Java Examples - How do I create a client-server socket communication?

How do I create a client-server socket communication?

Category: java.net, viewed: 140K time(s).

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...".