Java Akka Scheduling API抛出MissingMethodException

Question

Java 8（好吧，Groovy）在这里使用Akka com.typesafe.akka:akka-actor_2.11:2.5.4。我正在尝试创建一个创建/拥有/管理另一个演员（AppMaster）的演员（StateChecker），并计划每4秒发送一次StateChecker CheckState消息：

class CheckState {}

class StateChecker extends AbstractActor {
  // For this question, it really doesn't matter what this actor does
}

class AppMaster extends AbstractActor {
    ActorRef stateChecker

    @Override
    Receive createReceive() {
      receiveBuilder()
            .match(Init, { message ->
              stateChecker = context.actorOf(Props.create(StateChecker, "yes", 20), "state-checker")

              FiniteDuration startDur = Duration.Zero()

              FiniteDuration freqDur = Duration.create(4000, TimeUnit.MILLISECONDS)
              CheckState checkState = new CheckState()
              ExecutionContextExecutor executor = context.system().dispatcher()

              context.system().scheduler().schedule(startDur, freqDur, stateChecker, checkState,
                executor)
            })
        .build()
    }
}

当我运行它时，我得到以下异常：

groovy.lang.MissingMethodException: No signature of method: akka.actor.LightArrayRevolverScheduler.schedule() is applicable for argument types: (scala.concurrent.duration.FiniteDuration, scala.concurrent.duration.FiniteDuration, akka.actor.LocalActorRef, com.me.myapp.messages.CheckState, akka.dispatch.Dispatcher) values: [0 days, 4000 milliseconds, Actor[akka://myapp/user/myapp-master/o1-keeper#-1837899613], ...]
Possible solutions: schedule(scala.concurrent.duration.FiniteDuration, scala.concurrent.duration.FiniteDuration, java.lang.Runnable, scala.concurrent.ExecutionContext), schedule(scala.concurrent.duration.FiniteDuration, scala.concurrent.duration.FiniteDuration, scala.Function0, scala.concurrent.ExecutionContext), schedule(scala.concurrent.duration.FiniteDuration, scala.concurrent.duration.FiniteDuration, akka.actor.ActorRef, java.lang.Object, scala.concurrent.ExecutionContext, akka.actor.ActorRef)
    at org.codehaus.groovy.runtime.ScriptBytecodeAdapter.unwrap(ScriptBytecodeAdapter.java:58)
    at org.codehaus.groovy.runtime.callsite.PojoMetaClassSite.call(PojoMetaClassSite.java:49)

我添加了日志语句，并在调度期间抛出了异常：

context.system().scheduler().schedule(startDur, freqDur, stateChecker, checkState,
  executor)

知道我需要做些什么来解决这个问题吗？由于这是我在Akka的Java API中遇到的问题，我确实需要通过Java API获得答案。

Answer 1

问题是，您传递给schedule()方法的参数不匹配该方法的重载版本。您可以在schedule()中看到JavaDoc的重载版本的签名。

您尝试使用的版本是以下method：

Cancellable schedule(scala.concurrent.duration.FiniteDuration initialDelay,
                     scala.concurrent.duration.FiniteDuration interval,
                     ActorRef receiver,
                     java.lang.Object message,
                     scala.concurrent.ExecutionContext executor,
                     ActorRef sender)

您错过了最后一个参数，即ActorRef，它被指定为预定消息的发送者。如果StateChecker不关心谁发送CheckState消息，那么最简单的解决方法是传入null作为最后一个参数：

context.system()
       .scheduler()
       .schedule(startDur, freqDur, stateChecker, checkState, executor, null)
                                                                     // ^