SOS...从数据库读取二进制数据下载文件出现乱码的问题

Question

public void doGet(HttpServletRequest request, HttpServletResponse response) throws
      ServletException, IOException
  {
    response.setContentType(CONTENT_TYPE);
    PrintWriter out = response.getWriter();    Conn co = new Conn();
    DBcon con = new DBcon(co.getcon());
    ResultSet rs = null;    response.reset(); 
    response.setContentType("text/plain");     OutputStream output = null;
    InputStream input = null;
    try
    {
      rs = con.doSelect("select pic from aa where id=2");
      if (rs.next())
      {
        input = rs.getBinaryStream("pic");
      }      String filenamedisplay = "test.txt"; 
      filenamedisplay = URLEncoder.encode(filenamedisplay, "UTF-8");
      response.addHeader("Content-Disposition",
                         "attachment;filename=" + filenamedisplay);      output = response.getOutputStream();
      byte[] b = new byte[1024];
      int i = 0;
      while ( (i = input.read(b)) > 0)
      {
        output.write(b, 0, i);
      }      output.flush();
    }
    catch (Exception e)
    {
      System.out.println("Error!");
      e.printStackTrace();
    }
    finally
    {
      if (input!= null)
      {
        input.close();
        // input= null;
      }
      if (output != null)
      {
        output.close();
        //output = null;
      }
    }  }
如题，请高手指教!