Issue in calculating time diff between DST & Non-DST time

[Rajagopal Mani]

Hello Rangers,

System need to show time diff in UI between 2 dates.

E.g.
Date1 -> Meeting start time(Possibly any timezone date) -> Getting this date from external source
Date2 -> Current time of the meeting location -> Finding current time based on concern time zone id

Both date is base lined with GMT and manipulate the time diff. This approach is working fine if both dates fall under same period(DST or Non-DST)

E.g. Issue scenario

Date1 -> Nov-3 6AM (Non-DST)
Date2 -> Nov-3 1AM (DST)

Vice-versa as well...

Note : Server & Desktop can be located in any timezone

Surfing to obtain posible solutions. Even found similar thread with subject "java.util.Calendar, setTime and DST" in this forum itself but couldnt get properly

There would be effective ways to calculate the time diff to handle all the scenarios. Really appreciable if anybody suggest on this.

Thanks in advance

- Raj

[Campbell Ritchie]

You need the concept that Date does not encapsulate a date. It encapsulates how many milliseconds have elapsed since 1st January 1970. Does that information help you?

SimpleDateFormat format = new SimpleDateFormat("dd/MMM/yyyy hh:mm:ss z");
Date d1 = format.parse("12/Mar/2012 12:34:56 GMT");
Date d2 = format.parse("14/May/2013 07:30:00 EST");
long difference = d2.getTime() - d1.getTime();

…and if that code works I shall be very surprised!

[Winston Gutkowski]

Rajagopal Mani wrote:There would be effective ways to calculate the time diff to handle all the scenarios. Really appreciable if anybody suggest on this.

In addition to Campbell's wise words, have a look at ABriefHistoryOfJavaTime. Hopefully, it will give you all the information you need.

And if not, come back and tell us what you don't understand.

Winston

[Rajagopal Mani]

First of all thank you both..

Have gone thru the link. Really useful in which my understanding some what narrowed down on java time.

With this, have come up with a way. below the psuedo code. please correct me if anything wrong in it

Date d1 = new Date(date1.getTime() - tz.getOffset(date1));
Date d2 = new Date(date2.getTime() - tz.getOffset(date2));

SimpleDateFormat format = new SimpleDateFormat("dd/MMM/yyyy hh:mm:ss z");

Date fd1 = format.parse(d1);
Date fd2 = format.parse(d2);

long timeDiff = fd1.getTime() - fd2.getTime();

- Raj

[Winston Gutkowski]

Rajagopal Mani wrote:With this, have come up with a way. below the psuedo code. please correct me if anything wrong in it

I'm sorry if this sounds harsh but, based on your original post, just about everything is wrong with the first part of your code.

Java Dates ALL have the same start point, so no conversion is required whatsoever and you DON'T need to convert them to Strings.
The interval is simply:
Math.abs( d1.getTime() - d2.getTime() );

If, on the other hand, your input "dates" are strings, then the second part of your code (from line 4 on) is very close to being correct, except that 'd1' and 'd2' will be Strings, not Dates.

Simple rule: DON'T change Java times. It's almost always wrong.

HIH

Winston

[Rajagopal Mani]

Yes conversion to string not required. flaw there..

Below two ways would give proper time diff to show in any location irrespective of the sever locations or time zones. Out of two ways, without baseline with GMT would be more efficient than other until dates provides proper milliseconds from epoch. please correct if anything wrong here & suggest if anymore best.

public class TimeDiff {

	public TimeDiff() {
		Date mst = null; // Receiving meeting start time date from external source
		getTimeDiffWayOne(mst);
		getTimeDiffWayTwo(mst);
	}
	
	private String getTimeDiffWayOne(Date mst) {
		String st_tzID = null; // Time zone ID of meeting start time. can get it from internal DB using location code
		TimeZone tz1 = TimeZone.getTimeZone(st_tzID);
		
		Date meetingStartTime = new Date(mst.getTime() - tz1.getOffset(mst.getTime()));
		
		String ct_tzID = null; // Time zone ID of current time. can get it from internal DB using location code
		TimeZone tz2 = TimeZone.getTimeZone(ct_tzID);
		Calendar cal = Calendar.getInstance(tz2);
		Date currentTime = new Date(cal.getTime().getTime() - tz2.getOffset(cal.getTime().getTime()));
		
		return getTimeDiff(meetingStartTime, currentTime);
	}

	private String getTimeDiffWayTwo(Date mst) {
		String ct_tzID = null; // Time zone ID of current time
		TimeZone tz2 = TimeZone.getTimeZone(ct_tzID);
		Date currentTime = Calendar.getInstance(tz2).getTime();
		
		return getTimeDiff(mst, currentTime);
	}
	
	private String getTimeDiff(Date st, Date ct) {
        String diff = "";
        long timeDiff = Math.abs(st.getTime() - ct.getTime());
        diff = String.format("%d : %d", TimeUnit.MILLISECONDS.toHours(timeDiff),
                TimeUnit.MILLISECONDS.toMinutes(timeDiff) - TimeUnit.HOURS.toMinutes(TimeUnit.MILLISECONDS.toHours(timeDiff)));
        return diff;
	}

	public static void main(String[] args) {
		new TimeDiff();
	}
}

Thanks
-Raj

[Rajagopal Mani]

Hi,

Please correct if any concern in above approaches

Thanks,
Raj