unj2 unj2 - 3 years ago 86
Java Question

How do I bind Different Interfaces using Google Guice?

Do I need to create a new module with the Interface bound to a different implementation?

Chef newChef = Guice.createInjector(Stage.DEVELOPMENT, new Module() {
@Override
public void configure(Binder binder) {
binder.bind(FortuneService.class).to(FortuneServiceImpl.class);
}

}).getInstance(Chef.class);

Chef newChef2 = Guice.createInjector(Stage.DEVELOPMENT, new Module() {
@Override
public void configure(Binder binder) {
binder.bind(FortuneService.class).to(FortuneServiceImpl2.class);
}

}).getInstance(Chef.class);


I cannot touch the Chef Class nor the Interfaces. I am just a client binding to Chef's FortuneService to different Interfaces at runtime.

Answer Source

Take looks like the Robot Legs section, described in the Guice FAQ. "How to create a robot with a two Leg objects, the left one injected with a LeftFoot, and the right one with a RightFoot." But only one Leg class that's reused in both contexts.

There's a PrivateModules solution. It uses two separate private modules, a @Left one and an @Right one. Each has a binding for the unannotated Foot.class and Leg.class, and exposes a binding for the annotated Leg.class:

class LegModule extends PrivateModule {
  private final Class<? extends Annotation> annotation;

  LegModule(Class<? extends Annotation> annotation) {
    this.annotation = annotation;
  }

  @Override protected void configure() {
    bind(Leg.class).annotatedWith(annotation).to(Leg.class);
    expose(Leg.class).annotatedWith(annotation);

    bindFoot();
  }

  abstract void bindFoot();
}

...and to glue it all together:

  public static void main(String[] args) {
    Injector injector = Guice.createInjector(
        new LegModule(Left.class) {
          @Override void bindFoot() {
            bind(Foot.class).toInstance(new Foot("leftie"));
          }
        },
        new LegModule(Right.class) {
          @Override void bindFoot() {
            bind(Foot.class).toInstance(new Foot("righty"));
          }
        });
  }
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