本节主要内容
通过扩展akka.actor.Actor 特质并实现receive方法来定义Actor,代码示例如下
//通过扩展Actor并实现receive方法来定义Actor
class MyActor extends Actor {
//获取LoggingAdapter,用于日志输出
val log = Logging(context.system, this)
//实现receive方法,定义Actor的行为逻辑,返回的是一个偏函数
def receive = {
case "test" => log.info("received test")
case _ => log.info("received unknown message")
}
}
receive方法被定义在Actor当中,方法标签如下
//Actor中的receive方法定义,
type Receive = PartialFunction[Any, Unit]
def receive: Actor.Receive
下面给出其完整使用代码:
object Example_01 extends App{
import akka.actor.Actor
import akka.event.Logging
import akka.actor.ActorSystem
import akka.actor.Props
class MyActor extends Actor {
val log = Logging(context.system, this)
def receive = {
case "test" => log.info("received test")
case _ => log.info("received unknown message")
}
}
//创建ActorSystem对象
val system = ActorSystem("MyActorSystem")
//返回ActorSystem的LoggingAdpater
val systemLog=system.log
//创建MyActor,指定actor名称为myactor
val myactor = system.actorOf(Props[MyActor], name = "myactor")
systemLog.info("准备向myactor发送消息")
//向myactor发送消息
myactor!"test"
myactor! 123
//关闭ActorSystem,停止程序的运行
system.shutdown()
}
代码运行结果:
[INFO] [04/02/2016 09:29:54.223] [main] [ActorSystem(MyActorSystem)] 准备向myactor发送消息
[INFO] [04/02/2016 09:29:54.224] [MyActorSystem-akka.actor.default-dispatcher-3] [akka://MyActorSystem/user/myactor] received test
[INFO] [04/02/2016 09:29:54.224] [MyActorSystem-akka.actor.default-dispatcher-3] [akka://MyActorSystem/user/myactor] received unknown message
输出“[INFO] [04/02/2016 09:29:54.224] [MyActorSystem-akka.actor.default-dispatcher-3] [akka://MyActorSystem/user/myactor] received test”中的[MyActorSystem-akka.actor.default-dispatcher-3]为对应的线程名,[akka://MyActorSystem/user/myactor]为Actor路径信息, received test为
def receive = {
case "test" => log.info("received test")
case _ => log.info("received unknown message")
}
方法处理后的输出。关于[akka://MyActorSystem/user/myactor]路径信息,将在后续内容中进行详细阐述。
也可以通过混入ActorLogging来实现日志功能,具体代码如下:
class MyActor extends Actor with ActorLogging{
def receive = {
case "test" => log.info("received test")
case _ => log.info("received unknown message")
}
}
ActorLogging的定义如下:
trait ActorLogging { this: Actor ⇒
private var _log: LoggingAdapter = _
def log: LoggingAdapter = {
// only used in Actor, i.e. thread safe
if (_log eq null)
_log = akka.event.Logging(context.system, this)
_log
}
}
完整代码如下:
/*
*定义Actor时混入ActorLogging
*/
object Example_02 extends App{
import akka.actor.Actor
import akka.actor.ActorSystem
import akka.actor.Props
class MyActor extends Actor with ActorLogging{
def receive = {
case "test" => log.info("received test")
case _ => log.info("received unknown message")
}
}
//创建ActorSystem对象
val system = ActorSystem("MyActorSystem")
//返回ActorSystem的LoggingAdpater
val systemLog=system.log
//创建MyActor,指定actor名称为myactor
val myactor = system.actorOf(Props[MyActor], name = "myactor")
systemLog.info("准备向myactor发送消息")
//向myactor发送消息
myactor!"test"
myactor! 123
//关闭ActorSystem,停止程序的运行
system.shutdown()
}
代码运行结果:
[INFO] [04/02/2016 09:39:21.088] [main] [ActorSystem(MyActorSystem)] 准备向myactor发送消息
[INFO] [04/02/2016 09:39:21.089] [MyActorSystem-akka.actor.default-dispatcher-3] [akka://MyActorSystem/user/myactor] received test
[INFO] [04/02/2016 09:39:21.089] [MyActorSystem-akka.actor.default-dispatcher-3] [akka://MyActorSystem/user/myactor] received unknown message
代码原理与Example_01类似,这里不再赘述。
在前面两个例子中,通过
val myactor = system.actorOf(Props[MyActor], name = "myactor")
创建Actor,需要注意的是system.actorOf方法返回的是ActorRef对象,ActorRef为Actor的引用,使用ActorRef对象可以进行消息的发送等操作。Props为配置对象,在创建Actor时使用,它是不可变的对象,因此它是线程案例且完全可共享的。Akka中创建Actor时,也允许直接传入MyActor对象的引用,例如
//直接通过new MyActor的方式传入MyActor对象的引用,注意这里是Props(new MyActor)
val myactor = system.actorOf(Props(new MyActor), name = "myactor")
但是Akka不推荐这么做,官方文档给出的解释是这种方式会导致不可序列化的Props对象且可能会导致竞争条件(破坏Actor的封装性)。另外需要特别注意的是,不允许通过下列代码创建Actor
//下列两行代码编译可以通过,但运行时出抛出异常
val myActor=new MyActor
val myactor = system.actorOf(Props(myActor), name = "myactor")
完整运行代码如下:
/*
*创建Actor
*/
object Example_03 extends App{
import akka.actor.Actor
import akka.actor.ActorSystem
import akka.actor.Props
class MyActor extends Actor with ActorLogging{
def receive = {
case "test" => log.info("received test")
case _ => log.info("received unknown message")
}
}
val system = ActorSystem("MyActorSystem")
val systemLog=system.log
//下列两行代码编译可以通过,但运行时出抛出异常
val myActor=new MyActor
val myactor = system.actorOf(Props(myActor), name = "myactor")
systemLog.info("准备向myactor发送消息")
//向myactor发送消息
myactor!"test"
myactor! 123
//关闭ActorSystem,停止程序的运行
system.shutdown()
}
运行结果如下:
Exception in thread "main" akka.actor.ActorInitializationException: You cannot create an instance of [chapter02.Example_03$MyActor] explicitly using the constructor (new). You have to use one of the 'actorOf' factory methods to create a new actor. See the documentation.
at akka.actor.ActorInitializationException$.apply(Actor.scala:167)
at akka.actor.Actor$class.$init$(Actor.scala:423)
at chapter02.Example_03$MyActor.(MyActor.scala:73)
at chapter02.Example_03$delayedInit$body.apply(MyActor.scala:84)
at scala.Function0$class.apply$mcV$sp(Function0.scala:40)
at scala.runtime.AbstractFunction0.apply$mcV$sp(AbstractFunction0.scala:12)
at scala.App$$anonfun$main$1.apply(App.scala:71)
at scala.App$$anonfun$main$1.apply(App.scala:71)
at scala.collection.immutable.List.foreach(List.scala:318)
at scala.collection.generic.TraversableForwarder$class.foreach(TraversableForwarder.scala:32)
at scala.App$class.main(App.scala:71)
at chapter02.Example_03$.main(MyActor.scala:68)
at chapter02.Example_03.main(MyActor.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:606)
at com.intellij.rt.execution.application.AppMain.main(AppMain.java:140)
从“You cannot create an instance of [chapter02.Example_03$MyActor] explicitly using the constructor (new). You have to use one of the ‘actorOf’ factory methods to create a new actor.”可以看到,不能通过显式地调用构造函数创建Actor,只能使用actorOf工厂方法创建Actor。
下面介绍2种在实际中经常使用的Actor创建方法
(1)调用system.actorOf创建Actor
val system = ActorSystem("mySystem")
val myActor = system.actorOf(Props[MyActor], "myactor2")
完整代码在Example_01、Example_02中已经演示过了,这里需要说明的是通过system.actorOf工厂方法创建的Actor为顶级Actor
在Akka框架中,每个Akka应用程序都会有一个守卫Actor,名称为user,所有通过system.actorOf工厂方法创建的Actor都为user的子Actor,也是整个Akka程序的顶级Actor。
(2)调用context.actorOf创建Actor
完整代码如下:
/*
*创建Actor,调用context.actorOf方法
*/
object Example_04 extends App{
import akka.actor.Actor
import akka.actor.ActorSystem
import akka.actor.Props
class FirstActor extends Actor with ActorLogging{
//通过context.actorOf方法创建Actor
val child = context.actorOf(Props[MyActor], name = "myChild")
def receive = {
case x => child ! x;log.info("received "+x)
}
}
class MyActor extends Actor with ActorLogging{
def receive = {
case "test" => log.info("received test")
case _ => log.info("received unknown message")
}
}
val system = ActorSystem("MyActorSystem")
val systemLog=system.log
//创建FirstActor对象
val myactor = system.actorOf(Props[FirstActor], name = "firstActor")
systemLog.info("准备向myactor发送消息")
//向myactor发送消息
myactor!"test"
myactor! 123
Thread.sleep(5000)
//关闭ActorSystem,停止程序的运行
system.shutdown()
}
代码运行结果
[INFO] [04/02/2016 15:05:34.770] [main] [ActorSystem(MyActorSystem)] 准备向myactor发送消息
[INFO] [04/02/2016 15:05:34.771] [MyActorSystem-akka.actor.default-dispatcher-3] [akka://MyActorSystem/user/firstActor/myChild] received test
[INFO] [04/02/2016 15:05:34.771] [MyActorSystem-akka.actor.default-dispatcher-2] [akka://MyActorSystem/user/firstActor] received test
[INFO] [04/02/2016 15:05:34.771] [MyActorSystem-akka.actor.default-dispatcher-2] [akka://MyActorSystem/user/firstActor] received 123
[INFO] [04/02/2016 15:05:34.771] [MyActorSystem-akka.actor.default-dispatcher-3] [akka://MyActorSystem/user/firstActor/myChild] received unknown message
通过代码的运行结果可以看到,FirstActor的Actor路径信息为akka://MyActorSystem/user/firstActor,而通过
class FirstActor extends Actor with ActorLogging{
//通过context.actorOf方法创建Actor
val child = context.actorOf(Props[MyActor], name = "myChild")
def receive = {
case x => child ! x;log.info("received "+x)
}
}
代码使用context.actorOf创建的MyActor,其Actor路径信息为[akka://MyActorSystem/user/firstActor/myChild],这意味着mychild为firstActor的子Actor,层次结构如下图所示
也就是说context.actorOf和system.actorOf的差别是system.actorOf创建的actor为顶级Actor,而context.actorOf方法创建的actor为调用该方法的Actor的子Actor