Akka Streams：如何从GraphDSL API获取物化接收器输出？

Question

这是一个非常简单的，使用GraphDSL API的新手问题。我读了几个相关的SO线程和我没有看到答案：

val actorSystem = ActorSystem("QuickStart") 
val executor = actorSystem.dispatcher 
val materializer = ActorMaterializer()(actorSystem) 

val source: Source[Int, NotUsed] = Source(1 to 5) 
val throttledSource = source.throttle(1, 1.second, 1, ThrottleMode.shaping) 
val intDoublerFlow = Flow.fromFunction[Int, Int](i => i * 2) 
val sink = Sink.foreach(println) 

val graphModel = GraphDSL.create() { implicit b => 
    import GraphDSL.Implicits._ 

    throttledSource ~> intDoublerFlow ~> sink 

    // I presume I want to change this shape to something else 
    // but I can't figure out what it is. 
    ClosedShape 
} 
// TODO: This is RunnableGraph[NotUsed], I want RunnableGraph[Future[Done]] that gives the 
// materialized Future[Done] from the sink. I presume I need to use a GraphDSL SourceShape 
// but I can't get that working. 
val graph = RunnableGraph.fromGraph(graphModel) 

// This works and gives me the materialized sink output using the simpler API. 
// But I want to use the GraphDSL so that I can add branches or junctures. 
val graphThatIWantFromDslAPI = throttledSource.toMat(sink)(Keep.right) 

Answer 1

诀窍是通过你想要物化值（在你的情况下，sink）到GraphDSL.create的阶段。您作为第二个参数传递的函数也会发生变化，需要在您的图形中使用Shape输入参数（下例中为s）。

val graphModel: Graph[ClosedShape, Future[Done]] = GraphDSL.create(sink) { implicit b => s => 
    import GraphDSL.Implicits._ 

    throttledSource ~> intDoublerFlow ~> s 

    // ClosedShape is just fine - it is always the shape of a RunnableGraph 
    ClosedShape 
    } 
    val graph: RunnableGraph[Future[Done]] = RunnableGraph.fromGraph(graphModel) 

更多信息可在docs找到。

Answer 2

val graphModel = GraphDSL.create(sink) { implicit b: Builder[Future[Done]] => sink => 
    import akka.stream.scaladsl.GraphDSL.Implicits._ 

    throttledSource ~> intDoublerFlow ~> sink 

    ClosedShape 
} 
val graph: RunnableGraph[Future[Done]] = RunnableGraph.fromGraph(graphModel)  
val graphThatIWantFromDslAPI: RunnableGraph[Future[Done]] = throttledSource.toMat(sink)(Keep.right) 

与GraphDSL API的问题是，隐式生成器负荷过重。您需要将接收器包装在create中，这会将Builder[NotUsed]变成Builder[Future[Done]]，并且现在代表builder => sink => shape而不是builder => shape的功能。