How to validate GET/POST parameter to avoid javascript injection

I'm building an AJAX enabl开发者_开发问答ed web application in which I'm accepting to inputs from user or sometimes building query string based on user action.

Using firebug or other tools anyone can inspect and view data being sent to server.

I would like to know how to validate query variables at server side using java to detect malicious script being sent to server.

Thanks.