after 19 posts you should have figured out by now that people are not going to do your homework for you. Research java and xpath yourself and see what kind of libraries can help you. Try to write some code first and if you get stuck, post what you have done and people can guide you.
I will at least give you a nudge. If you are completely new to Java and XML, I would look into the SAX parser. Using it you can learn how to parse an XML document at the lowest level and really get a feel for it. From there you can go to the next step of using DOM and Xpath.