java HttpURLConnection 接口文件传输文件上传

public   String uploadImg(MultipartFile imgFile, String uploadUrl) throws  Exception {

        URL url = new URL(uploadUrl);
        HttpURLConnection conn = (HttpURLConnection) url.openConnection();
        conn.setConnectTimeout(10000);
        conn.setRequestMethod("POST");
        conn.setRequestProperty("Content-Type", "multipart/form-data; boundary=----123456789");
        conn.setDoInput(true);
        conn.setDoOutput(true);

        OutputStream os = new DataOutputStream(conn.getOutputStream());
        StringBuilder body = new StringBuilder();
        body.append("------123456789
");
        body.append("Content-Disposition: form-data; name='images'; filename='" + imgFile.getName() + "'
");

        //没有传入文件类型，同时根据文件获取不到类型，默认采用application/octet-stream
      String   contentType ="";
      String filename=imgFile.getName();
        //contentType非空采用filename匹配默认的图片类型
        if (filename.endsWith(".png")) {
            contentType = "image/png";
        }else if (filename.endsWith(".jpg") || filename.endsWith(".jpeg") || filename.endsWith(".jpe")) {
            contentType = "image/jpeg";
        }else if (filename.endsWith(".gif")) {
            contentType = "image/gif";
        }else if (filename.endsWith(".ico")) {
            contentType = "image/image/x-icon";
        }

        if (contentType == null || "".equals(contentType)) {
            contentType = "application/octet-stream";
        }

        body.append("Content-Type: "+contentType+"

");
        os.write(body.toString().getBytes());

            InputStream is =  imgFile.getInputStream();
            byte[] b = new byte[1024];
            int len = 0;
            while ((len = is.read(b)) != -1) {
                os.write(b, 0, len);
            }
            String end = "
------123456789--";
            os.write(end.getBytes());

            //输出返回结果
        BufferedReader br = new BufferedReader(new InputStreamReader(conn.getInputStream()));
        StringBuilder stringBuilder = new StringBuilder();
        String line = "";
        for (line = br.readLine(); line != null; line = br.readLine()) {

            stringBuilder.append(line);
        }
        return stringBuilder.toString();

   }