ChatClient

package chat;

import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.ServerSocket;
import java.net.Socket;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.JTextField;

public class ChatClient {

	//communication variables
	BufferedReader in;
	PrintWriter out;
	String username;
	public static final int PORT = 9001;

	//GUI variables
	JFrame frame;
	JPanel panel;
	JTextField inputField;
	JTextArea messageArea;
	JButton clientButton;
	JButton serverButton;

	ChatServer localServer;
	ServerSocket listener;

	//create GUI
	public ChatClient () {

		//panel and layout manager
		panel = new JPanel(new GridBagLayout());
		GridBagConstraints c = new GridBagConstraints();

		//create and add input field
		c.gridwidth=2;
		c.fill = GridBagConstraints.HORIZONTAL;
		inputField = new JTextField(40);
		inputField.setEditable(false);

		//send text when enter is pressed and clear input field
		inputField.addActionListener(new ActionListener() {

			public void actionPerformed(ActionEvent e) {
				out.println(inputField.getText());
				inputField.setText("");
			}

		});
		panel.add(inputField, c);

		//create and add message area
		c.gridy=1;
		c.weighty=1;
		c.fill = GridBagConstraints.BOTH;
		messageArea = new JTextArea(8,40);
		messageArea.setEditable(false);
		panel.add(new JScrollPane(messageArea), c);

		//create and add "Connect" button
		c.gridy=2;
		c.gridwidth=1;
		c.fill = GridBagConstraints.HORIZONTAL;
		c.weightx=1;
		c.weighty=0;
		clientButton = new JButton("Connect to chatroom");

		//when pressed, connect to server on separate thread
		clientButton.addActionListener(new ActionListener() {

			public void actionPerformed (ActionEvent e) {

				if (in==null && out==null) {

					new Thread(new Runnable() {

						public void run() {

							receiveInput();

						}

					}).start();

				} else if (in!=null&&out!=null) {
					out.println("DISCONNECTING");
				}

			}

		});
		panel.add(clientButton, c);

		//create and add "Start server" button
		serverButton = new JButton("Start chatroom");
		serverButton.addActionListener(new ActionListener() {
			public void actionPerformed (ActionEvent e) {

				new Thread(new Runnable() {

					public void run() {

						//start server
						localServer = new ChatServer();

						new Thread(new Runnable() {

							public void run() {

								if (!localServer.running) {
									try {
										listener.close();
									} catch (IOException e) {
										// TODO Auto-generated catch block
										e.printStackTrace();
									}
								}

							}

						}).start();

						//new listener on port
						try {
							listener = new ServerSocket(PORT);
							//continuously accept new clients
							while (localServer.running) {
								localServer.new Handler(listener.accept()).start();
							}
							localServer = null;
						} catch (IOException serverException) {
							serverException.printStackTrace();
						} finally {
							try {
								listener.close();
							} catch (IOException e) {
								System.out.println("Couldn't close socket");
							}
						}

					}

				}).start();
			}
		});
		panel.add(serverButton, c);

		//create and show frame
		frame = new JFrame("George's Chat Program");
		frame.add(panel);
		frame.pack();
		frame.setLocationRelativeTo(null);
		frame.setDefaultCloseOperation(JFrame.DO_NOTHING_ON_CLOSE);

		//when "X" pressed
		frame.addWindowListener(new WindowAdapter() {
			public void windowClosing (WindowEvent e) {

				if (in==null&&out==null) {
					System.exit(0);
				}

				out.println("DISCONNECTING");
				try {
					Thread.sleep(500);
				} catch (InterruptedException e1) {
					e1.printStackTrace();
				}
				System.exit(0);

			}
		});
		frame.setVisible(true);

	}

	//get desired address from user
	private String getServerAddress () {

		return JOptionPane.showInputDialog(
				frame,
				"Enter IP Address of the Server:",
				"Welcome to George's Chat Program",
				JOptionPane.QUESTION_MESSAGE);

	}

	//get desired screen name from user
	private String getName () {

		return JOptionPane.showInputDialog(
				frame,
				"Choose a screen name:",
				"Screen name selection",
				JOptionPane.PLAIN_MESSAGE);

	}

	//connects to server then begins processing input
	private void receiveInput() {

		//Make connection and initialize streams (try-with-resources YES)
		try (Socket socket = new Socket(getServerAddress(), PORT)) {

			in = new BufferedReader(new InputStreamReader(
					socket.getInputStream()));
			out = new PrintWriter(socket.getOutputStream(), true);
			clientButton.setText("Disconnect from chatroom");
			serverButton.setEnabled(false);

			// Process all messages from server, according to the protocol.
			while (true) {

				String line = in.readLine();

				if (line.startsWith("SUBMITNAME")) {
					while ((username=getName())==null||username.equals("")) {
						JOptionPane.showMessageDialog(frame,"Username cannot be blank.");
					}
					out.println(username);
				} else if (line.startsWith("NAMEACCEPTED")) {
					inputField.setEditable(true);
				} else if (line.startsWith("MESSAGE")) {
					messageArea.append(line.substring(8) + "\n");
				} else if (line.startsWith("BYE")) {
					break;
				}

			}

		} catch (IOException e) {

			JOptionPane.showMessageDialog(frame, "No chat server is running at the specified address.");

			//server has closed or user has disconnected
		} finally {

			in = null;
			out = null;
			clientButton.setText("Connect to chatroom");
			serverButton.setEnabled(true);
			inputField.setEditable(false);
			messageArea.setText("");

		}

	}

	public static void main(String[] args) {

		new ChatClient();

	}

}