ChatServer

package me.rabrg.chat.net;

import java.io.IOException;
import java.net.InetSocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.SelectionKey;
import java.nio.channels.Selector;
import java.nio.channels.ServerSocketChannel;
import java.nio.channels.SocketChannel;
import java.nio.charset.StandardCharsets;

public final class ChatServer implements Runnable {

    private final InetSocketAddress inetSocketAddress;

    private final ServerSocketChannel serverSocketChannel;

    private final Selector selector;

    private volatile boolean running;

    protected ChatServer(final InetSocketAddress inetSocketAddress) throws IOException {
        this.inetSocketAddress = inetSocketAddress;

        selector = Selector.open();

        serverSocketChannel = ServerSocketChannel.open();
        serverSocketChannel.bind(inetSocketAddress);
        serverSocketChannel.configureBlocking(false);
        serverSocketChannel.register(selector, SelectionKey.OP_ACCEPT);
    }

    public void start() {
        running = true;
        new Thread(this).start();
    }

    @Override
    public void run() {
        try {
            while(running) {
                selector.selectNow();
                for (final SelectionKey selectionKey : selector.selectedKeys()) {
                    if (selectionKey.isValid()) {
                        if (selectionKey.isAcceptable()) {
                            final SocketChannel socketChannel = serverSocketChannel.accept();
                            socketChannel.configureBlocking(false);
                            socketChannel.register(selector, SelectionKey.OP_READ);
                            sendMessage(selectionKey, "Welcome to the server."); // TODO: message constant
                        }
                        if (selectionKey.isReadable()) {
                            final ByteBuffer messageByteBuffer = ByteBuffer.allocate(512);
                            ((SocketChannel) selectionKey.channel()).read(messageByteBuffer);
                            final String message = new String(messageByteBuffer.array(), StandardCharsets.UTF_8);
                            broadcastMessage(message);
                        }
                    }
                }
            }
        } catch (final IOException e) {
            e.printStackTrace();
        }
    }

    public void broadcastMessage(final String message) throws IOException {
        final ByteBuffer messageByteBuffer = ByteBuffer.wrap(message.getBytes());
        for (final SelectionKey selectionKey : selector.keys()) {
            if (selectionKey.isValid()) {
                sendMessage(selectionKey, (ByteBuffer) messageByteBuffer.rewind());
            }
        }
    }

    public void sendMessage(final SelectionKey selectionKey, final String message) throws IOException {
        sendMessage(selectionKey, ByteBuffer.wrap(message.getBytes()));
    }

    public void sendMessage(final SelectionKey selectionKey, final ByteBuffer message) throws IOException {
        System.out.println(message);
        ((SocketChannel) selectionKey.channel()).write(message);
    }

    public void stop() {
        running = false;
    }

    public InetSocketAddress getInetSocketAddress() {
        return inetSocketAddress;
    }
}