Java - getting consistent UTC values irrespective of server

Question

I am work on a version of a product which will be used by the users in India and am working from India (GMT+5:30). Our Servers are in US. Some scheme is to be applied which has a start date and end date (eg - From Aug 01, 00:00:00 to Aug 31 11:59:59 it must be active). Am using http://www.ruddwire.com/handy-code/date-to-millisecond-calculators/ for I used this code assuming getTime will have a consistent UTC time-

// dateStr is what user enters on UI like 1/08/2013 format = dd/MM/yyyy
public static long getUTCDateWithFormat(String dateStr, String format) throws ParseException {
    SimpleDateFormat sdf = new SimpleDateFormat(format);
    Date date = sdf.parse(dateStr);
    return date.getTime();
}

So considering start time, when I run from localhost, For August 1, I got result = 1375295400000, which means Thu Aug 01 2013 00:00:00 GMT+0530 (India Standard Time). (So I understand there is a 5 hrs 30mins milliseconds to be subtracted from the UTC since at runtime I have to compare system time with this value.)

Expected similar UTC to be saved when run from server (US), but it saved 1375336800000 which means Thu Aug 01 2013 11:30:00 GMT+0530 (India Standard Time) so UTC time is different and there is 11:30 hours flaw in addition to 5:30 hrs flaw.

Did not use the following code on the server but I expect similar results -

Calendar calendar = Calendar.getInstance();
String[] arr = dateStr.split("/");
calendar.set(new Integer(arr[2]), new Integer(arr[0]), new Integer(
        arr[1]));
return calendar.getTime();

Kindly help me resolve this problem. Also while doing comparison at runtime I have to use new Date() so how should that be?

Answer 1

Is the problem the fact that you want to see the current time in UTC milliseconds on both server and client at the same time? If this is the case calling System.currentTimeMillis() should return the same value (both in the US and India if called at the same time).

If that's not it, maybe you might want to pass a timezone into the GregorianCalendar, like this:

GregorianCalendar cal1 = new GregorianCalendar(TimeZone.getTimeZone("US/Pacific"))

Maybe you can detail the problem a bit if it persists?

Answer 2

java.util.Date has a number of problems and should be avoided. You should instead be using java.util.Calendar, and probably the specific calendar java.util.GregorianCalendar. The Calendars are much better behaved in terms of consistency, and do not depend on the operating system functionality/details.

So, start using Gregorian Calendars.