How to make Date locale-independent?

Question

I have a db, that stores dates in OleDateTime format, in GMT timezone. I've implemented a class, extending Date in java to represent that in classic date format. But my class is locale-dependent (I'm in GMT+2). Therefore, it converts the date in the db as date - 2 hours. How do I make it convert the date correctly? I want my class to be locale-independent, always using GMT timezone. Actually, the question is:

class MyOleDateTime extends Date {

    static {
        Locale.setDefault(WhatGoesHere?)
    }

    // ... some constructors
    // ... some methods
}

Answer 1

Well, it's better to use the Calendar object like suggested in other answers. However, if you really want to set global timezone, you can use TimeZone.setDefault(TimeZone.getTimeZone("UTC")); early in your application code. There is also user.timezone Java system property.

Also (just fun to know), it appears that the only country actually living by GMT/UTC time (without daylight saving changes) is Liberia.

In fact, Date objects per se are always locale- and timezone-independent. Its getTime() method will always return the number of milliseconds passed since January 1, 1970 00:00:00 (not counting leap seconds) in UTC. But if you want to get something else than milliseconds, you have to use Calendar, which is timezone-dependent. But it is the right way to go. You don't use that deprecated methods in Date class, do you?

Answer 2

As Michael Borgwardt has already said, the Java Date object does not know anything about timezones. It's just a wrapper for a number of milliseconds since 01-01-1970 00:00:00 UTC.

You start dealing with timezones only when you for example convert the Date object to a String using a DateFormat. You set the timezone on the DateFormat to specify in which timezone you want to see the Date.

DateFormat df = new SimpleDateFormat("dd-MM-yyyy HH:mm:ss Z");
df.setTimeZone(TimeZone.getTimeZone("UTC"));

String text = df.format(date);  // text will contain date represented in UTC