mport 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(Integer.parseInt(args[0]));
      Socket clientSocket = serverSocket.accept();   
      PrintWriter out =
        new PrintWriter(clientSocket.getOutputStream(), true);           
      BufferedReader in = new BufferedReader(
        new InputStreamReader(clientSocket.getInputStream()));
    ) {
      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());
    }
  }
}