Basic sever that echoes inputs from a client application...

EchoServer.java

package uk.ac.qub.networking;

import java.io.EOFException;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.net.ServerSocket;
import java.net.Socket;

import javax.swing.JFrame;
import javax.swing.JTextArea;
import javax.swing.JTextField;
import javax.swing.JScrollPane;
import javax.swing.SwingUtilities;

import java.awt.BorderLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

public class EchoServer extends JFrame {

     public static final String PAURICISM = "wee wet";
    // public static final String PAURICISM = "handsome";
    // public static final String PAURICISM = "";
    
    private JTextField enterField; 
    private JTextArea displayArea;
    private ServerSocket server;
    private Socket connection;
    private ObjectOutputStream output;
    private ObjectInputStream input;
    private int counter = 1; // number of connections
    
    public EchoServer() {
        super( "Server" );
        
        enterField = new JTextField();
        enterField.setEditable( false );
        enterField.addActionListener(
                new ActionListener() {
                    public void actionPerformed( ActionEvent event)
                    {
                        sendData( event.getActionCommand() );
                        enterField.setText( "" );
                    }
                }
        );
        
        add ( enterField, BorderLayout.NORTH );
        displayArea = new JTextArea();
        add ( new JScrollPane ( displayArea ), BorderLayout.CENTER);
        setSize( 600, 300 );
        setVisible( true );
        
    }
        
    public void startServer() {
        try {
            server = new ServerSocket (12321, 100);

            while (true) {
                try {
                    waitForConnection();
                    getStreams();
                    processConnection();
                } // end try
                catch (EOFException eofException) {
                    displayMessage("\nYour "+ PAURICISM + "connection was terminted by the server.");
                }
                finally {
                    closeConnection();
                    ++counter;
                }
            } 
        }
        catch (IOException ioException) {
            ioException.printStackTrace();
        }
    }
    
    private void waitForConnection() throws IOException {
        displayMessage("Waiting for a "+ PAURICISM +" connection...");
        connection = server.accept();
        displayMessage("\nA "+ PAURICISM +" "+"connection ("+ counter + ") recieved from: "+
                connection.getInetAddress().getHostName() );
    }
    
    private void getStreams() throws IOException {
        output = new ObjectOutputStream( connection.getOutputStream() );
        output.flush();
        
        input = new ObjectInputStream ( connection.getInputStream() );
        
        displayMessage("\nSome "+ PAURICISM + " I/O streams established.\n");
    }
    
    private void processConnection() throws IOException {
        String message = "Your "+ PAURICISM +" connection was successful.";
        sendData (message);
        
        do {
            try {
                message = ( String ) input.readObject();
                displayMessage("\n"+ message + "\n");
                sendData (message.substring(6));
            } 
            catch (ClassNotFoundException classNotFoundException)
            {
                displayMessage("\nUnknown object type received.");
            } 
        
        } while ( !message.equals( "CLIENT> TERMINATE"));  
    } 
    
    private void closeConnection() {
        displayMessage("\nYour "+ PAURICISM + " connection was terminated.");
        setTextFieldEditable( false );
        
        try {
            output.close();
            input.close();
            connection.close();
        } 
        catch (IOException ioException) 
        {
            ioException.printStackTrace();
        } 
    } 
    
    private void sendData ( String message) {
        try {
            output.writeObject("SERVER> "+ message);
            output.flush();
            displayMessage("SERVER> "+ message);
        }
        catch (IOException ioException)
        {
            displayArea.append("\nError writing object.");
        }
    }
    
    private void displayMessage( final String messageToDisplay ) {
        SwingUtilities.invokeLater(
            new Runnable() {
                public void run() {
                    displayArea.append( messageToDisplay);
                }
            }
        );
    }
    
    private void setTextFieldEditable( final boolean editable) {
        SwingUtilities.invokeLater(
            new Runnable() {
                public void run() {
                    enterField.setEditable( editable );
                }
            }
        );
    }   
    
}