CompositeCallback

public class CompositeCallback<T> implements Callback<T> {
  private List<Callback<T>> mCallbacks = new LinkedList<>();

  public CompositeCallback(Callback<T> callback) {
    add(callback);
  }

  public CompositeCallback<T> add(Callback<T> callback) {
    if (callback != null) {
      mCallbacks.add(callback);
    }
    return this;
  }

  @Override
  public void onResponse(Call<T> call, Response<T> response) {
    for (Callback<T> callback : mCallbacks) {
      callback.onResponse(call, response);
    }
  }

  @Override
  public void onFailure(Call<T> call, Throwable throwable) {
    for (Callback<T> callback : mCallbacks) {
      callback.onFailure(call, throwable);
    }
  }
}