/** The key of the configuration. e.g. has_cache */
    String INDEX_FIELD_has_cache = "index.field.has_cache";

    /** The key of the configuration. e.g. last_modified */
    String INDEX_FIELD_last_modified = "index.field.last_modified";

    /** The key of the configuration. e.g. anchor */
    String INDEX_FIELD_ANCHOR = "index.field.anchor";

    /** The key of the configuration. e.g. segment */

    public static final String LABELS_search_result_sort_last_modified_asc = "{labels.search_result_sort_last_modified_asc}";

    /** The key of the message: Last Modified (descending) */
    public static final String LABELS_search_result_sort_last_modified_desc = "{labels.search_result_sort_last_modified_desc}";

    /** The key of the message: Click (ascending) */

  /** The HTTP {@code Expires} header field name. */
  public static final String EXPIRES = "Expires";
  /** The HTTP {@code Last-Modified} header field name. */
  public static final String LAST_MODIFIED = "Last-Modified";
  /** The HTTP {@code Link} header field name. */
  public static final String LINK = "Link";
  /** The HTTP {@code Location} header field name. */
  public static final String LOCATION = "Location";

        if (!outputDirectory.toFile().exists()) {
            return true;
        }

        try (Stream<Path> outputFiles = Files.walk(outputDirectory)) {
            // Not using File#lastModified() to avoid a Linux JDK8 milliseconds precision bug: JDK-8177809.
            long artifactLastModified =
                    Files.getLastModifiedTime(packagedArtifactFile.toPath()).toMillis();

        final long timestamp = propertiesFile.lastModified();
        if (timestamp <= lastModified) {
            return false;
        }

        return true;
    }

    public synchronized void load() {
        final Properties prop = new Properties();
        try (final FileInputStream fis = new FileInputStream(propertiesFile)) {
            lastModified = propertiesFile.lastModified();
            prop.load(fis);

        File metadataFile = new File(localRepository.getBasedir(), metadataPath);
        return metadataFile.isFile() ? new Date(metadataFile.lastModified()) : null;
    }

    private void mergeMetadata(
            RepositoryMetadata metadata,
            List<ArtifactRepository> remoteRepositories,
            ArtifactRepository localRepository)