import java.net.*;
import java.io.*;

public class EchoServer {
  public static void main(String[] args) throws IOException {
    
    if (args.length != 1) {
      System.err.println("Usage: java EchoServer <port number>");
      System.exit(1);
    }
    
    int portNumber = Integer.parseInt(args[0]);
    
    try (
      ServerSocket serverSocket = new ServerSocket();
    ) {
      serverSocket.bind(new InetSocketAddress("localhost", Integer.parseInt(args[0]) ) );
      try (
        Socket clientSocket = serverSocket.accept();        
        PrintWriter out = new PrintWriter(clientSocket.getOutputStream(), true);           
        BufferedReader in = new BufferedReader( new InputStreamReader(clientSocket.getInputStream()));
      ) {
      // no catch here
        System.out.println("Connected to "+clientSocket.getInetAddress().toString()+":"+clientSocket.getPort());
        String inputLine;
        while ((inputLine = in.readLine()) != null) {
          out.println(inputLine);
          System.out.println("echoing: "+inputLine);
        }
      } catch (IOException e) {
        System.out.println("Exception caught when trying to listen on port "
          + portNumber + " or listening for a connection");
        System.out.println(e.getMessage());
      }
    }
  }
}