Thanks to CodeProject Answers for replying my questions.
Now I have a problem on the file upload with Struts2 & Sitemesh.
I'm using Struts2.3.8 and Sitemesh 3.
I'm using Sitemesh's filter between StrutsPrepareFilter and StrutsExecuteFilter so that struts2 feactures( such as properties of action classes ) could be accessed on sitemesh decorator pages.
Then the problem is that submitted file is not stored on struts2 action value stack.
If I remove sitemesh filter then fiel upload is successfully done.
Why this happens?