HttpHandler asyncHandler = (HttpServerExchange exchange) -> {
    client.execute(new HttpGet("https://newton.now.sh/"), new FutureCallback<HttpResponse>() {
        @Override
        public void completed(HttpResponse result) {
            System.out.println("Received.");
            exchange.getResponseSender().send("Received.");
        }

        @Override
        public void failed(Exception ex) {
            System.out.println("Failed.");
            exchange.getResponseSender().send("Failed.");
        }

        @Override
        public void cancelled() {
            System.out.println("Cancelled.");
            exchange.getResponseSender().send("Cancelled.");
        }
    });
};