title: Limit upload file action only for custom file extension using struts2
body: <p>I want to restrict the file upload action only for files with .key extension in Struts2. If I set filetype to <strong>application/octet-stream</strong> in fileUpload interceptor in struts.xml than it allows to upload all files with above content type without considering the extension but my requirement is to  limit the extension to <strong>.key</strong>.</p>