// TEST OK
// 參考 https://crunchify.com/in-java-jow-to-check-if-socket-is-alive-and-connection-is-active-on-specific-port-issocketalive-utility/

    private static boolean testConn(String hostName, int port)

    {

        boolean isAlive = false;



        SocketAddress socketAddress = new InetSocketAddress(hostName, port);

        Socket socket = new Socket();


        // 單位:milliseconds

        int timeout = 3000; //3,000 ms = 3 sec


        try {

            socket.connect(socketAddress, timeout);

            //socket.close();

            isAlive = true;


        } catch (SocketTimeoutException exception) {

            System.out.println("testConn SocketTimeoutException " + hostName + ":" + port + ". " + exception.getMessage());

        } catch (IOException exception) {

            System.out.println(

                    "testConn IOException - Unable to connect to " + hostName + ":" + port + ". " + exception.getMessage());

        }finally{

            try {

                socket.close();

            } catch (IOException e) {

                System.out.println("testConn socket close fail");

            }

        }

        return isAlive;

    }