In (at least what I would consider) a properly achitected web application, JSPs serve as presentation mechansims only. They perform no processing of their own except what is necessary for "display support". Such a
pattern is frequently refered to as "Model 2" or "MVC" or even "n-tiered". There has been much written on these subjects.
Inherently, when submitting a form, processing of the form data occurs. Such processing is inappropriate for a JSP in a web app following this pattern.
In fact, especially if you are using a JSP 2.0 container, it's better to write what have become termed "scriptless" JSP pages. That is: pages that contain no
java. No scriptlets, no declarations, no scriptlet expressions. Rather, these pages rely upon the EL (Expression Language), JSTL (JSP Standard Tag Library), JSP actions, and custom actions (formerly known as "custom tags") to perform their jobs.