http://www.javafr.com/codes/PRAYER-ALERT-SALA_40601.aspx
hello, it’s not a library but a student project. But quite well executed.
Or : http://www.directionsmag.com/article.php?article_id=2956
A method to calcul prayer time with google map+local time ( in short : check where you are, check how far your are from the Makkah , apply the right formula )