URLDecoder 可以直接用java里面的工具包，如果不行，从源码里拷贝URLDecoder 和URLEncoder两个类 ，并引入。

    @Autowired
    private URLDecoder urlDecoder;

接口代码：

    @GetMapping("/downloadPact/{url}")
    @ApiOperation(value = "下载", notes = "下载", httpMethod = "GET")
    public void downloadPact(@PathVariable(value = "url") String urlParam, HttpServletResponse response) throws IOException {
        String url= urlDecoder.decode(urlParam,"UTF-8");
        HttpURLConnection conn = null;
        try {
            File file = new File(url);
            // 取得文件的后缀名。
            String ext = file.getName().substring(file.getName().lastIndexOf(".") + 1).toLowerCase();
            StringBuffer buffername = new StringBuffer(url.substring(url.lastIndexOf("/")+1));

            String filename = buffername.toString();

            URL path = new URL(url);
            conn = (HttpURLConnection) path.openConnection();
            conn.setRequestMethod("GET");
            conn.setConnectTimeout(5 * 1000);
            InputStream fis = conn.getInputStream();// 通过输入流获取数据

            byte[] buffer = readInputStream(fis);
            if (null != buffer && buffer.length > 0) {
                // 清空response
                response.reset();
                // 设置response的Header
                response.addHeader("Content-Disposition", "attachment;filename=" + new String((filename).getBytes("GBK"), "ISO8859_1"));
                response.addHeader("Content-Length", "" + buffer.length);
                OutputStream toClient = response.getOutputStream();
                response.setContentType("application/octet-stream");
                toClient.write(buffer);
                toClient.flush();
                toClient.close();
            }

        } catch (IOException ex) {
            ex.printStackTrace();
        } finally {
            if (conn != null) {
                conn.disconnect();
            }
        }

    }

如果是Post请求，

@PostMapping("/downloadSubsPact")
@ApiOperation(value = "下载", notes = "下载", httpMethod = "Post")
public void downloadSubscribPact(@RequestParam(value = "url") String url, HttpServletResponse response) throws IOException {

输入流：

  /**
     * 从输入流中获取数据
     * @return
     * @throws Exception
     */
    private byte[] readInputStream(InputStream fis) throws IOException {
        ByteArrayOutputStream outStream = new ByteArrayOutputStream();
        byte[] buffer = new byte[1024];
        int len = 0;
        while( (len=fis.read(buffer)) != -1 ){
            outStream.write(buffer, 0, len);
        }
        fis.close();
        return outStream.toByteArray();
    }