java - 访问模块内的 Play 2 ActorSystem 引用

Question

根据documentation对于 Play 2.6:

The deprecated static methods play.libs.Akka.system and play.api.libs.concurrent.Akka.system were removed. Use dependency injection to get an instance of ActorSystem and access to the actor system.

该文档提供了一个使用 POJO 注释的示例，但是在模块中使用时该语法似乎不起作用...

我们的类定义如下所示:

public class SomeMagicalModule extends AbstractModule implements AkkaGuiceSupport {...}

1) 尝试在类成员上使用 @Inject 会产生 NULL 引用:

    @Inject
    protected ActorSystem system;

2) 尝试在模块的构造函数上使用 @Inject 会抛出play.api.PlayException:没有有效的构造函数:

    public SomeMagicalModule (@Inject AkkaSystem system) {...}

还有其他途径获得 AkkaSystem，还是我们错过了一些简单的东西？

TIA。

Answer 1

您可以使用@Provides

When you need code to create an object, use an @Provides method. The method must be defined within a module, and it must have an @Provides annotation. The method's return type is the bound type. Whenever the injector needs an instance of that type, it will invoke the method. If the @Provides method has a binding annotation like @PayPal or @Named("Checkout"), Guice binds the annotated type. Dependencies can be passed in as parameters to the method. The injector will exercise the bindings for each of these before invoking the method.

@Provides
CreditCardProcessor providePayPalCreditCardProcessor(@Named("PayPal API key") String apiKey) {
  PayPalCreditCardProcessor processor = new PayPalCreditCardProcessor();
  processor.setApiKey(apiKey);
  return processor;
}

但是，您应该考虑到

Whenever the injector needs an instance of that type, it will invoke the method

因此，如果您有两个依赖于 Provided 组件的组件(在本例中为 CreditCardProcessor)，您最终将得到该组件的 2 个实例，因为Guice 注入(inject)器每次需要注入(inject)该类型的实例时都会调用该方法。

Scopes对此提供解决方案，您必须添加 @Singleton 注释。

@Provides
@Singleton
CreditCardProcessor providePayPalCreditCardProcessor(@Named("PayPal API key") String apiKey) {
  PayPalCreditCardProcessor processor = new PayPalCreditCardProcessor();
  processor.setApiKey(apiKey);
  return processor;
}

就你的情况而言，它将是

public class SomeMagicalModule extends AbstractModule implements AkkaGuiceSupport {

  @Provides
  @Singleton
  @Named("some-actor")
  ActorRef createActor(system: ActorSystem){
    system.actorOf(...)
  }
}

感谢 codejanovic，请参阅 his answer .

无论如何，如果你想要引用 ActorSystem 来创建 Actor，你应该使用 AkkaGuiceSupport (我看到您已经将其添加到您的模块中，但您似乎没有使用它)。