Here is one link I felt it was really useful. I have seen lots of projects has these lots of commons jars in classpath. But it is surprising that we seldom use it in our code. Mostly we are re inventing some common utility methods. So, as Java developers it will be good if we learn the utility methods in commons then we will bring them in practice. How to use Commons? Here is the link that will teach us do so, http://www.discursive.com/books/cjcook/reference/book-cjcook.html This site also allows us to download the PDF. It would ask us to register. For those willing to download can click this link. Coomons cookbook Happy commons!