頁面寫法：

<a href="http://localhost:8080/download">下載檔案</a>

java 服務的寫法：

@RequestMapping( value = "/download", method = RequestMethod.GET )
public void testDownload( HttpServletResponse res ) {
    String fileName = "upload.jpg";

    res.setHeader("content-type", "application/octet-stream");
    res.setContentType("application/octet-stream");
    res.setHeader("Content-Disposition", "attachment; filename=" + fileName);
    byte[] buff = new byte[1024];
    BufferedInputStream bis = null;
    OutputStream os = null;

    try {
      os = res.getOutputStream();
      bis = new BufferedInputStream(new FileInputStream( 
                new File("d://" + fileName )));
      int i = bis.read(buff);

      while (i != -1) {
        os.write(buff, 0, buff.length);
        os.flush();
        i = bis.read(buff);
      }
    } catch ( IOException e ) {
      e.printStackTrace();
    } finally {
      if (bis != null) {
        try {
          bis.close();
        } catch (IOException e) {
          e.printStackTrace();
        }
      }
    }
    System.out.println("export file finish");
  }
}