01_akka入門(java版)

文檔版本:2.4.9 RC1

1.環境

akka需要java8以上版本.

2.入門指導和模板項目

學習akka最好的途徑是下載 Lightbend Activator 並實驗一個akka模板項目.

3.模塊

akka非常的模塊化,是由包含不同特性的jar文件組成.

• akka-actor – Classic Actors, Typed Actors, IO Actor etc.
• akka-agent – Agents, integrated with Scala STM
• akka-camel – Apache Camel integration
• akka-cluster – Cluster membership management, elastic routers.
• akka-osgi – utilities for using Akka in OSGi containers
• akka-osgi-aries – Aries blueprint for provisioning actor systems
• akka-remote – Remote Actors
• akka-slf4j – SLF4J Logger (event bus listener)
• akka-testkit – Toolkit for testing Actor systems

4.使用akka(maven)

通過maven構建akka項目最簡單的方法就是下載 Lightbend Activator的叫做 Akka Main in Java 的教程.

從2.1-M2版本開始akka被髮布到maven中央倉庫,下面是akka-actor依賴實例:

<dependency>
  <groupId>com.typesafe.akka</groupId>
  <artifactId>akka-actor_2.11</artifactId>
  <version>2.4.9-RC1</version>
</dependency>

如果需要使用snapshot版本,還需要添加snapshot庫:

<repositories>
  <repository>
    <id>akka-snapshots</id>
      <snapshots>
        <enabled>true</enabled>
      </snapshots>
    <url>http://repo.akka.io/snapshots/</url>
  </repository>
</repositories>

5.hello world

下載 Lightbend Activator的叫做 Akka Main in Java 的教程.
helloworld項目pom.xml文件:

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">

  <modelVersion>4.0.0</modelVersion>
  <artifactId>akka-sample-main-java</artifactId>
  <groupId>com.typesafe.akka.samples</groupId>
  <name>Akka Main in Java</name>
  <version>1.0</version>

  <properties>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
  </properties>

  <dependencies>
    <dependency>
      <groupId>com.typesafe.akka</groupId>
      <artifactId>akka-actor_2.11</artifactId>
      <version>2.4.4</version>
    </dependency>
  </dependencies>

</project>

Helloworld.java

package sample.hello;

import akka.actor.Props;
import akka.actor.UntypedActor;
import akka.actor.ActorRef;

public class HelloWorld extends UntypedActor {

  @Override
  public void preStart() {
    // create the greeter actor
    final ActorRef greeter = getContext().actorOf(Props.create(Greeter.class), "greeter");
    // tell it to perform the greeting
    greeter.tell(Greeter.Msg.GREET, getSelf());
  }

  @Override
  public void onReceive(Object msg) {
    if (msg == Greeter.Msg.DONE) {
      // when the greeter is done, stop this actor and with it the application
      getContext().stop(getSelf());
    } else
      unhandled(msg);
  }
}

Greeter.java

package sample.hello;

import akka.actor.UntypedActor;

public class Greeter extends UntypedActor {

  public static enum Msg {
    GREET, DONE;
  }

  @Override
  public void onReceive(Object msg) {
    if (msg == Msg.GREET) {
      System.out.println("Hello World!");
      getSender().tell(Msg.DONE, getSelf());
    } else
      unhandled(msg);
  }

}

HelloWorld actor是應用的main class,當它終結時程序被關閉.主業務邏輯發生在preStart方法,Greeter actor被創建,並且等待HelloWorld發起一個問候(GREET).當HelloWorld一個問候(GREET)通過發送後端消息發送給Greeter,Greeter會通過onReceive方法接收,打印”Hello World”後,再返回一個消息(DONE)告訴HelloWorld問候一句收到,HelloWorld通過onReceive接收到這消息(DONE)後關閉HelloWorld actor.

Main.java

package sample.hello;

public class Main {

  public static void main(String[] args) {
    akka.Main.main(new String[] { HelloWorld.class.getName() });
  }
}

Main.java實際上只是一個小包裝的通用類akka.Main,它只需要一個參數:應用程序主actor的類名這主方法將創建運行actor所需的基礎設施,啓動給定主要actor和安排整個應用程序關閉。因此你可以使用下面的命令運行應用程序:
java -classpath akka.Main sample.hello.HelloWorld

如果你需要比akka.Main更多的控制啓動代碼,你可以參考Main2.java編寫自己的主類.
Main2.java

package sample.hello;

import akka.actor.ActorRef;
import akka.actor.ActorSystem;
import akka.actor.Props;
import akka.actor.Terminated;
import akka.actor.UntypedActor;
import akka.event.Logging;
import akka.event.LoggingAdapter;

public class Main2 {

  public static void main(String[] args) {
    ActorSystem system = ActorSystem.create("Hello");
    ActorRef a = system.actorOf(Props.create(HelloWorld.class), "helloWorld");
    system.actorOf(Props.create(Terminator.class, a), "terminator");
  }

  public static class Terminator extends UntypedActor {

    private final LoggingAdapter log = Logging.getLogger(getContext().system(), this);
    private final ActorRef ref;

    public Terminator(ActorRef ref) {
      this.ref = ref;
      getContext().watch(ref);
    }

    @Override
    public void onReceive(Object msg) {
      if (msg instanceof Terminated) {
        log.info("{} has terminated, shutting down system", ref.path());
        getContext().system().terminate();
      } else {
        unhandled(msg);
      }
    }

  }
}