Akka并发编程——第四节：Actor模型（三）
本将主要内容：
1. Actor引用、Actor路径
1. Actor引用、Actor路径
下图是Akka官方文档中给出的一张图
该图清晰地说明了ActorPath，ActorRef，Actor及ActorSystem之间的关系，并说明了Actor整体的层次结构。前面我们提到，Akka应用程序会持有一个名称为user的Actor，该Actor被称为guardian supervisor（守卫监督器），无论是ActorSystem创建的Actor还是通过ActorContext创建的Actor都为user的子类，它是最顶级的Actor。
（一）ActorRef
对于ActorRef，我们已经很熟悉了，通过调用ActorSystem.actorOf方法可以创建Actor，返回的便是ActorRef，例如代码
//创建FirstActor对象
val myactor = system.actorOf(Props[FirstActor], name = "firstActor")返回的便是FirstActor的ActorRef对象，ActorRef最重要的作用便是向Actor发送消息，例如
//向myactor发送消息
myactor!"test"
myactor! 123另外，还可以通过context隐式对象获取父Actor和子Actor的ActorRef，示例代码如下：
/*
*Actor API:成员变量self及sender()方法的使用
*/
object Example_07 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
var child:ActorRef = _
override def preStart(): Unit ={
log.info("preStart() in FirstActor")
//通过context上下文创建Actor
child = context.actorOf(Props[MyActor], name = "myActor")
}
def receive = {
//向MyActor发送消息
case x => child ! x;log.info("received "+x)
}
}
class MyActor extends Actor with ActorLogging{
var parentActorRef:ActorRef=_
override def preStart(): Unit ={
//通过context.parent获取其父Actor的ActorRef
parentActorRef=context.parent
}
def receive = {
case "test" => log.info("received test");parentActorRef!"message from ParentActorRef"
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")
//获取ActorPath
val myActorPath=system.child("firstActor")
//通过system.actorSelection方法获取ActorRef
val myActor1=system.actorSelection(myActorPath)
systemLog.info("准备向myactor发送消息")
//向myActor1发送消息
myActor1!"test"
myActor1! 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 20:28:08.941] [MyActorSystem-akka.actor.default-dispatcher-4] [akka://MyActorSystem/user/firstActor] preStart() in FirstActor
[INFO] [04/02/2016 20:28:08.942] [main] [ActorSystem(MyActorSystem)] 准备向myactor发送消息
[INFO] [04/02/2016 20:28:08.943] [MyActorSystem-akka.actor.default-dispatcher-3] [akka://MyActorSystem/user/firstActor] received test
[INFO] [04/02/2016 20:28:08.943] [MyActorSystem-akka.actor.default-dispatcher-3] [akka://MyActorSystem/user/firstActor] received 123
[INFO] [04/02/2016 20:28:08.943] [MyActorSystem-akka.actor.default-dispatcher-4] [akka://MyActorSystem/user/firstActor/myActor] received test
[INFO] [04/02/2016 20:28:08.943] [MyActorSystem-akka.actor.default-dispatcher-4] [akka://MyActorSystem/user/firstActor/myActor] received unknown message
[INFO] [04/02/2016 20:28:08.943] [MyActorSystem-akka.actor.default-dispatcher-3] [akka://MyActorSystem/user/firstActor] received message from ParentActorRef
[INFO] [04/02/2016 20:28:08.943] [MyActorSystem-akka.actor.default-dispatcher-4] [akka://MyActorSystem/user/firstActor/myActor] received unknown message
代码
class MyActor extends Actor with ActorLogging{
var parentActorRef:ActorRef=_
override def preStart(): Unit ={
//通过context.parent获取其父Actor的ActorRef
parentActorRef=context.parent
}
def receive = {
case "test" => log.info("received test");parentActorRef!"message from ParentActorRef"
case _ => log.info("received unknown message");
}
}中，使用
//通过context.parent获取其父Actor的ActorRef
parentActorRef=context.parent获取MyActor 的直接父Actor的ActorRef，在本例中为FirstActor，因为在FirstActor中，我们使用
//通过context上下文创建Actor
child = context.actorOf(Props[MyActor], name = "myActor")创建了MyActor，FirstActor便自动成为MyActor的直接Supervisor。如此便可以通过代码
parentActorRef!"message from ParentActorRef"发送消息。
另外，还可以通过
//创建FirstActor对象
val myactor = system.actorOf(Props[FirstActor], name = "firstActor")
//获取ActorPath
val myActorPath=system.child("firstActor")
//通过system.actorSelection方法获取ActorRef
val myActor1=system.actorSelection(myActorPath)system.actorSelection(myActorPath)方法获取相应的ActorRef。然后再使用获取到的ActorRef向Acto发送消息
//向myActor1发送消息
myActor1!"test"
myActor1! 123现在，让我们来总结一下获取ActorRef的方法：
（1）通过ActorSystem的actorOf方法，不过这种方式是通过创建Actor，然后返回其ActorRef
（2）通过context.actorOf方法，这种方式也是通过创建Actor,然后返回其ActorRef
（3）通过context.parent、context.self、context.children方法获取当前Actor的父Actor、当前Actor及子Actor的ActorRef，这种方式是获取已经创建好的Actor的ActorRef
（4）通过val myActor1=system.actorSelection(myActorPath)方法来获取ActorRef，这种方式也是获取已经创建好的Actor的ActorRef
（二）ActorPath
在前面的例子中，我们通过
val myActorPath=system.child("firstActor")已经使用到了ActorPath。在Akka中，ActorPath采用统一资源定位符的方式进行组织，例如
//本地ActorPath
"akka://my-sys/user/service-a/worker1"
//远程ActorPath
"akka.tcp://[email protected]:5678/user/service-b"本地ActorPath是Akka并发编程中的ActorPath表示方式，而远程ActorPath是Akka分布式编程中常用的ActorPath表示方式，”akka.tcp://[email protected]:5678/user/service-b”中的TCP表示使用的是TCP协议，也可以使用UPD协议，使用UDP协议的远程ActorPath表示方式有如下形式
"akka.udp://my-sys@host.example.com:5678/user/service-b"ActorPath当中，akka.udp表示的是使用的协议，my-sys表示的是ActorSytem名称，host.example.com:5678为远程机器地址及端口，user为guardian supervisor，service-b为当前应用程序的顶级Actor（通过system.actorOf方法创建的）
/*
*ActorPath
*/
object Example_08 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
var child:ActorRef = _
override def preStart(): Unit ={
log.info("preStart() in FirstActor")
//通过context上下文创建Actor
child = context.actorOf(Props[MyActor], name = "myActor")
}
def receive = {
//向MyActor发送消息
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 firstactor = system.actorOf(Props[FirstActor], name = "firstActor")
//获取ActorPath
val firstActorPath=system.child("firstActor")
systemLog.info("firstActorPath--->{}",firstActorPath)
//通过system.actorSelection方法获取ActorRef
val myActor1=system.actorSelection(firstActorPath)
//直接指定其路径
val myActor2=system.actorSelection("/user/firstActor")
//使用相对路径
val myActor3=system.actorSelection("../firstActor")
systemLog.info("准备向myactor发送消息")
//向myActor1发送消息
myActor2!"test"
myActor2! 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 21:04:59.612] [main] [ActorSystem(MyActorSystem)] firstActorPath--->akka://MyActorSystem/user/firstActor
[INFO] [04/02/2016 21:04:59.612] [MyActorSystem-akka.actor.default-dispatcher-2] [akka://MyActorSystem/user/firstActor] preStart() in FirstActor
[INFO] [04/02/2016 21:04:59.615] [main] [ActorSystem(MyActorSystem)] 准备向myactor发送消息
[INFO] [04/02/2016 21:04:59.616] [MyActorSystem-akka.actor.default-dispatcher-4] [akka://MyActorSystem/user/firstActor] received test
[INFO] [04/02/2016 21:04:59.616] [MyActorSystem-akka.actor.default-dispatcher-4] [akka://MyActorSystem/user/firstActor] received 123
[INFO] [04/02/2016 21:04:59.616] [MyActorSystem-akka.actor.default-dispatcher-3] [akka://MyActorSystem/user/firstActor/myActor] received test
[INFO] [04/02/2016 21:04:59.616] [MyActorSystem-akka.actor.default-dispatcher-3] [akka://MyActorSystem/user/firstActor/myActor] received unknown message
本例中的重点代码如下
//获取ActorPath
val firstActorPath=system.child("firstActor")
systemLog.info("myActorPath--->{}",firstActorPath)
//通过system.actorSelection方法获取ActorRef
val myActor1=system.actorSelection(firstActorPath)
//直接指定其路径
val myActor2=system.actorSelection("/user/firstActor")
//使用相对路径
val myActor3=system.actorSelection("../firstActor")通过 val firstActorPath=system.child(“firstActor”)构造一个ActorPath，然后使用
val myActor1=system.actorSelection(firstActorPath)获取路径下的ActorRef，除这种方式外，还可以通过绝对路径 val myActor2=system.actorSelection(“/user/firstActor”)及相对路径 val myActor3=system.actorSelection(“../firstActor”)的方式获取ActorRef
，需要注意的是绝对路径使用的是guardian supevisor，即/user/firstActor的这种方式。
如果要获取myActor，则基方法是类型的，例如
//获取ActorPath
val myActorPath=system.child("firstActor").child("myActor")
systemLog.info("firstActorPath--->{}",myActorPath)
//通过system.actorSelection方法获取ActorRef
val myActor1=system.actorSelection(myActorPath)
//直接指定其路径
val myActor2=system.actorSelection("/user/firstActor/myActor")
//使用相对路径
val myActor3=system.actorSelection("../firstActor/myActor")完整代码如下：
/*
*ActorPath，获取myActor
*/
object Example_09 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
var child:ActorRef = _
override def preStart(): Unit ={
log.info("preStart() in FirstActor")
//通过context上下文创建Actor
child = context.actorOf(Props[MyActor], name = "myActor")
}
def receive = {
//向MyActor发送消息
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 firstactor = system.actorOf(Props[FirstActor], name = "firstActor")
//获取ActorPath
val myActorPath=system.child("firstActor").child("myActor")
systemLog.info("firstActorPath--->{}",myActorPath)
//通过system.actorSelection方法获取ActorRef
val myActor1=system.actorSelection(myActorPath)
//直接指定其路径
val myActor2=system.actorSelection("/user/firstActor/myActor")
//使用相对路径
val myActor3=system.actorSelection("../firstActor/myActor")
systemLog.info("准备向myactor发送消息")
//向myActor1发送消息
myActor1!"test"
myActor1! 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 21:21:14.377] [main] [ActorSystem(MyActorSystem)] firstActorPath--->akka://MyActorSystem/user/firstActor/myActor
[INFO] [04/02/2016 21:21:14.377] [MyActorSystem-akka.actor.default-dispatcher-2] [akka://MyActorSystem/user/firstActor] preStart() in FirstActor
[INFO] [04/02/2016 21:21:14.381] [main] [ActorSystem(MyActorSystem)] 准备向myactor发送消息
[INFO] [04/02/2016 21:21:14.382] [MyActorSystem-akka.actor.default-dispatcher-4] [akka://MyActorSystem/user/firstActor/myActor] received test
[INFO] [04/02/2016 21:21:14.382] [MyActorSystem-akka.actor.default-dispatcher-4] [akka://MyActorSystem/user/firstActor/myActor] received unknown message
关于远程ActorRef的获取，我们将在后续章节中进行讲述。
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