curl请求成功，Java HttpURLConnection却提示服务端接收参数null校验错误

需求背景：负责调用一个外部接口，请求方式为post，内容类型为x-www-form-urlencoded。

开发方式：测试驱动开发，使用curl验证接口，测试成功。主要是构造参数，完成测试后直接在代码中使用。

curl -X POST \
https://test.demo.com/msg/rest/send \
-H 'Authorization: manonxiaomai' \
-H 'Content-Type: application/x-www-form-urlencoded' \
-H 'cache-control: no-cache' \
-d 'timestamp=1621816295&&paramJson=%7B%22msgType%22%3A%22text%22%2C'

开发代码：使用Java HttpURLConnection进行url连接，然后使用OutputStream写出参数。

private static String createHttpReq(String urlStr, String data, String method) {
    URL url = null;
    HttpURLConnection conn = null;
    PrintWriter print = null;
    String result = "";
    try {
        url = new URL(urlStr);
        conn = (HttpURLConnection) url.openConnection();
        conn.setRequestProperty("Content-Type", "x-www-form-urlencoded;charset=utf-8");
        conn.setRequestProperty("Connection", "Keep-Alive");
        conn.setRequestProperty("cache-control", "no-cache");
        conn.setRequestProperty("Authorization", "manonxiaomai");
        conn.setConnectTimeout(3000);
        conn.setReadTimeout(3000);
        if ("post".equalsIgnoreCase(method)) {
            conn.setDoOutput(true);
            conn.setRequestMethod("POST");
            conn.setUseCaches(false);
        } else {
            conn.setRequestMethod("GET");
        }
        conn.setDoInput(true);
        conn.connect();
        if ("post".equalsIgnoreCase(method)) {
            print = new PrintWriter(conn.getOutputStream());
            print.print(data);
            print.flush();
        }
        BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(conn.getInputStream()));
        result = bufferedReader.readLine();
    } catch (Exception e) {
        e.printStackTrace();
    } finally {
        if (print != null) {
            try {
                print.close();
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }
    return result;
}

问题发现：Java程序运行后发现服务端返回参数为null的校验错误，怀疑是请求头信息不正确，仔细查看发现内容类型赋值不正确。

错误：conn.setRequestProperty("Content-Type", "x-www-form-urlencoded;charset=utf-8");
正确：conn.setRequestProperty("Content-Type", "application/x-www-form-urlencoded;charset=UTF-8");

解决办法：对于固定类型的值建议使用框架中自带的枚举值，或自己维护枚举值或常量，不要手写。