Auto injecting logger with guice

Question

With reference to Guice's custom injections article, its TypeListener performs a check for InjectLogger.class annotation - which can be optional. Removing that check will inject to all Logger.class types.

class Log4JTypeListener implements TypeListener {
    public <T> void hear(TypeLiteral<T> typeLiteral, TypeEncounter<T> typeEncounter) {
      for (Field field : typeLiteral.getRawType().getDeclaredFields()) {
        if (field.getType() == Logger.class
            && field.isAnnotationPresent(InjectLogger.class)) {
          typeEncounter.register(new Log4JMembersInjector<T>(field));
        }
      }
    }
  }

I'm tempted to remove "&& field.isAnnotationPresent(InjectLogger.class)" from the listener.

If we're using Guice to inject all instances of our Logger, is there any reason not to do it automatically (without need to annotate)?

Answer 1

I don't know of any programmatic correctness reasons why you wouldn't want to annotate.

I do think you wouldn't want to inject automatically for the sake of code clarity. Dependency Injection can have a bit of a 'magic' feel to it, annotations help clarify the magic and assist developers in understanding what is happening. Essentially, like a type for a variable, a DI annotation is as much for the developer as for the compiler/interpreter.

All that being said, I think if you weren't going to annotate for your logging classes that isn't a huge deal. Most developers don't think a ton about loggers, they just use them (at least that's been my experience). So in this case it would probably be relatively harmless.