Scala 和 Akka HTTP：请求中的请求和线程问题

Question

我刚开始学习 Scala、Akka Streams 和 Akka HTTP，所以如果问题太基本，请提前道歉。

我想在 HTTP 请求中执行一个 HTTP 请求，就像在下面的一段代码中一样：

  implicit val system = ActorSystem("ActorSystem")
  implicit val materializer = ActorMaterializer
  import system.dispatcher

  val requestHandler: Flow[HttpRequest, HttpResponse, _] = Flow[HttpRequest].map {
    case HttpRequest(HttpMethods.GET, Uri.Path("/api"), _, _, _) =>
      val responseFuture = Http().singleRequest(HttpRequest(uri = "http://www.google.com"))
      responseFuture.onComplete {
        case Success(response) =>
          response.discardEntityBytes()
          println(s"The request was successful")
        case Failure(ex) =>
          println(s"The request failed with: $ex")
      }
      //Await.result(responseFuture, 10 seconds)
      println("Reached HttpResponse")
      HttpResponse(
        StatusCodes.OK
      )
  }

  Http().bindAndHandle(requestHandler, "localhost", 8080)  

但在上述情况下，结果如下所示，这意味着Reached HttpResponse在完成请求之前首先到达：

Reached HttpResponse
The request was successful

我尝试使用Await.result(responseFuture, 10 seconds)（目前已注释掉），但没有任何区别。

我在这里缺少什么？任何帮助将不胜感激！

提前谢谢了！

Answer 1

map是一个接受请求并产生响应的函数：

HttpRequest => HttpResponse

挑战在于响应是一种Future. 因此，您需要一个处理它的函数。该函数接受 HttpRequest 并返回 HttpResponse 的 Future。

HttpRequest => Future[HttpResponse]

瞧，mapAsync正是您所需要的：

val requestHandler: Flow[HttpRequest, HttpResponse, _] = Flow[HttpRequest].mapAsync(2) {
  case HttpRequest(HttpMethods.GET, Uri.Path("/api"), _, _, _) =>
    Http().singleRequest(HttpRequest(uri = "http://www.google.com")).map (resp => {
      resp.discardEntityBytes()
      println(s"The request was successful")
      HttpResponse(StatusCodes.OK)
    })
}