Get TimeZone offset value from TimeZone without TimeZone name

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I need to save the phone’s timezone in the format [+/-]hh:mm

No, you don’t. Offset on its own is not enough, you need to store the whole time zone name/id. For example I live in Oslo where my current offset is +02:00 but in winter (due to dst) it is +01:00. The exact switch between standard and summer time depends on factors you don’t want to explore.

So instead of storing + 02:00 (or should it be + 01:00?) I store "Europe/Oslo" in my database. Now I can restore full configuration using:

TimeZone tz = TimeZone.getTimeZone("Europe/Oslo")

Want to know what is my time zone offset today?

tz.getOffset(new Date().getTime()) / 1000 / 60   //yields +120 minutes

However the same in December:

Calendar christmas = new GregorianCalendar(2012, DECEMBER, 25);
tz.getOffset(christmas.getTimeInMillis()) / 1000 / 60   //yields +60 minutes

Enough to say: store time zone name or id and every time you want to display a date, check what is the current offset (today) rather than storing fixed value. You can use TimeZone.getAvailableIDs() to enumerate all supported timezone IDs.

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