我用java写了一段文件下载代码，最后下载的时候发现了一个古怪的问题，在线求指导！

try
  {
   request.setCharacterEncoding("utf-8");
   response.setCharacterEncoding("utf-8");                  
   String name=request.getParameter("name");
   String fname=request.getParameter("filename");
   System.out.println(name+"文件名");
   System.out.println(fname+"文件夹");      String webpath=request.getSession().getServletContext().getRealPath("")+"/"+"manage_file"+"/"+"public_space/";
      String savePath=webpath+fname;
           response.setContentType("application/x-download");
          String filenamedownload = savePath + "/" + name;
       String filenamedisplay = name;
          
     filenamedisplay = URLEncoder.encode(filenamedisplay, "UTF-8");
     response.setHeader("Content-Disposition", "attachment;filename="+ filenamedisplay);
     try {
      OutputStream os = response.getOutputStream();
      FileInputStream fis = new FileInputStream(filenamedownload);
      byte[] b = new byte[1024];
      int i = 0;
      while ((i = fis.read(b)) > 0) {
       os.write(b, 0, i);
      }
      fis.close();
      os.flush();
      os.close();
     } 
     catch (Exception e) 
     {
      e.printStackTrace();
     }
  }
  catch(Exception e)
  {
   e.printStackTrace();
  }