Project 'Hiya' - Update #4

public class Server {
    
    private static final int SERVER_PORT = 9090;
    
    // All client names, so we can check for duplicates upon registration.
    private static Set<String> names = new HashSet<>();

    // The set of all the print writers for all the clients, used for broadcast.
    private static Set<PrintWriter> writers = new HashSet<>();

    public static void main(String[] args) throws Exception {
        System.out.println("The chat server is running...");
        ExecutorService pool = Executors.newFixedThreadPool(500);
        try (ServerSocket listener = new ServerSocket(SERVER_PORT)) {
            while (true) {
                pool.execute(new Handler(listener.accept()));
            }
        }
    }

    /**
    * The client handler task.
    */
    private static class Handler implements Runnable {
        private boolean nameRequired = true;
        private String name;
        private Socket socket;
        private Scanner in;
        private PrintWriter out;

        public Handler(Socket socket) {
            this.socket = socket;
        }

        public void run() {
            try {
                in = new Scanner(socket.getInputStream());
                out = new PrintWriter(socket.getOutputStream(), true);

                // Keep requesting a name until we get a unique one.
                out.println("SUBMITNAME");
                while(nameRequired && in.hasNextLine()) {
                    name = in.nextLine();
                    synchronized (names) {
                        if(name.equals("QUITHIYA")) {
                            out.println("QUITHIYA");
                        } else if (names.contains(name)) {
                            out.println("DUPLICATEENTRY");
                        } else if (name.equals("")) {
                            out.println("SUBMITNAME");
                        } else {
                            names.add(name);
                            nameRequired = false;
                        }
                    }
                }
                
                // We now have a unique name
                
                out.println("NAMEACCEPTED " + name);
                for (PrintWriter writer : writers) {
                    writer.println("MESSAGE " + name + " has joined");
                }
                writers.add(out);

                // Accept messages from this client and broadcast them.
                while (true) {
                    String input = in.nextLine();
                    if (input.toLowerCase().startsWith("/quit")) {
                        return;
                    }
                    for (PrintWriter writer : writers) {
                        writer.println("MESSAGE " + name + ": " + input);
                    }
                }
            } catch (Exception e) {
                System.out.println(e);
            } finally {
                if (out != null) {
                    writers.remove(out);
                }
                if (name != null) {
                    System.out.println(name + " is leaving");
                    names.remove(name);
                    for (PrintWriter writer : writers) {
                        writer.println("MESSAGE " + name + " has left");
                    }
                }
                try {
                    socket.close();
                } catch (IOException e) {
                }
            }
        }
    }
}

public class Client {

    private static final int SERVER_PORT = 9090;
    private static final String SERVER_HOST = "127.0.0.1";

    Scanner in;
    PrintWriter out;
    JFrame frame = new JFrame("Hiya");
    JTextField textField = new JTextField(50);
    JTextArea messageArea = new JTextArea(16, 50);

    public static void main(String[] args) throws Exception {
        Client client = new Client();
        client.frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        client.frame.setVisible(true);
        client.run();
    }
    
    public Client() {

        textField.setEditable(false);
        messageArea.setEditable(false);        
        frame.getContentPane().add(textField, BorderLayout.SOUTH);
        frame.getContentPane().add(new JScrollPane(messageArea), BorderLayout.WEST);
        frame.pack();

        // Send on enter then clear to prepare for next message
        textField.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                out.println(textField.getText());
                textField.setText("");
            }
        });
    }

    private void run() throws IOException {
        try {
            Socket socket = new Socket(SERVER_HOST, SERVER_PORT);
            in = new Scanner(socket.getInputStream());
            out = new PrintWriter(socket.getOutputStream(), true);

            while (in.hasNextLine()) {
                String line = in.nextLine();
                if (line.startsWith("SUBMITNAME")) {
                    out.println(getName());
                } else if (line.startsWith("NAMEACCEPTED")) {
                    this.frame.setTitle("Hiya - " + line.substring(13));
                    textField.setEditable(true);
                } else if (line.startsWith("MESSAGE")) {
                    if (line.startsWith("MESSAGE-JOIN")) {
                        messageArea.append(line.substring(13) + "\n");
                    } else if(line.startsWith("MESSAGE-LEAVE")) {
                        messageArea.append(line.substring(14) + "\n");
                    } else {
                        messageArea.append(line.substring(8) + "\n");
                    }
                } else if (line.startsWith("DUPLICATEENTRY")) {
                    duplicateAlert();
                    out.println(getName());
                } else if (line.startsWith("QUITHIYA")) {
                    System.exit(0);
                }
            }
        } finally {
            frame.setVisible(false);
            frame.dispose();
        }
    }
    
    // will return null if cancel is pressed
    private String getName() {
        String result = JOptionPane.showInputDialog(frame, "Choose a screen name:", "Screen name selection",
                JOptionPane.PLAIN_MESSAGE);
        if(result == null) {
            return "QUITHIYA";
        } else {
            return result;
        }
    }
    
    // I added this modal to notify the user why the name entered is not acceptable.
    private void duplicateAlert() {
        JOptionPane.showMessageDialog(frame, "Duplicate Entry. Try a different name", "Alert",
                JOptionPane.ERROR_MESSAGE);
    }

}