find user OS using Spring-mvc / tomcat

How can I find my user's OS in my web app, using Spring-mvc framework ?

I assume I can scan the user-agent value, but is there any existing solution/lib ? (there is so much possible values for each os...)

Thanks 开发者_C百科

JavaScript can do a browser and OS detection. Use it to initialize a hidden field which is submitted through some form or sent to the server using AJAX.