Repository-like injected object, initialize safely

Question

I would like to create an object that basically functions as a list, and i will inject it in my services, using Guice

public class MyRepository {
  List<MyInterface> list = new ArrayList<>();

  public void add(MyInterface obj){
    list.add(obj);
  } 

  public List<MyInterface> get(){
    return list;
  }
}

Then i am gonna to be using injection from various points to add elements to this list

public class ObjectA implements MyInterface {
  @Inject
  public ObjectA(MyRepository myRepository){
    myRepository.add(this);
  }
}

My question is, i want to ensure that MyRepository is used in services only after all potential subscribers have been added.

Multibinder is not applicable because i will be needed some specific methods

Is there a way to do that? Thanks

Answer 1

If you're using multibinder you're probably wanting to do something like this? You don't want to use static as it would break the @Inject MyRepository repository; logic downstream.

Assuming you have your multibinder configured appropriately then your repository should work like this:

class MyRepository {
   Set<MyInterface> interfaces;

   @Inject
   public MyRepository(Set<MyInterface> interfaces) {
      // Here you can do some things like re-applying the interfaces to
      // a TreeSet (for example) if you needed to control priority.
      this.interfaces = interfaces;
   }

   public Set<Permissions> getPermissions(final User user) {
      // However you want to iterate through the interfaces
      return interfaces.stream()
            .flatMap(i -> i.getPermissions(user)) // maybe?
            .collect(Collectors.toSet());
   }
}

You can have:

• Different methods for iterating the interfaces
• You can filter the interfaces based on other Interfaces. For example if one MyInterface also extends MyOtherInterface

If I'm missing something, please update/comment and we can sort it out.