public class ActionHandler {

    public void doSomething(String message) throws Exception {

        ActionObject actionObj = null;

        if (message.equals("dog")) {
            // ActionObjectDog implements ActionObject
            actionObj = new ActionObjectDog();
        }
        else if (message.equals("cat")) {
            // ActionObjectCat implements ActionObject
            actionObj = new ActionObjectCat();
        }
        else {
            throw new Exception("Action " + message + " not implemented.");
        }

        actionObj.run();
    }
}

@Inject private Provider<ActionObject> actionObjectProvider;

class Module extends AbstractModule {
  @Override protected void configure() {
    MapBinder.newMapBinder(binder(), String.class, ActionObject.class)
        .addBinding("dog").to(ActionObjectDog.class);
    MapBinder.newMapBinder(binder(), String.class, ActionObject.class)
        .addBinding("cat").to(ActionObjectCat.class);
  }
}

class ActionHandler {
  private final Map<String, ActionObject> mappings;
  @Inject ActionHandler(Map<String, ActionObject> mappings) {
    this.mappings = mappings;
  }

  public void doSomething(String message) {
    Preconditions.checkNotNull(mappings.get(message), "No action for '" + message + "'")
        .run();
  }
}