How can I prevent XSS attacks in a JSP/Servlet web application?
The how-to-prevent-xss has been asked several times. You will find a lot of information in StackOverflow. Also, OWASP website has an XSS prevention cheat sheet that you should go through.
On the libraries to use, OWASP's ESAPI library has a java flavour. You should try that out. Besides that, every framework that you use has some protection against XSS. Again, OWASP website has information on most popular frameworks, so I would recommend going through their site.