Question

我想通过使用类名创建一个Akka actor，如图所示。我尝试了很多变体的system.actorOf（new Props（theProcessor.getClass），name =“Test”），但我无法让这个工作。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

Answer 1

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。如果省略它，则将使用Scala API，而不允许按类实例化。

Answer 2

听起来你想要使用与ActorSystem使用的ClassLoader相同的ClassLoader，所以这可以通过自定义的Akka扩展轻松解决（警告，实际上没有编译，但你会得到它的要点）

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"))

Answer 3

（如堆栈跟踪中所示）您必须使用

system.actorOf(Props[TestProcessor])（没有new关键字，您传递了一种类型）
或system.actorOf(Props(new TestProcessor()))（new关键字，您传递实例）

Answer 4

如果你可以从String中获取Props，那么你可以从String中获取一个actor。以下是如何从字符串中获取道具：

(defn split-last [re s]
  (let [pattern (re-pattern (str re "(?!.*" re ")"))]
    (split-first pattern s)))

(split-last #"\." "abc.def.ghi")
=> ["abc.def" "ghi"]

(split-last #"<>" "abc<>def<>ghi")
=> ["abc<>def" "ghi"]

我把它放了，因为没有其他答案使用Props.apply(Class.forName( "myActorClassName" ).asInstanceOf[Class[Actor]]) - 对Akka来说是一个相对较新的增强。传递构造函数参数很容易，例如当前的actorRef，例如：

Props.apply

如何根据类名创建一个Akka Actor

4 个答案: