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.
While you could use a filter for server-side anything, including validation, I don't think it's a good idea. Filters are best used for purposes that are orthogonal to the servlets that will be running. In other words, if the servlets depend upon the filter being run in order to execute properly, such as with the validation idea, then what good is it to take that logic out of the servlet and put it in a filter? There are much better ways to share common code (if that's the idea behind it).
even i do not know, but i just want to know, my scenario is that if server side validation gives any error message we are supposed to send a notification or a message to client some times technical staff and sometimes to the server.
Filters are good for "out of band" things like authentication, or setting no-cache headers. They should not be used for doing "in-line" things that are better and easier to handle in the servlet itself.