Have you added the FileUpload library to the runtime classpath? Keep in mind that the runtime classpath is different from the compile-time classpath - it consists of the WEB-INF/classes and WEB-INF/lib directories of the web app in question.
If you are getting the exception copy both commons_io.jar and commons_file_upload.jar files to the WEB_INF/lib folder of the war file in the app/web server.
[size=12]It should work. Some IDE s don't automatically put the jar files in the library path to the deployment war files in the server.[/size]