akka设计模式系列-Chain模式

　　链式调用在很多框架和系统中经常存在，算不得上是我自己总结的设计模式，此处只是简单介绍在Akka中的两种实现方式。我在这边博客中简化了链式调用的场景，简化后也更符合Akka的设计哲学。

trait Chained{
  def receive:Receive = Actor.emptyBehavior
}
trait IntReceiveChained1 extends Chained{
  override def receive:Receive = super.receive orElse {
    case i:Int => println(s"IntReceiveChained1 receive Int $i")
  }
}
trait IntReceiveChained extends Chained{
  override def receive:Receive = super.receive orElse {
    case i:Int => println(s"IntReceive receive Int $i")
  }
}
trait StringReceiveChained extends Chained {
  override def receive:Receive = super.receive orElse {
    case i:Int => println(s"StringReceive receive Int $i")
    case s:String => println(s"StringReceive receive String $s")
  }
}
class ChainedActor extends Actor with IntReceiveChained with StringReceiveChained with IntReceiveChained1 {
  override def receive:Receive = super.receive orElse {
    case any =>
      println(s"ChainingActor receive any $any")
  }
}
object ChainingPattern1 {
  def main(args: Array[String]): Unit = {
    val system = ActorSystem("ChainingPattern1",ConfigFactory.load())
    val chainingActor = system.actorOf(Props(new ChainedActor),"ChainedActor")
    chainingActor ! 123
    chainingActor ! "test"
  }
}

输出：

IntReceive receive Int 123
StringReceive receive String test

　　上面这一种实现方式跟akka没有太大关系，是用scala的trait实现的。在类中调用多个Trait中都有的方法时，首先会从最右边的Trait的方法开始执行，然后依次向左执行，形成一个调用条。这个相当于设计模式中的责任链模式的一种具体实现依赖。只不过是用orElse来实现，以保证每种类型的消息都只被处理一次。我们也可以把orElse替换掉，根据条件判断是否继续调用后续函数，这个需要我们根据业务场景来选择，我就不再展开了。

　　

trait Chaining { self => Actor
  private var chainedReceives = List.empty[Receive]
  def registerReceive( newReceive:Receive ): Unit = {
    chainedReceives = newReceive :: chainedReceives
  }
  def receive:Receive = chainedReceives.reduce(_ orElse _)
}
trait IntReceive extends Chaining{
  registerReceive{
    case i:Int => println(s"IntReceive receive Int $i")
  }
}
trait StringReceive extends Chaining {
  registerReceive{
    case s:String => println(s"StringReceive receive String $s")
  }
}
class ChainingActor extends Actor with IntReceive with StringReceive{
}
object ChainingPattern2 {
  def main(args: Array[String]): Unit = {
    val system = ActorSystem("ChainingPattern2",ConfigFactory.load())
    val chainingActor = system.actorOf(Props(new ChainingActor),"chainingActor")
    chainingActor ! 123
    chainingActor ! "test"
  }
}

输出：

IntReceive receive Int 123
StringReceive receive String test

　　这种实现方式是将Receive函数注册到一个列表中，通过reduce把处理函数orElse串起来。与第一种方式一样，对相同的类型也都是只匹配一次。此处只是为了简化设计模式的介绍，读者也都可以根据需求修改对chainedReceives的处理方式，比如所有函数都匹配一遍，或者根据业务条件选择性的匹配。

　　Akka的Chain模式并不常用，但非常有用。有了它，我们就可以自由组合对消息的处理过程了。如果某个receive需要对大量的消息进行处理，我们可以对消息进行分类，创建不同的链式函数去匹配处理，可以做到高内聚低耦合的效果。