Here's a class for calculating an approximate time of the sunset, sunrise and day length on a given date, on a given location (latitude coordinate). It takes into account leap years and daylight saving time offset.
It's accurate to about 20 minutes (compared to results from WolframAlpha).

Also, because the constructor Date(int year, int month, int day) is marked as deprecated, GregorianCalendar class is used instead.

Main article:
http://dev.kafol.net/2012/09/java-calculating-approximate-sunset-and.html