Unless if you use a Webservice, sending data back to form from the Servlet may not possible.
Once the form submits the data to the Servlet, the connection will be lost between the form and Servlet.
But if you use a Webservice, you can trap the response and display it to the user.
Other alternative to Servlet approach is, display a another page in the browser with the response.
So the user after submits will be notified of the result in a new window.
Thanks
Srini