private final Set<HttpUrl> fetchedUrls = Collections.synchronizedSet(new LinkedHashSet<>());
  private final LinkedBlockingQueue<HttpUrl> queue = new LinkedBlockingQueue<>();
  private final ConcurrentHashMap<String, AtomicInteger> hostnames = new ConcurrentHashMap<>();

  public Crawler(OkHttpClient client) {
    this.client = client;
  }

  private void parallelDrainQueue(int threadCount) {

            }

            String hostname = fessConfig.getMailHostname();
            if (StringUtil.isBlank(hostname)) {
                hostname = ComponentUtil.getSystemHelper().getHostname();
            }
            dataMap.put("hostname", hostname);

            logger.debug("\ninfoMap: {}\ndataMap: {}", infoMap, dataMap);