ReactorFibonacci.java

import reactor.core.publisher.Mono;
import reactor.ipc.netty.http.client.HttpClient;
import reactor.ipc.netty.http.client.HttpClientResponse;
import reactor.ipc.netty.http.server.HttpServer;
import reactor.ipc.netty.http.server.HttpServerRoutes;

import java.nio.charset.Charset;
import java.util.function.Consumer;
import java.util.function.Function;

public class ReactorFibonacci {
    private static final String HOST = "localhost";
    private static final int PORT = 8888;

    public static void main(String[] args) {
        Function<Long, Mono<Long>> fibonacci = fibonacci(httpClient());
        Consumer<HttpServerRoutes> routesBuilder = routesBuilder(fibonacci);

        HttpServer httpServer = HttpServer.create(HOST, PORT);
        httpServer.startRouterAndAwait(routesBuilder, null);
    }

    private static Consumer<HttpServerRoutes> routesBuilder(Function<Long, Mono<Long>> fibonacci) {
        return routes -> routes.get("/{n}", (request, response) -> {
            Long n = Long.valueOf(request.param("n"));
            if (n <= 2) {
                return response.sendString(Mono.just("1"));
            } else {
                Mono<Long> n_1 = fibonacci.apply(n - 1);
                Mono<Long> n_2 = fibonacci.apply(n - 2);
                Mono<Long> sum = n_1.and(n_2, Long::sum);
                return response.sendString(sum.map(String::valueOf));
            }
        });
    }

    static HttpClient httpClient() {
        return HttpClient.create(HOST, PORT);
    }

    static Function<Long, Mono<Long>> fibonacci(HttpClient httpClient) {
        return n -> httpClient.get("/" + n)
                .flatMap((Function<HttpClientResponse, Mono<String>>) response -> response
                        .receive()
                        .aggregate()
                        .asString(Charset.forName("UTF-8")))
                .map(Long::valueOf);
    }
}