example/EchoService.java

import java.io.IOException;
import java.io.InputStream;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.net.ServerSocket;
import java.net.Socket;

class EchoService {

  public static void receive(int port) {
    try (ServerSocket sock = new ServerSocket(port)) {
      System.out.println("Listening on port " + port);
      while (!Thread.currentThread().isInterrupted()) {
        try (Socket client = sock.accept()) {
          InputStream inputStream = client.getInputStream();
          ObjectInputStream objectInputStream = new ObjectInputStream(inputStream);
          String msg = (String) objectInputStream.readObject();
          System.out.println("Received message " + msg);
          ObjectOutputStream objectOutputStream = new ObjectOutputStream(client.getOutputStream());
          objectOutputStream.writeObject(msg);
        }
      }
    } catch (IOException | ClassNotFoundException e) {
      e.printStackTrace();
      throw new IllegalStateException(e);
    }
  }

  public static void main(String[] args) {
    int port = Integer.parseInt(args[0]);
    receive(port);
  }

}