A working, simple to use Java Parser is... JavaParser. The project has been active for some years already. While it was initially hosted on Google code it is now available on GitHub: https://github.com/javaparser/javaparser
It is quite simple to use and the number of dependencies is small. It is also available on Maven.
It has been used for a few years, so it works quite well and permits to parse also comments, to change the AST and regenerate the code.
