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<a href="/download"> 点击下载 </a>

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@RequestMapping (value="/download")
public String downloads (HttpServletResponse response ,HttpServletRequest request) throws Exception {
   // 要下载的图片地址
   String  path = request.getServletContext ().getRealPath ("/upload");
   String  fileName = "基础语法.jpg";

   //1、设置 response 响应头
   response.reset (); // 设置页面不缓存，清空 buffer
   response.setCharacterEncoding ("UTF-8"); // 字符编码
   response.setContentType ("multipart/form-data"); // 二进制传输数据
   // 设置响应头
   response.setHeader ("Content-Disposition",
           "attachment;fileName="+URLEncoder.encode (fileName, "UTF-8"));

   File file = new File (path,fileName);
   //2、 读取文件 -- 输入流
   InputStream input = new FileInputStream (file);
   //3、 写出文件 -- 输出流
   OutputStream out = response.getOutputStream ();

   byte [] buff =new byte [1024];
   int index=0;
   //4、执行 写出操作
   while ((index= input.read (buff))!= -1){
       out.write (buff, 0, index);
       out.flush ();
  }
   out.close ();
   input.close ();
   return null;
}