/**
     * Adds an exclude filter for URLs.
     * URLs matching this regular expression will not be crawled.
     * @param regexp The regular expression for the exclude filter.
     */
    public void addExcludeFilter(final String regexp) {
        if (StringUtil.isNotBlank(regexp)) {
            urlFilter.addExclude(regexp);
        }
    }

    /**
     * Stops the crawling process.