/**
  * 附件下载
  * <p>
  *
  * @param param
  * @return ResponseDTO
  */
 @PostMapping(value = "/download")
 public void downloadFile(@RequestParam Map<String, Object> param, HttpServletResponse response) throws Exception {
  String url1 = param.get("url").toString();
  URL url = new URL(url1);
  URLConnection conn = url.openConnection();
  InputStream inputStream = conn.getInputStream();
  response.reset();
  response.setContentType(conn.getContentType());
   //纯下载方式 文件名应该编码成UTF-8
  response.setHeader("Content-Disposition",
    "attachment; filename=" + URLEncoder.encode(param.get("name").toString(), "UTF-8"));
  byte[] buffer = new byte[1024];
  int len;
  OutputStream outputStream = response.getOutputStream();
  while ((len = inputStream.read(buffer)) > 0) {
   outputStream.write(buffer, 0, len);
  }
  inputStream.close();
 }

//下载和预览
  handlePreview(file) {
  if (file.type == 'png' || file.type == 'jpg') {
   this.imageUrl = file.url;
   this.imageDetail = true;
  } else {
   var form = document.createElement("form");
   document.body.appendChild(form);
   form.method = "post";
   form.appendChild(this.generateHideElement('url',file.url));
   form.appendChild(this.generateHideElement('name',file.name));
   form.action = "接口地址"// 路由地址+接口地址
   form.submit();
  }
  },
  generateHideElement(name, value) {
  var tempInput = document.createElement("input");
  tempInput.type = "hidden";
  tempInput.name = name;
  tempInput.value = value;
  return tempInput;
  },