private static final String PDF_DATE = "pdf_date";

    private static final Pattern EMAIL_ADDRESS_PATTERN =
            Pattern.compile("[A-Z0-9._%+-]+@[A-Z0-9.-]+\\.[A-Z]{2,6}", Pattern.CASE_INSENSITIVE);

    private static LoadingCache<String, Long> resourceHashCache =
            CacheBuilder.newBuilder().maximumSize(1000).expireAfterWrite(10, TimeUnit.MINUTES).build(new CacheLoader<String, Long>() {