UserModel.java

/**
 * Handles getting a user.
 */
public interface UserModel {
   /**
     * @return the currently logged in user, or null if the user is not logged in
     */
    Single<User> getUser();
}

UserModelImpl.java

/**
 * Simplified implementation of {@link UserModel}. The actual implementation of this class caches user in memory, loads it from the database, or from the network.
 */
public class UserModelImpl implements UserModel {
  //UserDb is an interface. Its implementation, UserDbImpl, has android dependencies and actual reads or writes a user to the database.
  //UserDbImpl is part of the `:data` layer.
  UserDb userDb;
  //null by default
  User currentUser;
  
  public UserModelImpl(UserDb userDb) {
        this.userDb = userDb;
  }
  
  @Override
    public Single<User> getUser() {
        return Single.concat(
                Single.just(currentUser),
                userDb.readUser()
        )
                .filter(user -> user != null)
                .first()
                .onErrorReturn(
                        throwable -> {
                            if (throwable instanceof NoSuchElementException) {
                                Timber.d(throwable, "Error");
                                return null;
                            } else {
                                throw new RuntimeException(throwable);
                            }
                        }
                )
                .doOnNext(
                        //cache user in memory so next time the DB doesn't need to be accessed
                        user -> currentUser = user
                )
                .toSingle();
    }
}
  

Based upon what I see here, this looks like a form of a facade (which would be between the UI layer and DB layer). So, not really a data/repository layer. Some people would call this the service layer or a manager of sorts. I hope that helps, it's hard with very little context (and everyones situation is ultimately different).

Apologies, I drastically simplified the code for my UserModelImpl class to use as an example. Maybe too much, so it looks like just a facade. I've updated it to add more complexity.

If I have given you enough context, would you say UserModelImpl belongs in the "business" layer?