private long expiry = 30 * 24 * 60 * 60 * 1000L;

    public String execute() {
        try {
            final long count = ComponentUtil.getThumbnailManager().purge(getExpiry());
            return "Deleted " + count + " thumbnail files.";
        } catch (final Exception e) {
            logger.error("Failed to purge thumbnails.", e);
            return e.getMessage();
        }
    }