MahanTCPExample1Telnet.java

package MV3500Cohort2020JulySeptember.homework1;

import java.io.IOException;
import java.io.OutputStream;
import java.io.PrintStream;
import java.net.ServerSocket;
import java.net.Socket;
/**
 * homework assignment
 * @author Bill
 */
public class MahanTCPExample1Telnet
{
    /**
     * Default constructor to silence javadoc warning
     * @see <a href="https://stackoverflow.com/questions/4488716/java-default-constructor" target="_blank">StackOverflow: Java default constructor</a>
     */
    public MahanTCPExample1Telnet ()
    {
        // default initializations 
    }
    /**
     * Program invocation, execution starts here
     * @param args command-line arguments
     */
    public static void main(String[] args) 
    {
        try
        {
            System.out.println("TcpExample1Telnet has started and is waiting for a connection.");
            System.out.println("  help: https://savage.nps.edu/Savage/developers.html#telnet");
            System.out.println("  enter (telnet localhost 2317) or (nc localhost 2317)..." );
			
            // The ServerSocket waits for a connection from a client.
            // It returns a Socket object when the connection occurs.
            ServerSocket serverSocket = new ServerSocket(2317);
            
            // Use Java io classes to write text (as opposed to
            // unknown bytes of some sort) to the client
            
            // The Socket object represents the connection between
            // the server and client, including a full duplex connection
            try (Socket clientConnection = serverSocket.accept()) {
                // Use Java io classes to write text (as opposed to
                // unknown bytes of some sort) to the client
                OutputStream os = clientConnection.getOutputStream();
                PrintStream ps = new PrintStream(os);
                
                ps.println("This client response was written by Bill's server TcpExample1."); // to remote clientnc
                ps.println("When you see something that is not right, not fair, not just, you have to speak up. You have to say something; you have to do something. ");
                System.out.println("This server response was written by Bill's server TcpExample1."); // to server console
                System.out.println("John Lewis");

                // "flush()" in important in that it forces a write
                // across what is in fact a slow connection
                ps.flush();
            }
            System.out.println("TcpExample1 completed successfully.");
        }
        catch(IOException e)
        {
            System.err.println("Problem with TcpExample1Telnet networking:"); // describe what is happening
            System.err.println("Error: " + e);
            // Provide more helpful information to user if exception occurs due to running twice at one time
            
            // brute force exception checking, can be brittle if exception message changes
            // if (e.getMessage().equals("Address already in use: NET_Bind")) 
            if (e instanceof java.net.BindException)
                System.err.println("*** Be sure to stop any other running instances of programs using this port!");
        }
    }
}