class FeatureService {

    public List<FeatureDTO> retrieveStateOf(List<String> codes) {
        return codes.stream()
                .filter(code -> this.featureCollection.get(code).isPresent())
                .map(code -> new FeatureDTO(code, this.featureActivator.getState(code)))
                .collect(Collectors.toList());
    }

}