This sort of problem is precisely why the concept of "sessions" was invented. Look up HttpSession in your servlet books/websites, and
you should find lots of examples of gathering or chacking information in one servlet and using it in another.
Even if your pages are generated by a single servlet (not usually a good idea, unless you delegate to other classes or templates), you should still store your information in the session to make sure that your system still works when more than one person tries to access it at once.