this.imageExtention = imageExtention;
            this.expiry = expiry;
            fessConfig = ComponentUtil.getFessConfig();
            maxPurgeSize = fessConfig.getPageThumbnailPurgeMaxFetchSizeAsInteger();
            searchEngineClient = ComponentUtil.getSearchEngineClient();
        }

        protected void deleteFiles() {
            final Map<String, Path> deleteFileMap = new HashMap<>();

     * @return The value of found property. (NotNull: if not found, exception but basically no way)
     * @throws NumberFormatException When the property is not integer.
     */
    Integer getPageThumbnailPurgeMaxFetchSizeAsInteger();

    /**
     * Get the value for the key 'page.score.booster.max.fetch.size'. <br>
     * The value is, e.g. 1000 <br>