This week's book giveaway is in the OCPJP forum. We're giving away four copies of OCA/OCP Java SE 7 Programmer I & II Study Guide and have Kathy Sierra & Bert Bates on-line! See this thread for details.
Filters are used for pre-request processing and post-request processing logic.. So after pre-request processing logic has been completed a filter must ideally call chain.doFilter() this call will call the next filter or servlet in the chain. When the next element in the chain finishes it's processing, then the call to doFilter() returns. Then you can apply any post-request processing logic