convert time from a different timezone other than local to GMT

Question

suppose i am a call center employee with IST time zone and want to fix a meeting with a US customer. I enquire about his time zone and time at which he will be available. Now i want to convert the time given by customer to my Timezones time. How can i do this in salesforce??

Answer 1

The Timezone class is new in Spring 13 and includes the getOffset() method to get

"the time zone offset, in milliseconds, of the specified date to the GMT time zone."

It should be possible to use this information to do the timezone conversion.

You would need a list of time zone ids. According to the docs these values match those in the Java TimeZone class. E.g. "America/Los_Angeles". Here is a good list of TimeZoneSidKeys - https://docs.google.com/spreadsheet/ccc?key=0Ar3Bg2QuV-_IdFNnbDdmOHpyV0NxQmhTUE5lN0hVLWc&hl=en#gid=0

Alternatively, you can see the valid values under the User Locale Settings > Time Zone.

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This is a bit rough, but it should give you a start. Here I convert a Date and Time from the users PST TimeZone to mine - NZDT.

// This is the Date and Time in the users TimeZone
string customerDateTimeString = '2013-02-17 17:35:00';
DateTime customerDateTime = DateTime.valueofGmt(customerDateTimeString);
string customerTimeZoneSidId = 'America/Los_Angeles';

TimeZone customerTimeZone = TimeZone.getTimeZone(customerTimeZoneSidId);
System.assertEquals('Pacific Standard Time',  customerTimeZone.getDisplayName());

integer offsetToCustomersTimeZone = customerTimeZone.getOffset(customerDateTime);
System.debug('GMT Offset: ' + offsetToCustomersTimeZone + ' (milliseconds) to PST');

// For the given Date I expect PST to be GMT - 8 hours
System.assertEquals(-8, offsetToCustomersTimeZone / (1000 * 60 *60));

// Here you might like to explicitly use 'Asia/Colombo' to get IST in your code.
TimeZone tz = UserInfo.getTimeZone();
// During daylight saving time for the Pacific/Auckland time zone
integer offsetToUserTimeZone = tz.getOffset(customerDateTime);
System.debug('GMT Offset: ' + offsetToUserTimeZone + ' (milliseconds) to NZDT');

// Expect NZDT to be GMT + 13 hours
System.assertEquals(13, offsetToUserTimeZone / (1000 * 60 *60));

// Figure out correct to go from Customers DateTime to GMT and then from GMT to Users TimeZone
integer correction = offsetToUserTimeZone - offsetToCustomersTimeZone;
System.debug('correction: ' + correction);

// Note: Potential issues for TimeZone differences less than a minute
DateTime correctedDateTime = customerDateTime.addMinutes(correction / (1000 * 60));
System.debug('correctedDateTime: ' + correctedDateTime);
// In the users Pacific/Auckland timezone the time should be moved forward 21 hours
System.assertEquals(correctedDateTime, DateTime.valueofGmt('2013-02-18 14:35:00'));

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Things might get a bit tricky around transitions to and from daylight savings in various regions. TimeZone.getOffset() will correct for this, but it would be worth creating some test cases for the boundary conditions.

Source xkcd