CompletableFuture.kt

fun async() =
    arrayOf(getFutureResponse(100), getFutureResponse(200))
        .let {
            allOf(*it)
                .thenApply { v ->
                    return@thenApply it.map { v1 -> v1.get() }.toMutableList()
                }.thenApply { v ->
                    val delay300res = getFutureResponse(v[0]["totalTimeMillis"].parseLong() + v[1]["totalTimeMillis"].parseLong())
                    delay300res.join()
                    v.add(delay300res.get())
                    return@thenApply v
                }.thenApply { v ->
                    val delay400res = getFutureResponse(v[2]["totalTimeMillis"].parseLong() + 100)
                    val delay500res = getFutureResponse(v[2]["totalTimeMillis"].parseLong() + 200)
                    allOf(delay400res, delay500res)
                        .thenApply {
                            v.add(delay400res.get())
                            v.add(delay500res.get())
                            return@thenApply v
                        }
                }.thenApply { v ->
                    mapOf(
                        "delay100res" to v.get()[0]["totalTimeMillis"],
                        "delay200res" to v.get()[1]["totalTimeMillis"],
                        "delay300res" to v.get()[2]["totalTimeMillis"],
                        "delay400res" to v.get()[3]["totalTimeMillis"],
                        "delay500res" to v.get()[4]["totalTimeMillis"]
                    )
                }
        }

private fun getFutureResponse(ms: Long) = webClient.get()
    .uri("http://$domain:8888/delay/ms/$ms")
    .retrieve()
    .bodyToMono(object : ParameterizedTypeReference<Map<*, *>>() {})
    .toFuture()