private final ResourceConfiguration configuration;
    private static final List<Folder> folders = new ArrayList<Folder>();

    public FolderRepositoryImpl(ResourceConfiguration configuration) {
        this.configuration = configuration;
    }

    /**
     * Jeżeli starczy czasu to będzie można ładnie rozłożyć te rzeczy z RepositoryImpl.
     */
    @PostConstruct
    private void init() {
        ObjectMapper objectMapper = new ObjectMapper();
        File inputFile = new File(configuration.getFileName());

        try (FileInputStream fis = new FileInputStream(inputFile)) {
            int iByteCount = fis.read();
            //populate the folders list only if the input file is not empty
            if (iByteCount != -1) {
                JsonNode jsonNode = objectMapper.readValue(inputFile, JsonNode.class);
                Iterator<Map.Entry<String, JsonNode>> iterator = jsonNode.fields();

                while (iterator.hasNext()) {
                    Map.Entry<String, JsonNode> currentIterator = iterator.next();
                    String key = currentIterator.getKey();
                    Folder folder = objectMapper.readValue(currentIterator.getValue().toString(), Folder.class);
                    folder.setPath(key);
                    folders.add(folder);
                }
            }
        } catch (IOException e) {
            System.out.println("Cannot read Folder Data file.");
        }
    }