This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori on-line! See this thread for details.
Yes..filters can be used to make wrappers.This is because you might want to compress the response you are getting from a servlet and you can create your own custom response object and pass it as a parameter to the chain.doFilter(req,res) method.
For details of this please refer to HFSJ book.It has been explained beautifully there.Though you do not need to know it in detail.