参考网址：https://www.cnblogs.com/duelsol/p/5128271.html

    try {
            //创建连接 
            URL url = new URL(url);
            HttpURLConnection connection = (HttpURLConnection) url.openConnection();
            connection.setDoOutput(true);
            connection.setDoInput(true);
            connection.setRequestMethod("POST");
            connection.setUseCaches(false);
            connection.setInstanceFollowRedirects(true);
            connection.setRequestProperty("Content-Type", "application/json");
            connection.connect();
            // POST请求 
            DataOutputStream out = new                     
            DataOutputStream(connection.getOutputStream());
            JSONObject obj = new JSONObject();
            String json = java.net.URLEncoder.encode(obj.toString(), "utf-8");
            out.writeBytes(json);
            out.flush();
            out.close();
            // 读取响应 
            BufferedReader reader = new BufferedReader(new 
            InputStreamReader(connection.getInputStream()));
            String lines;
            StringBuffer sb = new StringBuffer("");
            while ((lines = reader.readLine()) != null) {
                lines = URLDecoder.decode(lines, "utf-8");
                sb.append(lines);
            }
            System.out.println(sb);
            reader.close();
            // 断开连接 
            connection.disconnect(); 
        } catch (MalformedURLException e) { 
            e.printStackTrace(); 
        } catch (UnsupportedEncodingException e) { 
            e.printStackTrace(); 
        } catch (IOException e) { 
            e.printStackTrace(); 
        }