I am not talking about my application. I refered that example http://www.mkyong.com/struts2/struts-2-file-upload-example/ which you suggested.
I refered whole example .That worked very nice.But when i try to add this line only
String filePath = servletRequest.getSession().getServletContext().getRealPath("/"); in action class.I got 404 error.
But ,now that example working with the above line also.
I did small mistake in struts.xml ie i didn't add <interceptor-ref name="basicStack"></interceptor-ref> .
When i added this line , my new app was working and file uploaded in server also.
action in struts.xml file:
Thanks Swastik for your help.