Convert UTC Time T0 Local Time In Java or Groovy

Question

i need to store createdOn (One Of the Attribute in Domain Class) . i am getting the system time and storing the value for this attribute.. My Time zone is (GMT+5:30 Chennai, Kolkata,Mumbai, New Delhi ) when i upload to the server it stores UTC time . I want it to be IST (Indian Standard Time) My Application Uses Groovy on Grails. Please Help me to adjust UTC /IST Time Difference. Thanks In advance

Answer 1

No, don't do that. Ever!

If you store times in local form, you're in for a world of pain. You basically have to store both the local time and the local timezone and the display of the time then becomes a complex beast (working out the source and target timezones).

All times should be stored as UTC. No exception. Times entered by a user should be converted to UTC before being written anywhere (as soon as possible).

Times to be shown to a user should be converted from UTC to local as late as possible.

Take this advice from someone who once got bogged down in the multi-timezone quagmire. Using UTC and converting only when necessary will make your life a lot easier.

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Once you have the UTC time, it's a matter of using the SimpleDateFormat class to convert it:

import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.TimeZone;

public class scratch {
    public static void main (String args[]) {
        Date now = new Date();
        SimpleDateFormat sdf = new SimpleDateFormat ("yyyy-MM-dd HH:mm:ss");
        sdf.setTimeZone (TimeZone.getTimeZone ("IST"));
        System.out.println ("Time in IST is " + sdf.format (now));
    }
}

This outputs:

Time in IST is 2011-04-11 13:40:04

which concurs with the current time in Mirzapur, which I think is where IST is based (not that it matters in India at the moment since it only has one timezone).

Answer 2

        SimpleDateFormat sf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        sf.setTimeZone(TimeZone.getTimeZone("GMT"));
        System.out.println(sf.format(new Date()));


        SimpleDateFormat sf1 = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        sf1.setTimeZone(TimeZone.getTimeZone("Asia/Calcutta"));
        System.out.println(sf1.format(new Date()));
        System.out.println(Arrays.asList(TimeZone.getDefault()));