Best way would be to use Struts, or a simple controller servlet to
which the JSP submits. The servlet (or action servlet in case of
struts) can process data if request.getMethod() is "post", or it can
redirect to the form if the method is "get". While processing, you can
choose to put the logic in the servlet (not a good idea) or have the
servlet call some other class to handle the logic, once the servlet has
extracted and validated the form data coming in.

-cheers,
Manish