package ip2019;

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.net.InetAddress;
import java.net.ServerSocket;
import java.net.Socket;
import java.io.DataOutputStream;

public class Server {

    private ServerSocket server;

    public Server(String ipAddress) throws Exception {
        int port = 1234;
        if (ipAddress != null && !ipAddress.isEmpty())
          this.server = new ServerSocket(port, 1, InetAddress.getByName(ipAddress));
        else
          this.server = new ServerSocket(port, 1, InetAddress.getLocalHost());
    }

    void listen() throws Exception {
        String data = null;
        Socket client = this.server.accept();
        String clientAddress = client.getInetAddress().getHostAddress();
        System.out.println("\r\nNew connection from " + clientAddress);

        BufferedReader in = new BufferedReader(
                new InputStreamReader(client.getInputStream()));
        DataOutputStream dos = new DataOutputStream(
                client.getOutputStream());

        while ( (data = in.readLine()) != null ) {
            System.out.println("\r\nMessage from " + clientAddress + ": " + data);
            dos.writeBytes(data);
            System.out.println("Message sent to the client is "+ data);
        }
    }

    public InetAddress getSocketAddress() {
        return this.server.getInetAddress();
    }

    public int getPort() {
        return this.server.getLocalPort();
    }


}

------------------------------------------------------------------

package ip2019;

public class Main {
    public static void main(String[] args) throws Exception {

        String adress = "127.0.0.1";
        String port = "1234";

        Server server = new Server(adress);

        System.out.println("\r\nRunning Server: " +
                "Host=" + server.getSocketAddress().getHostAddress() +
                " Port=" + server.getPort());

        server.listen();
    }
}

------------------------------------------------------------------

package ip2019_client;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.InetAddress;
import java.net.Socket;
import java.util.Scanner;

public class Client {
    protected Socket socket;
    private Scanner scanner;
    private BufferedReader is = null;

    protected Client(InetAddress serverAddress, int serverPort) throws Exception {
        this.socket = new Socket(serverAddress, serverPort);
        this.is = new BufferedReader(new InputStreamReader(
                this.socket.getInputStream()));
        this.scanner = new Scanner(System.in);
    }

    protected void start() throws IOException, InterruptedException {
        String input;

        while (true) {
            input = scanner.nextLine();
            PrintWriter out = new PrintWriter(this.socket.getOutputStream(), true);
            out.println(input);
            out.flush();

            Thread.sleep(1000);
            System.out.println("waiting for server return");

            String responseLine = is.readLine();
            System.out.println("Server returns: " + responseLine);
        }
    }
}

------------------------------------------------------------------

package ip2019_client;

import java.net.InetAddress;

public class Main_client {
    public static void main(String[] args) throws Exception {
        String adress = "127.0.0.1";
        String port = "1234";

        Client client = new Client(
                InetAddress.getByName(adress),
                Integer.parseInt(port));

        System.out.println("\r\nConnected to Server: " + client.socket.getInetAddress());
        client.start();
    }
}