4

我想使用类名创建一个 Akka 演员，如图所示。我尝试了许多 system.actorOf(new Props(theProcessor.getClass), name = "Test") 的变体，但我就是无法让它工作。从类加载器创建 Actor 的任何想法

package com.test

import akka.actor.{Props, Actor, ActorRef, ActorSystem}

object Main {
  def main(args: Array[String]) {
   ActorFromString("Test")
  }
}

object ActorFromString {
  implicit val system = ActorSystem("Test")
  def apply(name: String): ActorRef = {
    val className = "com.test." + name + "Processor"
    val theProcessor: Actor = Class.forName(className).newInstance().asInstanceOf[Actor]
    system.actorOf(new Props(theProcessor.getClass), name = "Test")
  }
}

class TestProcessor extends Actor {
  def receive = {
    case data => println("processing data")
  }
}

Exception in thread "main" akka.actor.ActorInitializationException:
You cannot create an instance of [com.test.TestProcessor] explicitly using the constructor (new).
You have to use one of the factory methods to create a new actor. Either use:
'val actor = context.actorOf(Props[MyActor])'        (to create a supervised child actor from    within an actor), or
'val actor = system.actorOf(Props(new MyActor(..)))' (to create a top level actor from the   ActorSystem)
at akka.actor.ActorInitializationException$.apply(Actor.scala:166)
at akka.actor.Actor$class.$init$(Actor.scala:377)
at com.test.TestProcessor.<init>(ActorFromString.scala:20)
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at  sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:57)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
at java.lang.reflect.Constructor.newInstance(Constructor.java:525)
at java.lang.Class.newInstance0(Class.java:374)
at java.lang.Class.newInstance(Class.java:327)
at com.test.ActorFromString$.apply(ActorFromString.scala:15)
at com.test.Main$.main(ActorFromString.scala:7)
at com.test.Main.main(ActorFromString.scala)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:601)
at com.intellij.rt.execution.application.AppMain.main(AppMain.java:120)

Process finished with exit code 143
4

4 回答 4

7

您可以使用 Java API（仅用于 Props 实例化）：

val myActor = system.actorOf( 
  new Props( Class.forName( "myActorClassName" ).asInstanceOf[Class[Actor]] ) 
)

重要的部分是new关键字。如果你省略它，你将使用 Scala API，它不允许按类实例化。

于 2013-03-28T09:29:04.593 回答
7

听起来您想使用与 ActorSystem 使用的 ClassLoader 相同的 ClassLoader，因此可以使用自定义 Akka 扩展轻松解决此问题（警告，未实际编译，但您会了解它的要点）

import akka.actor.{ Extension, ExtensionId, ExtensionIdProvider, ExtendedActorSystem, DynamicAccess }
// This will be instantiated once per ActorSystem instance
class Reflection(access: DynamicAccess) extends Extension {
  // Loads the Class with the provided Fully Qualified Class Name using the given DynamicAccess
  // Throws exception if it fails to load
  def actorClassFor(fqcn: String) = access.getClassFor[Actor](fqcn).get
}
// This is how we access the Reflection extension, you can view it as an ActorSystemLocal
object Reflect extends ExtensionId[Reflection] with ExtensionIdProvider {
  override def lookup = Reflect
  override def createExtension(system: ExtendedActorSystem) = new Reflection(system.dynamicAccess)
}
// Load the extension if not already loaded, return the instance for this ActorSystem and call the actorClassFor
system.actorOf(Props(Reflect(system).actorClassFor("com.test." + name + "Processor"))
于 2013-03-28T13:24:18.290 回答
4

（如堆栈跟踪所示）您必须使用

  • system.actorOf(Props[TestProcessor]) （没有new关键字，你传递一个类型）
  • 或system.actorOf(Props(new TestProcessor())) （new关键字，您传递一个实例）
于 2013-03-28T06:06:49.247 回答
1

如果您可以从字符串中获取道具，那么您可以从字符串中获取演员。以下是如何从字符串中获取道具：

Props.apply(Class.forName( "myActorClassName" ).asInstanceOf[Class[Actor]])

我提出这个是因为没有其他答案使用Props.apply- Akka 的一个相对较新的增强。很容易传入构造函数参数，例如当前的 actorRef，例如：

def selfActorRef = context.self
val gateKeeperRef = context.actorOf(
  Props.apply(Class.forName(findGateKeeperName).asInstanceOf[Class[Actor]],
  selfActorRef)
)
于 2015-06-30T19:09:19.720 回答