Assign JavaScript variable to Java Variable in JSP

Java script plays on browser where java code is server side thing so you can't simply do this.

What you can do is submit the calculated variable from javascript to server by form-submission, or using URL parameter or using AJAX calls and then you can make it available on server

HTML

<input type="hidden" id="hiddenField"/>

make sure this fields lays under <form>

Javascript

document.getElementById("hiddenField").value=yourCalculatedVariable;

on server you would get this as a part of request

You need to read something about a JSP's lifecycle. Try this: http://en.wikipedia.org/wiki/File:JSPLife.png

JavaScript runs on the client, but in order to change the jsp, you need access to the server. This can be done through Ajax(http://en.wikipedia.org/wiki/Ajax_%28programming%29).

Here are some Ajax-related links: http://www.openjs.com/articles/ajax_xmlhttp_using_post.php

http://www.w3schools.com/ajax/tryit.asp?filename=tryajax_first