I don't know whether Netbean have this kind of problem or this only happen to Eclipse IDE. Whenever there are jars that required to be link in the project, make sure all these jars are located under WEB-INF/lib folder. Although the build path has already been configure, or you don't even configure your project's build path, I don't care. I don't care whatever reason you have, always remember that you are wrong.
As long as the WEB-INF/lib contains the jars require, it just work. I strongly highlight this to those who are new in web development. Please jot it down!