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Re: Possible to treat time in milliseconds as a different time zone?

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Tue, 21 May 2013 07:58:28 -0700 (PDT), /laredotornado@zipmail.com/:

> I'm using Java 6.  I'm trying to see if there's a simple way to
> convert a long varaible (the number of milliseconds since 1970)
> to a timezone other than GMT.  I have another time zone string,
> MY_TIMEZONE, which could be a timezone string ("GMT-5"), but I'm
> figuring out this doesn't work ...
>
>      long timeInMs = 1368921600000;
>      final Calendar cal = Calendar.getInstance();
>      cal.setTimeZone(TimeZone.getTimeZone(MY_TIMEZONE));
>      cal.setTimeInMillis(timeInMs);
>      final java.util.Date dateObj = cal.getTime();
>      System.out.println(dateObj.toString());
>
> Can I parse the time zone string to get the number of hours
> difference and then just add that?  Grateful for any elegant
> solutions.  Thanks, - Dave

What do you expect when you say "convert"?

As others have pointed out the java.util.Date type is a simple 
wrapper for a timestamp value which is always in UTC.  If you 
initialize a java.util.Calendar instance and set its timeZone - 
you've already converted it in a way.  When you query the Calendar 
fields HOUR_OF_DAY, MINUTE, etc. you've got your conversion.  You 
may use these values to initialize your custom type of time object, 
also.

If you want to _format_ a time/timestamp in a text representation 
using specific time-zone, instead, you may use a java.util.DateFormat:

     final String MY_TIMEZONE = "JST";
     long timeInMs = 1368921600000L;
     DateFormat dateFormat = DateFormat.getDateTimeInstance();
     System.out.println(dateFormat.format(new Date(timeInMs)));
     dateFormat.setTimeZone(TimeZone.getTimeZone(MY_TIMEZONE));
     System.out.println(dateFormat.format(new Date(timeInMs)));

Note, your example code does really nothing to the Calendar.time 
value, even if you change the Calendar's timeZone in between:

     long timeInMs = 1368921600000L;
     Calendar cal = Calendar.getInstance();
     cal.setTimeZone(TimeZone.getTimeZone(MY_TIMEZONE));
     cal.setTimeInMillis(timeInMs);
     java.util.Date dateObj = cal.getTime();
     cal.setTimeZone(TimeZone.getTimeZone(MY_TIMEZONE2));
     java.util.Date dateObj2 = cal.getTime();
     System.out.println(dateObj.getTime() == dateObj2.getTime());

-- 
Stanimir

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Possible to treat time in milliseconds as a different time zone? laredotornado@zipmail.com - 2013-05-21 07:58 -0700
  Re: Possible to treat time in milliseconds as a different time zone? Arne Vajhøj <arne@vajhoej.dk> - 2013-05-21 11:23 -0400
  Re: Possible to treat time in milliseconds as a different time zone? Eric Sosman <esosman@comcast-dot-net.invalid> - 2013-05-21 11:31 -0400
  Re: Possible to treat time in milliseconds as a different time zone? Stanimir Stamenkov <s7an10@netscape.net> - 2013-05-21 23:09 +0300
  Re: Possible to treat time in milliseconds as a different time zone? Nigel Wade <nmw@ion.le.ac.uk> - 2013-05-22 10:00 +0100
    Re: Possible to treat time in milliseconds as a different time zone? Jukka Lahtinen <jtfjdehf@hotmail.com.invalid> - 2013-05-22 13:08 +0300
      Re: Possible to treat time in milliseconds as a different time zone? Daniele Futtorovic <da.futt.news@laposte-dot-net.invalid> - 2013-05-22 16:46 +0200
  Re: Possible to treat time in milliseconds as a different time zone? Roedy Green <see_website@mindprod.com.invalid> - 2013-05-22 03:03 -0700
  Re: Possible to treat time in milliseconds as a different time zone? Robert Klemme <shortcutter@googlemail.com> - 2013-05-26 14:23 +0200
  Re: Possible to treat time in milliseconds as a different time zone? Michal Kleczek <michal_wytnijto@kleczek.org> - 2013-05-27 11:45 +0200

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