ServerSocketChannel sChannel = null;
    Selector selector = null;
    try {
        sChannel = ServerSocketChannel.open();
        ServerSocket echoServer = sChannel.socket();
        InetSocketAddress addr = new InetSocketAddress(PORT);
        selector = Selector.open();

        echoServer.bind(addr);
        sChannel.configureBlocking(false);
        sChannel.register(selector, SelectionKey.OP_ACCEPT);
        System.out.println("Server running.");
    } catch (IOException e) {//If something goes wrong, the server must be stopped
        e.printStackTrace();
    }

    while(true) {
        try {
            selector.select();
        } catch (IOException e) {
            e.printStackTrace();
        }

        Set<SelectionKey> readyKeys = selector.selectedKeys();
        Iterator<SelectionKey> iterator = readyKeys.iterator();

selector.select()