Okutsu-san,

Thanks for your quick reply. I looked at the JDK-6380023. I think my point was slightly different - what I want to do is to create my own time zone and use it as default JRE's time zone. But, I agree that the things discussed in the bug are necessary to achieve my goal with java.util.TimeZone.

With JSR-310 changes, can we do this through ZoneRulesProvider SPI? Assume my goal is to support 'latest' rules from tz database, without waiting/updating time zone data update patch from Oracle (or others) - and use them in both traditional date/time APIs (Calendar/DateFormat) as well as java.time APIs. In this case, can I achieve the goal with -

1) Implement my own ZoneRulesProvider with a new unique zone id - e.g. "Boston-MA"
2) TimeZone.setDefault(TimeZone.getTimeZone("Boston-MA"))

With this approach, can I override the default time zone of the JRE, with all historic/future rule changes implemented by my custom zone "Boston-MA"?

-Yoshito

On 10/19/2014 8:03 PM, Masayoshi Okutsu wrote:
Hi Umaoka-san,

Thanks for your bug report which I've closed as a duplicate of JDK-6380023. Yes, it's an API design flaw of java.util.TimeZone.

Since we now have the java.time API, I guess JDK-6380023 doesn't have any high priority (unless it gets escalated by someone).

Regards,
Masayoshi

On 10/18/2014 5:43 AM, Yoshito Umaoka wrote:
Dear Java i18n team,

I was looking at recent Russian time zone changes and noticed a design issue in JDK. I think I knew this issue, but I forgot about this until recently. The problem is - Java does not support user defined custom TimeZone implementation properly.

java.util.TimeZone is quite old, and the original design assumed 'raw offset' and 'daylight saving amount' will never changed. To implement a subclass of TimeZone, you have to override an awkward abstract method - abstract int getOffset(int era, int year, int month, int day, int dayOfWeek, int milliseconds). This method signature itself does not limit a custom TimeZone implementation to support historic raw/dst offset changes. However, if you do so, you will see some problems in other places.

I filed a bug below:

====
Java should handle user defined TimeZone subclass instances supporting historic rule changes properly.

You can create a custom time zone implementation class by extending java.util.TimeZone. By the contract, the subclass must implement a few methods:

abstract int getOffset(int,int,int,int,int,int);
abstract int getRawOffset();
abstract boolean inDaylightTime(Date);
abstract void setRawOffset(int);
abstract boolean useDaylightTime();

Although, the interface above do not assume UTC offset or daylight saving amount is not changing time to time, a user can provide an implementation supporting historic UTC offset changes by int getOffset(int,int,int,int,int,int). However, there are two Java implementation problems.

1. The default implementation of TimeZone#getOffset(long date) does not use the abstract method - int getOffset(int,int,int,int,int,int). Therefore, when a different 'raw' offset was used in the past, or will be used in future, getOffset(long) always returns a result calculated from getRawOffset() and getDSTSavings(). Although a subclass implementation can provide TimeZone#getOffset(long date), the default implementation should use getOffset(int,int,int,int,int,int).

2. java.util.GregorianCalendar checks if a TimeZone instance is sun.util.calendar.TimZone or not, and if not, the offset field is calculated based on getRawOffset() / getDSTSavings(). Therefore, even a custom TimeZone implementation support different 'raw' offsets in the past or future, current 'raw' offset (getRawOffset()) value is used.


Use case:

A user may want to create a custom TimeZone instance from iCalendar VTIMEZONE component. iCalendr VTIMEZONE can support historic time zone rule changes.

Suggestions:

1) Add API TimeZone#getRawOffset(long) with the default implementation - return getRawOffset(). 2) Add API TimeZone#getDSTSavings(long) with the default implementation - return getDSTSavings(). 2) Update the default implementation of TimeZone#getOffset(long) to use #getRawOffset(long) #getDSTSavings(long) above along is existing #inDaylightTime(Date). 3) Gregorian calendar to use #getRawOffset(long) and #getDSTSavings(long), if not ZoneInfo.
====

There is an IETF working draft for timezone service protocol. In future, someone may want to create a custom time zone, interacting with a timezone service server to get the latest time zone rule data, instead of applying tzdata update utility. In this case, such limitation becomes a blocker. There are several ways to resolve the issue - I just suggested one way in the bug report. Are there anyone willing to look into this?

Thanks,
Yoshito



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