Question

I have a GMT field in which the user enter a time to be converted to IST (for eg: in hour field 18, minute field 30, in session field am/pm). I need to get those inputs and convert to IST in java???

Answer 1

This is very easy and obvious if you realize that the timezone is only relevant for a date formatted as String – second/millisecond timestamps (of which java.util.Date is merely a wrapper) are always implicitly UTC (what GMT is properly called). And converting between such a timestamp and a string always uses a timezone, both ways.

So this is what you need to do:

    DateFormat utcFormat = new SimpleDateFormat(patternString);
    utcFormat.setTimeZone(TimeZone.getTimeZone("UTC"));
    DateFormat indianFormat = new SimpleDateFormat(patternString);
    indianFormat .setTimeZone(TimeZone.getTimeZone("Asia/Kolkata"));
    Date timestamp = utcFormat.parse(inputString);
    String output = indianFormat.format(timestamp);