Hi All,
JDK displays incorrect TimeZone display name when DST (Daylight Saving
Time) is disable in the native Time Zone settings on Windows XP/2003
platforms and the Time Zone does not support DST.
Steps to re-create the problem
1. In the Windows Date and Time Properties dialog, set the time zone to
one that uses DST (e.g. Greenwich Mean Time).
2. Disable the 'Automatically adjust clock for Daylight Saving Changes'
option.
3. Change the time zone to one that does not use DST (e.g. India
Standard Time - (GMT+5:30) Chennai,Kolkata,Mumbai,New Delhi)
4. Compile and run the testcase[1]
Observed output:
GMT+05:30
Expected output:
India Standard Tim
There is already a sunbug[2] for this problem, which describes the
problem clearly and very detailed. Please refer it for more detail.
Here is some descriptions from the sunbug:
PROBLEM
---------------------------------
Windows provides an option entitled 'Automatically adjust clock for
Daylight Saving Changes' box in the native time zone settings. When
checked, the clock is automatically adjusted to the daylight savings
time if applicable to that particular timezone.
More importantly, if this box is unchecked, Windows will ignore any DST
timetable in the selected time zone.
Now, the JDK's TimeZone class checks the value of the registry value
that corresponds to this option, and modifies the default TimeZone's
display name accordingly. This is from the evaluation of CR 4296930,
describing the fix made for that CR in JDK 1.4.2:
--------
When the auto-adjustment is turned off, the platform time zone detection
code will create a time zone ID in the "GMT{+|-}hh:mm" form with which a
custom TimeZone customer is created. This is because some Windows users
turn it off due to incorrect Win32 time zones and choose one based on
just the GMT offset. A restriction is that display names are not
supported even it just means to use standard time of a correct time zone
selection for some other purposes.
--------
This makes sense for time zones that do use DST. However, our customers
have found that if you disable DST in the Windows options for a time
zone that uses it, and then switch to a time zone that doesn't use DST,
the option remains disabled (i.e. the underlying registry value retains
the value that corresponds to the option being disabled).
Under these circumstances the JDK's TimeZone class changes the display
name to the "GMT{+|-}hh:mm" format, rather than using the correct name.
This is unintuitive, and arguably incorrect.
We believe it would be better to query the time zone to see if DST is
actually applicable before deciding whether or not to switch to the
"GMT{+|-}hh:mm" format.
Note that this issue is not applicable to Windows Vista/7 because the
relevant registry value is reset each time the native time zone is
changed, rather than being retained as it is in Windows XP/2003.
I have made a fix which will deal with this situation and avoid the
"GMT{+|-}hh:mm" format.
[1] http://cr.openjdk.java.net/~littlee/ojdk-557/webrev.00/
<http://cr.openjdk.java.net/%7Elittlee/ojdk-557/webrev.00/>
[2] http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=7094176
Thanks a lot!
--
Best Regards,
Deven
