How to @Inject into existing object hierarchy using Guice?

Question

I have an existing object hierarchy where some objects have fields that need to be injected. Also there are some other objects that are constructed using Google Guice and need t

Answer 1

You could inject MembersInjectors to inject nested fields. For example, this will deeply inject an existing Car instance:

public class Car {
  Radio radio;
  List seats;
  Engine engine;

  public Car(...) {...}

  @Inject void inject(RadioStation radioStation,
      MembersInjector seatInjector,
      MembersInjector engineInjector) {
    this.radio.setStation(radioStation);
    for (Seat seat : seats) {
      seatInjector.injectMembers(seat);
    }
    engineInjector.injectMembers(engine);
  }
}

public class Engine {
  SparkPlug sparkPlug;
  Turbo turbo

  public Engine(...) {...}

  @Inject void inject(SparkPlug sparkplug,
      MembersInjector turboInjector) {
    this.sparkPlug = sparkPlug;
    turboInjector.injectMembers(turbo);
  }
}