Often you encounter ClassNotFoundException. Most of the times, just looking at the stack trace will give you idea about which jar file you have to add to your build path. What if you can’t find?, check javacio.us. All you need to do it subscribe to their service though your Google account. They also provide other Java related links on top of your Google search. But I think finding jar files is the most interesting feature and it came to my rescue couple of times. Check more about it here.(If you like these kind of tools, also check GotAPI).