public static void main(String[] args) throws IOException {
    if (args.length != 2) {
      System.out.println("Usage: Crawler <cache dir> <root>");
      return;
    }

    int threadCount = 20;
    long cacheByteCount = 1024L * 1024L * 100L;

    Cache cache = new Cache(new File(args[0]), cacheByteCount);
    OkHttpClient client = new OkHttpClient.Builder()
        .cache(cache)
        .build();