The file is empty(size =0) when down load from android device

public void download(HttpServletResponse response, InputStream attachObj){
   OutputStream os = response.getOutputStream();
   BufferedInputStream bis = null;
   try{
       response.setHeader("Pragma", "private");
       response.setHeader("Cache-Control", "private");
       response.setHeader("Expires", "-1");
       response.setContentType("application/octet-stream");
       response.setHeader("Content-Disposition", "attachment;" + "filename*=utf-8''" + filename);
       response.setHeader("Content-Length", filesize);
       bis = new BufferedInputStream(attachObj);
       int c;
       while ((c = bis.read()) != -1) {
           os.write(c);
       }
   }
   finally {
       os.flush();
       os.close();
       bis.close();
   }
}