if (creator != null) {
                creator.register(this);
            }
        } catch (final Exception e) {
            if (logger.isDebugEnabled()) {
                logger.debug("CrawlerClientCreator is unavailable.", e);
            }
        }
    }

    /**
     * Adds a client with a regular expression pattern.

    /**
     * Sets a setting value.
     * @param key The key of the setting.
     * @param value The value to set.
     */
    public void set(final String key, final Object value) {
        if (logger.isDebugEnabled()) {
            logger.debug("Set suggest settings. {} key: {} value: {}", settingsIndexName, key, value);
        }
        try {
            client.prepareUpdate()
                    .setIndex(settingsIndexName)

                    return client.execute(request);
                } catch (final MaxLengthExceededException e) {
                    throw e;
                } catch (final Exception e) {
                    if (logger.isDebugEnabled()) {
                        logger.debug("Failed to access to {}", request.getUrl(), e);
                    }

                    if (listener != null) {

                try {
                    final String line = br.readLine();
                    if (line == null) {
                        break;
                    }
                    if (logger.isDebugEnabled()) {
                        logger.debug(line);
                    }
                    list.add(line);
                    if (list.size() > maxLineBuffer) {
                        list.remove(0);

                throw e;
            } catch (final Exception e) {
                if (retryCount > maxRetryCount) {
                    throw e;
                }
                if (logger.isDebugEnabled()) {
                    logger.debug("Failed to invoke actionGet. count:{}", retryCount, e);
                }

        }
        ftpAuthenticationHolder = holder;
    }

    @Override
    public void close() {
        if (ftpAuthenticationHolder == null) {
            return;
        }
        if (logger.isDebugEnabled()) {
            logger.debug("Closing FtpClient...");
        }
        ftpAuthenticationHolder = null;
        for (final FTPClient ftpClient : ftpClientQueue) {
            try {