How do I create a client-server socket communication?

In this example you’ll see how to create a client-server socket communication. The example below consist of two main classes, the ServerSocketExample and the ClientSocketExample. The server application listen to port 7777 at the localhost. When we send a message from the client application the server receive the message and send a reply to the client application.

The communication in this example using the TCP socket, it means that there is a fixed connection line between the client application and the server application.

package org.kodejava.example.net;

import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.lang.ClassNotFoundException;
import java.lang.Runnable;
import java.lang.Thread;
import java.net.ServerSocket;
import java.net.Socket;

public class ServerSocketExample {
    private ServerSocket server;
    private int port = 7777;

    public ServerSocketExample() {
        try {
            server = new ServerSocket(port);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    public static void main(String[] args) {
        ServerSocketExample example = new ServerSocketExample();
        example.handleConnection();
    }

    public void handleConnection() {
        System.out.println("Waiting for client message...");

        //
        // The server do a loop here to accept all connection initiated by the
        // client application.
        //
        while (true) {
            try {
                Socket socket = server.accept();
                new ConnectionHandler(socket);
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}

class ConnectionHandler implements Runnable {
    private Socket socket;

    public ConnectionHandler(Socket socket) {
        this.socket = socket;

        Thread t = new Thread(this);
        t.start();
    }

    public void run() {
        try
        {
            //
            // Read a message sent by client application
            //
            ObjectInputStream ois = new ObjectInputStream(socket.getInputStream());
            String message = (String) ois.readObject();
            System.out.println("Message Received: " + message);

            //
            // Send a response information to the client application
            //
            ObjectOutputStream oos = new ObjectOutputStream(socket.getOutputStream());
            oos.writeObject("Hi...");

            ois.close();
            oos.close();
            socket.close();

            System.out.println("Waiting for client message...");
        } catch (IOException e) {
            e.printStackTrace();
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
    }
}
package org.kodejava.example.net;

import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.lang.ClassNotFoundException;
import java.net.InetAddress;
import java.net.Socket;
import java.net.UnknownHostException;

public class ClientSocketExample {
    public static void main(String[] args) {
        try {
            //
            // Create a connection to the server socket on the server application
            //
            InetAddress host = InetAddress.getLocalHost();
            Socket socket = new Socket(host.getHostName(), 7777);

            //
            // Send a message to the client application
            //
            ObjectOutputStream oos = new ObjectOutputStream(socket.getOutputStream());
            oos.writeObject("Hello There...");

            //
            // Read and display the response message sent by server application
            //
            ObjectInputStream ois = new ObjectInputStream(socket.getInputStream());
            String message = (String) ois.readObject();
            System.out.println("Message: " + message);

            ois.close();
            oos.close();
        } catch (UnknownHostException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
    }
}

To test the application you need to start the server application. Each time you run the client application it will send a message “Hello There…” and in turns the server reply with a message “Hi…”.

Wayan Saryada

A programmer, a slow runner, a recreational open water diver, currently living in the island of Bali, Indonesia. Mostly programming in Java, creating web based application with Spring Framework, JPA, etc. If you need help on Java programming you can hire me on Fiverr.

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