This is just one of the example programs I tried out that I really liked. It is a simple echo server. It receives a message from a client, then sends that message back. Here is the code:

package simpleserver;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.ServerSocket;
import java.net.Socket;
import java.io.PrintWriter;

/**
 *
 * @author bacpeters
 */
public class SimpleServer {

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        if (args.length < 1) {
            System.err.println("Usage: java SimpleServer <port number>");
            System.exit(0);
        }
        
        int portNumber = Integer.parseInt(args[0]);
        
        System.out.println("Listening for client on port: " + portNumber);
        
        try (ServerSocket serverSocket = new ServerSocket(portNumber);
            Socket clientSocket = serverSocket.accept();
            PrintWriter out = new PrintWriter(clientSocket.getOutputStream(), true);
            BufferedReader in = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));) {
            
            System.out.println("Client connected on port: " + portNumber);
            
            String inputLine;
            
            while ((inputLine = in.readLine()) != null) {
                System.out.println("Received message: " + inputLine);
                out.println("Back at ya: " + inputLine);
            }
            in.close();
            out.close();
            
        } catch (IOException e) {
            System.out.println(e);
        }
    }
    
}

In the Project Properties, Run category, I configure the desired port number to be passed into the program when I hit “Run”:

After starting the program, I connect to the server via Terminal using Telnet:

telnet <ip> <port>

Then I just type a message and wait to receive the echoed response.

To get started with socket programming with Java 8, start here.