akka入门

先来一个官方入门示例

package com.example;

import akka.actor.typed.ActorRef;
import akka.actor.typed.Behavior;
import akka.actor.typed.javadsl.*;

import java.util.Objects;

// #greeter
public class Greeter extends AbstractBehavior<Greeter.Greet> {

  public static final class Greet {
    public final String whom;
    public final ActorRef<Greeted> replyTo;

    public Greet(String whom, ActorRef<Greeted> replyTo) {
      this.whom = whom;
      this.replyTo = replyTo;
    }
  }

  public static final class Greeted {
    public final String whom;
    public final ActorRef<Greet> from;

    public Greeted(String whom, ActorRef<Greet> from) {
      this.whom = whom;
      this.from = from;
    }

// #greeter
    @Override
    public boolean equals(Object o) {
      if (this == o) return true;
      if (o == null || getClass() != o.getClass()) return false;
      Greeted greeted = (Greeted) o;
      return Objects.equals(whom, greeted.whom) &&
              Objects.equals(from, greeted.from);
    }

    @Override
    public int hashCode() {
      return Objects.hash(whom, from);
    }

    @Override
    public String toString() {
      return "Greeted{" +
              "whom='" + whom + '\'' +
              ", from=" + from +
              '}';
    }
// #greeter
  }

  public static Behavior<Greet> create() {
    return Behaviors.setup(Greeter::new);
  }

  private Greeter(ActorContext<Greet> context) {
    super(context);
  }

  @Override
  public Receive<Greet> createReceive() {
    return newReceiveBuilder().onMessage(Greet.class, this::onGreet).build();
  }

  private Behavior<Greet> onGreet(Greet command) {
    getContext().getLog().info("Hello {}!", command.whom);
    //#greeter-send-message
    command.replyTo.tell(new Greeted(command.whom, getContext().getSelf()));
    //#greeter-send-message
    return this;
  }
}
// #greeter

这里要注意，Greet 和Greeted 是作为消息的载体，官方推荐做法是作为内部静态类，原文：

Since messages are the Actor’s public API, it is a good practice to define messages with good names and rich semantic and domain specific meaning, even if they just wrap your data type. This will make it easier to use, understand and debug actor-based systems.

Messages should be immutable, since they are shared between different threads.

It is a good practice to put an actor’s associated messages as static classes in the AbstractBehaavior’s class. This makes it easier to understand what type of messages the actor expects and handles.

It is a good practice obtain an actor’s initial behavior via a static factory method