private boolean isPortUsing(final int port) {
        boolean flag = false;
        try (Socket socket = new Socket(InetAddress.getByName("127.0.0.1"), port)) {
            flag = true;
        } catch (Exception ignored) {

        }
        return flag;
    }
Ture is use else false.

@param port server port
@return boolean
shenyu-plugin/shenyu-plugin-proxy/shenyu-plugin-mqtt/src/main/java/org/apache/shenyu/plugin/mqtt/handler/MqttPluginDataHandler.java