Serveur TCP :

import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.PrintStream;
import java.net.ServerSocket;
import java.net.Socket;
 
public final class MainServer {
    static PrintStream out = System.out;
 
    public static void main(String[] args) throws ClassNotFoundException {
        int port = 8888;
 
        ServerSocket socket = null;
        try {
            // Création de la socket (en écoute sur le port 8888)
            socket = new ServerSocket(port);
        } catch (IOException e) {
            e.printStackTrace();
        }
 
        out.println("Listening on port " + port + "...");
 
        boolean running = true;
        Socket client = null;
 
        while (running) {
            try {
                // Attend la connexion d'un client
                client = socket.accept();
                out.println("New client...");
 
                // Flux d'entrée et sortie
                ObjectInputStream inputStream = new ObjectInputStream(
                        client.getInputStream());
                ObjectOutputStream outputStream = new ObjectOutputStream(
                        client.getOutputStream());
 
                // Lecture du message du client
                String message = (String) inputStream.readObject();
                out.println("Message from " + client.getInetAddress() + ": "
                        + message);
 
                // Traitement de la requête
                if (!message.equals("stop")) {
                    outputStream.writeObject("Yes, I'm alive!");
                } else {
                    running = false;
                    outputStream.writeObject("Ok, I'm shutting down.");
                }
 
                // Fermeture des flux
                inputStream.close();
                outputStream.close();
            } catch (IOException e) {
                e.printStackTrace();
            } finally {
                try {
                    // Fermeture de la connexion client
                    if (client != null) {
                        client.close();
                    }
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
 
        try {
            // Fermeture de la socket
            socket.close();
            out.println("Shutting down...");
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

Client TCP :

import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.PrintStream;
import java.net.Socket;
import java.net.UnknownHostException;
 
public final class MainClient {
    static PrintStream out = System.out;
 
    public static void main(String[] args) throws ClassNotFoundException {
        if (args.length != 2) {
            out.println("Usage: java MainClient [server address] [message]");
            System.exit(1);
        }
 
        Socket socket = null;
        try {
            // Connexion au serveur
            socket = new Socket(args[0], 8888);
 
            // Flux sortie
            ObjectOutputStream outputStream = new ObjectOutputStream(
                    socket.getOutputStream());
 
            // Envoi du message au serveur
            outputStream.writeObject(args[1]);
 
            // Flux d'entrée
            ObjectInputStream inputStream = new ObjectInputStream(
                    socket.getInputStream());
 
            // Lecture de la réponse
            String message = (String) inputStream.readObject();
            out.println("Response from " + socket.getInetAddress() + ": "
                    + message);
 
            // Fermeture des flux
            outputStream.close();
            inputStream.close();
        } catch (UnknownHostException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try {
                // Fermeture de la connexion réseau
                if (socket != null) {
                    socket.close();
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}