Guice: how do you configure an @Provides and @Singleton in a module in this case?

Question

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

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


        

Answer 1

If you're creating the ChatServicePerformanceMonitor like this:

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

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.

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.