMddHHmmss");
         formatter.setTimeZone(TimeZone.getTimeZone("GMT"));
         Date gmtDate = 
            (Date)formatter.parse
                   (idmDateTime.substring(0,strDateTime.length()-1));
         System.out.println("----------------- GMT");
         System.out.println("... " + formatter.format(gmtDate.getTime()) 
                                   +   " is GMT Date time.");
 
         //Convert it to Australian East time
          Calendar localDateTime = new  
           GregorianCalendar(TimeZone.getTimeZone(("Australia/Sydney")));
           DateFormat localDateTimeformatter = new   
                      SimpleDateFormat("dd/MMM/yyyy HH:mm:ss");
    
           localDateTimeformatter.setTimeZone
                      (TimeZone.getTimeZone("Australia/Sydney"));
           localDateTime.setTimeInMillis(gmtDate.getTime());
 
           System.out.println("----------------- LOCAL");
           System.out.println("... " +  
           localDateTimeformatter.format(localDateTime.getTime()) + " is  
                                                  Local Date time.");
 

This code works fine. However It should return GMT+ 11 time in Australian tiem due to day light savings. But it just gives me back GMT+ 10. Any pointers as to how to fix this problem?

Thanks in advance,
Harry

[Mark Vedder]

What version (including patch level) of Java are you using?

I noticed on the alldownunder.com Daylight Saving Time page that there was a change for DST in 2008 in Australia. DST will start on the first Sunday in October. In the past, it was apparently the last Sunday in October. We went through a similar change here in the US a year or two ago.

So older versions (i.e. patch levels) of Java will not have the change. You'd have to do some digging through the release notes to see which patches to 1.4.2, 1.5 and 1.6 contain the change.

My curiosity was peeked, so I wrote a quick little program to loop through October. It prints out the GMT time and Sydney time, and the result of TimeZone.inDaylightTime(Date). When I ran the code, I received GMT+11 for the date you had above (22 Oct 2008). (I changed the GMT time to midnight so my tired brain could to the time offset calculation easier ) Notice the DST change occurs as its suppose to on 5 October 2008:

 
For 03 Oct  Is in daylightSavingsTime: false
GMT: 03/Oct/2008 00:03:10
Aus: 03/Oct/2008 10:03:10
For 04 Oct  Is in daylightSavingsTime: false
GMT: 04/Oct/2008 00:03:10
Aus: 04/Oct/2008 10:03:10
For 05 Oct  Is in daylightSavingsTime: true
GMT: 05/Oct/2008 00:03:10
Aus: 05/Oct/2008 11:03:10
For 06 Oct  Is in daylightSavingsTime: true
GMT: 06/Oct/2008 00:03:10
Aus: 06/Oct/2008 11:03:10
 
. . .
 
For 22 Oct  Is in daylightSavingsTime: true
GMT: 22/Oct/2008 00:03:10
Aus: 22/Oct/2008 11:03:10
 

The last date (22 Oct 2008) is the one you showed in your code.

This was run via Java 1.6.0_07. I also ran it against 1.5.0_16 and got the same results. (I didn't run it against a 1.4.2 version, but the latest patch would probably be ok.)

When I ran it against the older Java 1.6.0 and 1.5.0_11, I got very different results:

For 03 Oct  Is in daylightSavingsTime: false
GMT: 03/Oct/2008 00:03:10
Aus: 03/Oct/2008 10:03:10
For 04 Oct  Is in daylightSavingsTime: false
GMT: 04/Oct/2008 00:03:10
Aus: 04/Oct/2008 10:03:10
For 05 Oct  Is in daylightSavingsTime: false
GMT: 05/Oct/2008 00:03:10
Aus: 05/Oct/2008 10:03:10
For 06 Oct  Is in daylightSavingsTime: false
GMT: 06/Oct/2008 00:03:10
Aus: 06/Oct/2008 10:03:10
. . .
For 22 Oct  Is in daylightSavingsTime: false
GMT: 22/Oct/2008 00:03:10
Aus: 22/Oct/2008 10:03:10
. . .
For 25 Oct  Is in daylightSavingsTime: false
GMT: 25/Oct/2008 00:03:10
Aus: 25/Oct/2008 10:03:10
For 26 Oct  Is in daylightSavingsTime: true
GMT: 26/Oct/2008 00:03:10
Aus: 26/Oct/2008 11:03:10

So those versions are still using the old rule of "last Sunday in October" to calculate when DST starts. Again, you'll need to check the release notes to see at what patch level the new DST rule was introduced for each version.

I hope that helps.
[ August 19, 2008: Message edited by: Mark Vedder ]

[Harry Singh]

Thanks Mark for your inputs.

Indeed this was the problem. I noticed that may be I will have to apply a patch to make this DST change to happen in Java.