How can I convert from Gregorian Calendar to Unix Time, in Java?

Question

I am in need of a method to convert GregorianCalendar Object to Unix Time (i.e. a long). Also need a method to convert Unix Time (long) back to GregorianCalendar Object. Are there any methods out there that does this? If not, then how can I do it? Any help would be highly appreciated.

Link to GregorianCalendar Class --> http://download.oracle.com/javase/1.4.2/docs/api/java/util/GregorianCalendar.html

Thanks.

Answer 1

The methods getTimeInMillis() and setTimeInMillis(long) will let you get and set the time in milliseconds, which is the unix time multiplied by 1000. You will have to adjust manually since unix time does not include milliseconds - only seconds.

long unixTime = gregCal.getTimeInMillis() / 1000;
gregCal.setTimeInMillis(unixTime * 1000);

Aside: If you use dates a lot in your application, especially if you are converting dates or using multiple time zones, I would highly recommend using the JodaTime library. It is very complete and quite a bit more natural to understand than the Calendar system that comes with Java.