Question

object Executor extends App {
  implicit val system = ActorSystem()
  implicit val materializer = ActorMaterializer()
  implicit val ec = system.dispatcher
  import akka.stream.io._
  val file = new File("res/AdviceAnimals.tsv")
  import akka.stream.io.Implicits._
  val foreach: Future[Long] = SynchronousFileSource(file)
    .to( Sink.outputStream(()=>System.out))
    .run()

  foreach onComplete { v =>
    println(s"the foreach is ${v.get}")  // the will not be print
  }
}

但如果我将Sink.outputStream(()=>System.out)更改为Sink.ignore，则println(s"the foreach is ${v.get}")会打印出来。

有人可以解释原因吗？

Answer 1

您不是在等待流完成，而是主要方法（Executor的主体）将完成，并且由于主方法已完成退出，JVM将关闭。

您要做的是阻止该线程，并在未来完成之前不退出应用程序。

object Executor extends App {
  // ...your stuff with streams...
  val yourFuture: Future[Long] = ???

  val result = Await.result(yourFuture, 5 seconds)
  println(s"the foreach is ${result}")

  // stop the actor system (or it will keep the app alive)
  system.terminate()
}

Answer 2

巧妙地，我创建了几乎相同的应用程序，用于测试/播放Akka Streams。导入的隐含会导致问题吗？这个应用程序适合我：

object PrintAllInFile extends App {
  val file = new java.io.File("data.txt")

  implicit val system = ActorSystem("test")
  implicit val mat    = ActorMaterializer()
  implicit val ec     = system.dispatcher

  SynchronousFileSource(file)
    .to(Sink.outputStream(() => System.out))
    .run()
    .onComplete(_ => system.shutdown())
}

请注意在'onComplete'中停止ActorSystem。否则应用程序将不会退出。

未来不完整？

2 个答案: