In our calendaring application, all times are stored as GMT based time.
When converting the GMT time to the local time, say to PST time, I
am using the following algorithm:
java.util.Calendar calendar = java.util.Calendar.getInstance();
calendar.setTimeZone(TimeZone.getTimeZone("GMT"));
calendar.set(year, month-1, date, hrs, min, sec);
return calendar.getTime();
However, the result is wrong when the time falls in the PST daylight
saving time zone.

The following test class shows the proble:

% cat test.java

import java.util.*;

public class test {

    public static void main(String args[]) {

if (args.length < 6) {
System.out.println("usage: java test year month date hour
min sec");
return;
}

Date date;
Calendar gmtcal = Calendar.getInstance();
gmtcal.setTimeZone(TimeZone.getTimeZone("GMT"));
gmtcal.set(Integer.parseInt(args[0]),
Integer.parseInt(args[1])-1,
Integer.parseInt(args[2]),
Integer.parseInt(args[3]),
Integer.parseInt(args[4]),
Integer.parseInt(args[5]));

date = gmtcal.getTime();
System.out.println("date = "+date);

Calendar cal = Calendar.getInstance();
cal.setTime(date);

int offset = cal.getTimeZone().getOffset(
cal.get(java.util.Calendar.ERA),
cal.get(java.util.Calendar.YEAR),
cal.get(java.util.Calendar.MONTH),
cal.get(java.util.Calendar.DATE),
cal.get(java.util.Calendar.DAY_OF_WEEK),
cal.get(java.util.Calendar.MILLISECOND));

System.out.println("offset for "+date+"= "+(offset/1000/60/60) + "hr");

    }

}

Sample output 1:
% /usr/local/java/jdk1.1.3/solaris/bin/java test 1997 1 1 12 0 0
date = Wed Jan 01 04:00:00 PST 1997
offset for Wed Jan 01 04:00:00 PST 1997= -8hr

Sample output 2:
% /usr/local/java/jdk1.1.3/solaris/bin/java test 1997 4 16 18 30 0
date = Wed Apr 16 10:30:00 PDT 1997
offset for Wed Apr 16 10:30:00 PDT 1997= -7hr

Note that in sample output 2 according to the offset, the gmt time
of the result would be 1997 4 16 17 30 0 which is different from the
input of 1997 4 16 18 30 0.

To work around the above problem, I use the following workaround to
do the conversion:

% cat testwkaround.java

import java.util.*;

public class testwkaround {

    public static void main(String args[]) {

if (args.length < 6) {
                System.out.println("usage: java testnewbug year month date hour
min sec");
                return;
        }

java.util.Calendar calendar = java.util.Calendar.getInstance();
        calendar.setTimeZone(TimeZone.getTimeZone("GMT"));
        calendar.set(Integer.parseInt(args[0]),
Integer.parseInt(args[1])-1,
Integer.parseInt(args[2]),
Integer.parseInt(args[3]),
Integer.parseInt(args[4]),
Integer.parseInt(args[5]));
        calendar.setTimeZone(TimeZone.getDefault());
 
        // get the timezone offset for the given date
        int offset = calendar.getTimeZone().getOffset(
                                calendar.get(java.util.Calendar.ERA),
                                calendar.get(java.util.Calendar.YEAR),
                                calendar.get(java.util.Calendar.MONTH),
                                calendar.get(java.util.Calendar.DATE),
                                calendar.get(java.util.Calendar.DAY_OF_WEEK),
                                calendar.get(java.util.Calendar.MILLISECOND));

        // adjust the date with calculated offset
        calendar.set(Integer.parseInt(args[0]),
Integer.parseInt(args[1])-1,
Integer.parseInt(args[2]),
Integer.parseInt(args[3]),
Integer.parseInt(args[4]),
Integer.parseInt(args[5]));
 
        // needed to make Calendar compute the time after set
        calendar.getTime();
        calendar.add(java.util.Calendar.MILLISECOND, offset);
 
        System.out.println("date = "+gmtcal.getTime());
    }
}

However, with the above workaround, the resulting time is off by
1 hr ahead/behind during the week when we transition into/out of DST
as shown by the following output:

% /usr/local/java/jdk1.1.3/solaris/bin/java testwkaround 1997 1 1 12 0 0
date = Wed Jan 01 04:00:00 PST 1997 <-- correct

% /usr/local/java/jdk1.1.3/solaris/bin/java testwkaround 1997 7 15 17 0 0
date = Tue Jul 15 10:00:00 PDT 1997 <-- correct

% /usr/local/java/jdk1.1.3/solaris/bin/java testwkaround 1997 4 6 18 30 0
date = Sun Apr 06 10:30:00 PDT 1997 <-- 1hr ahead of correct time of
11:30am

% /usr/local/java/jdk1.1.3/solaris/bin/java testwkaround 1997 10 27 17 0 0
date = Mon Oct 27 10:00:00 PST 1997 <-- 1hr behind correct time of
9:00 am