Question

我正在玩Akka Streams并且对通过带参数的函数构建Flow感到好奇。应从前一个流阶段传递参数。

我们假设我们有以下输入和输出：

case class InitElement(v: Int)

trait StreamResult
case class StageA(v: Int) extends StreamResult
case class StageB(v: Int) extends StreamResult

trait StreamFailure extends StreamResult { val msg: String }
case class StageAFailure(msg: String) extends StreamFailure
case class StageBFailure(msg: String) extends StreamFailure

他们的流阶段看起来像：

val stageA = Flow[InitElement].map {
    init => 
      if (init.v > 10) 
        StageA(init.v) 
      else 
        StageAFailure(s"${init.v} less than 10")
  }

  def stageB(input: StreamResult)(externalService: Set[Int]) = Flow[StreamResult].map {
    case failure: StreamFailure => failure
    case StageA(v) => 
      if (externalService.contains(v)) 
        StageB(v)
      else
        StageBFailure(s"$v is absent in external service")
  }

  val graph = Source.single(InitElement(12))
    .via(stageA)
//How can I pass output of previous stage into 'stageB' function?
    .via(stageB(_)(Set(11, 15, 20)))
    .toMat(Sink.head)(Keep.right)

我认为没有办法将stageA的结果传递给构建下一阶段的函数。

我该如何实现？

Answer 1

您对stageB的定义会构建Flow[StreamResult, StreamResult, _]。它不需要将(input: StreamResult)作为参数。请注意，您不要在input定义中的任何位置使用stageB。该元素来自您Flow[StreamResult]上的map。

这应该足够了：

def stageB(externalService: Set[Int]) = … // As you wrote it

val graph = Source.single(InitElement(12))
  .via(stageA)
  .via(stageB(Set(11, 15, 20)))
  .toMat(Sink.head)(Keep.right)

如何从前一阶段传递Akka Stream Flow中的参数？

1 个答案: