Hi,
Probably the easiest solution here is to do it the "right way": HTTPS.
Just get a certificate (which, quite frankly, *any* solution to a
problem like this should include, to prevent man-in-the-middle
attacks), and configure your server to use SSL. Bingo. All form data
is transmitted encrypted from the user's browser to the server and is
decrypted before it even gets to your JSP. As an added bonus, the
request URLs and other headers as well as the entire response are
encrypted (maybe not necessary in your case, but certainly harmless).
Any decent web server should already include SSL (i.e. Apache's
mod_ssl and so on).

Chris