Parse and retrieve timezone offset from date-time

Question

Date format: \"yyyy-MM-dd\'T\'HH:mm:ss.SSSZ\"

Input date: \"2017-09-18T03:08:20.888+0200\"

Problem: I need retrieve timezon

Answer 1

SimpleDateFormat extends DateFormat and thus internally uses a Calendar. When parsing the date that calendar is being updated so you can get the timezone from it after parsing:

//use the timezone of the internally stored calendar
outputSdf.setTimeZone( inputSdf.getTimezone() );

That also shows why DateFormat is not threadsafe.

EDIT:

It seems the internal calendar's timezone isn't updated but the ZONE_OFFSET field is. Hence you could do something like this:

int zoneOffset = inputSdf.getCalendar().get( Calendar.ZONE_OFFSET );
//length check etc. left for you
String matchingZoneId = TimeZone.getAvailableIDs( zoneOffset )[0];
outputSdf.setTimeZone( TimeZone.getTimeZone( matchingZoneId ) );

Note that you can't just set the zone offset of the output format since that won't update the timezone reference which is used when formatting.

As you can see doing it this way looks a little "hacky" and thus you should think hard on whether you really need the timezone. In most cases you'd define the output timezone in a different way anyways, e.g. by getting the user's location, input, etc.