Calculating time for different timezone, problems with daylight savings?

Question

Hi all,
I try to convert my locale time to a different timezone (like a world clock does). This worked until Europe got "summer time". Then my time calculation went wrong. I just paste the following coding to give you a quick reproducable code.
I did a lot of googleing but nothing found so far. Also search here in the forum didn't help me solving it. So now I created a post on my own.
The output of the Java programm is the following (without the colored comments). I just entered these comments to show you where the calculation is right and where it goes wrong.
I have absolutely now idea about where the chase the error. I am only guessing with "daylight savings issue".
Hopefully anybody has a good idea.
Thanks in advance
John
Europe/London {color:#339966} *(correct calculation!)*{color}
daylight shift in millis: 3600000
Is in daylight savings: true
19.04.2010 11:28:53
*Europe/Berlin {color:#339966}(correct calculation){color}*
daylight shift in millis: 3600000
Is in daylight savings: true
19.04.2010 12:28:53
Australia/Sydney{color:#ff0000} (wrong calculation, shoul 1 hour){color}
daylight shift in millis: 3600000
Is in daylight savings: false
*19.04.2010 20:28:53*
America/New_York {color:#339966}(correct calculation){color}
daylight shift in millis: 3600000
Is in daylight savings: true
19.04.2010 06:28:53
Asia/Bangkok {color:#ff0000}(wrong calculation, shoud 1 hour){color}
daylight shift in millis: 0
Is in daylight savings: false
19.04.2010 17:28:53
Asia/Hong_Kong {color:#339966}(correct calculation){color}
daylight shift in millis: 0
Is in daylight savings: false
19.04.2010 18:28:53
package test.timezone;
import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.GregorianCalendar;
import java.util.LinkedList;
import java.util.List;
import java.util.TimeZone;
public class TZCalc {
public static void main(String[] args) {
List<TimeZone> list = new LinkedList<TimeZone>();
list.add(TimeZone.getTimeZone("Europe/London"));
list.add(TimeZone.getTimeZone("Europe/Berlin"));
list.add(TimeZone.getTimeZone("Australia/Sydney"));
list.add(TimeZone.getTimeZone("America/New_York"));
list.add(TimeZone.getTimeZone("Asia/Bangkok"));
list.add(TimeZone.getTimeZone("Asia/Hong_Kong"));
for (TimeZone tz : list) {
Calendar cal = new GregorianCalendar(tz);
SimpleDateFormat formatter = (SimpleDateFormat) DateFormat
.getDateTimeInstance(DateFormat.MEDIUM, DateFormat.MEDIUM);
formatter.setTimeZone(tz);
System.out.println("\n"  +tz.getID());
System.out.println("daylight shift in millis: "  tz.getDSTSavings());
System.out.println("Is in daylight savings: "  tz.inDaylightTime(cal.getTime()));
System.out.println(formatter.format(cal.getTime()));
}Edited by: jbegham on Apr 19, 2010 3:46 AM
Edited by: jbegham on Apr 19, 2010 3:47 AM

Answer 1

You should not set the time zone on the calendar since you want the calendar based on UTC.
        List<TimeZone> list = new LinkedList<TimeZone>();
        list.add(TimeZone.getTimeZone("Europe/London"));
        list.add(TimeZone.getTimeZone("Europe/Berlin"));
        list.add(TimeZone.getTimeZone("Australia/Sydney"));
        list.add(TimeZone.getTimeZone("America/New_York"));
        list.add(TimeZone.getTimeZone("Asia/Bangkok"));
        list.add(TimeZone.getTimeZone("Asia/Hong_Kong"));
        Calendar cal = new GregorianCalendar(); // Regardless of your timezone this holds the number of milliseconds since 1/1/1970 UTC.
        for (TimeZone tz : list)
            SimpleDateFormat formatter = (SimpleDateFormat) DateFormat.getDateTimeInstance(DateFormat.MEDIUM, DateFormat.MEDIUM);
            formatter.setTimeZone(tz);
            System.out.println("\n" + tz.getID());
            System.out.println("daylight shift in millis: " + tz.getDSTSavings());
            System.out.println("Is in daylight savings: " + tz.inDaylightTime(cal.getTime()));
            System.out.println(formatter.format(cal.getTime()));
        } I have no idea whether or not this then gives the results you expect.