The Code

Save the following in a file called IdentServer.java:

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

public class IdentServer {
    
    public static void ident(String login) throws IOException {
 
        // Wait for a connection on port 113.
        ServerSocket ss = new ServerSocket(113);
        Socket socket = ss.accept( );
        
        BufferedReader reader = new BufferedReader(
                new InputStreamReader(socket.getInputStream( )));
        BufferedWriter writer = new BufferedWriter(
                new OutputStreamWriter(socket.getOutputStream( )));
        
        // Read the line from the connecting client.
        String line = reader.readLine( );
        if (line != null) {
            System.out.println(line);
            
            // Create our line of reply and send it back.
            line = line + " : USERID : UNIX : " + login;
            System.out.println(line);
            writer.write(line + "\r\n");
            writer.flush( );
        }
        
        // Close the connection and let the program end.
        writer.close( );
        ss.close( );
    }

    public static void main(String[] args) {
        try {
            // Tell the ident server to respond with the login "paul".
            ident("paul");
        }
        catch (IOException e) {
            // If anything goes wrong, print it to the standard output.
            e.printStackTrace( );
        }
    }
    
}