Guice:在这种情况下，如何在模块中配置@Provides和@Singleton? [英] Guice: how do you configure an @Provides and @Singleton in a module in this case?

问题描述

我在带有@Provides注释的模块中有一个提供者方法:

I have a provider method in a module annotated with @Provides:

@Provides
public ChatServicePerformanceMonitor getChatServicePerfMon() {
  ...
}

，并且用@Singleton注释了ChatServicePerformanceMonitor.在我使用此实例的代码中，我无法让guice被动地"注入它，因为我正在使用的框架正在构造封闭类(它不使用Guice，所以这是我知道的唯一方法以获得参考):

and I have annotated my ChatServicePerformanceMonitor with @Singleton. In my code, where I use this instance, I can't have guice "passively" inject it, due to a framework I'm using that's constructing the enclosing class (it does not use Guice, so this is the only way I know of to get the reference):

chatServicePerfMon = injector.getInstance(ChatServicePerformanceMonitor.class);

看来Guice不尊重我的ChatServicePerformanceMonitor类上的@Singleton批注.每次调用jector.getInstance(ChatServicePerformanceMonitor.class)都会得到一个实例.

It seems Guice does not respect the @Singleton annotation on my ChatServicePerformanceMonitor class. I get an instance for every call to injector.getInstance(ChatServicePerformanceMonitor.class).

将@Singleton添加到provider方法似乎可以解决此问题:

Adding the @Singleton to the provider method seems to fix this:

@Provides @Singleton
public ChatServicePerformanceMonitor getChatServicePerfMon() {
  ...
}

这是预期的行为吗?看来实例上的@Singleton应该是我所需要的.

Is that the expected behavior? It seems an @Singleton on the instance should be all I would need.

推荐答案

如果要像这样创建ChatServicePerformanceMonitor:

@Provides
public ChatServicePerformanceMonitor getChatServicePerfMon() {
  return new ChatServicePerformanceMonitor();
}

然后，您的课程级别@Singleton注释将无效，因为Guice不会创建对象，而是您会创建. Guice只能在其创建的对象上强制作用域.将@Singleton添加到getChatServicePerfMon()方法没有什么问题.

then your class level @Singleton annotation will have no effect because Guice isn't creating the object, you are. Guice can only enforce scope on objects it creates. There's nothing wrong with adding @Singleton to your getChatServicePerfMon() method.

如果在ChatServicePerformanceMonitor类上具有无参数的构造函数(或@Inject构造函数)，并且删除了@Provides方法，则对注入器的连续调用将返回相同的单例.

If you have a no-argument constructor (or an @Inject constructor) on the ChatServicePerformanceMonitor class and you remove your @Provides method then continual calls to the injector will return the same singleton.

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