Question

I cannot use Joda. When I try to create a Date or Calendar from a String representing a date or datetime in UTC, the resulting object has a timezone associated with it…

Here’s the code:

Case 1:

SimpleDateFormat sdf = new SimpleDateFormat("yyyyDDD");
sdf.setTimeZone(TimeZone.getTimeZone("UTC"));
Date date = sdf.parse("2012018");
Calendar cal = new GregorianCalendar(TimeZone.getTimeZone("UTC"));
cal.setTime(date);
System.out.println(cal.getTime()); //Tue Jan 17 19:00:00 EST 2012 !?!*&#&??

Case 2:

SimpleDateFormat sdf = new SimpleDateFormat("yyMMddHHmm");
sdf.setTimeZone(TimeZone.getTimeZone("UTC"));
Date date = sdf.parse("1202011431");
Calendar cal = new GregorianCalendar(TimeZone.getTimeZone("UTC"));
cal.setTime(date);
System.out.println(cal.getTime()); //Wed Feb 01 09:31:00 EST 2012 !?!*&#&??

Answer 1

Objects of type java.util.Date are an absolute amount of time since Epoch. When you create a Date object from a Calendar, it loses any TimeZone that the Calendar may have been using and just gives you a raw quantity of time. EST isn’t really ‘associated’ with your Date, it’s just that the toString method on Date uses the JVM default timezone to create a human readable representation.

It’s important to understand that the usage of Calendar in the above code samples is doing absolutely nothing. Changing just the timezone like that changes only the human readable representation of that Calendar. The raw number of milliseconds since epoch is the same before and after you call setTime and getTime.

(All of the methods on java.util.Date that are related to human readable representations are deprecated and do not work properly, it is best to simply pretend they do not exist.)