Writing Data to a Client

The following simple program repeatedly answers client requests by sending back the client's address and port. Then it closes the connection.

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

public class HelloServer {

  public final static int defaultPort = 2345;

  public static void main(String[] args) {
  
    int port = defaultPort;
    
    try {
      port = Integer.parseInt(args[0]);
    }
    catch (Exception ex) {
    }
    if (port <= 0 || port >= 65536) port = defaultPort;
    
    try {
      ServerSocket ss = new ServerSocket(port);
      while (true) {
        try {
          Socket s = ss.accept();
          PrintWriter pw = new PrintWriter(s.getOutputStream());
          pw.println("Hello " + s.getInetAddress() + " on port " 
           + s.getPort());
          pw.println("This is " + s.getLocalAddress() + " on port " 
           + s.getLocalPort());
          pw.flush();
          s.close();
        }
        catch (IOException ex) {
        }
      }
    }
    catch (IOException ex) {
      System.err.println(ex);
    }

  }
  
}

Here's some sample output. note how the port from which the connection comes changes each time.

% telnet utopia.poly.edu 2345
Trying 128.238.3.21...
Connected to utopia.poly.edu.
Escape character is '^]'.
Hello fddisunsite.oit.unc.edu/152.2.254.81 on port 51597
This is utopia.poly.edu/128.238.3.21 on port 2345
Connection closed by foreign host.
% !!
telnet utopia.poly.edu 2345
Trying 128.238.3.21...
Connected to utopia.poly.edu.
Escape character is '^]'.
Hello fddisunsite.oit.unc.edu/152.2.254.81 on port 51618
This is utopia.poly.edu/128.238.3.21 on port 2345
Connection closed by foreign host.
%