new String[] { fessConfig.getIndexFieldThumbnail(), fessConfig.getIndexFieldConfigId() });
            if (doc == null) {
                throw new ThumbnailGenerationException("Document is not found: " + id);
            }
            final String url = DocumentUtil.getValue(doc, fessConfig.getIndexFieldThumbnail(), String.class);
            if (StringUtil.isBlank(url)) {

                    fessConfig.getIndexFieldTitle(), //
                    fessConfig.getIndexFieldDigest(), //
                    fessConfig.getIndexFieldUrl(), //
                    fessConfig.getIndexFieldThumbnail(), //
                    fessConfig.getIndexFieldClickCount(), //
                    fessConfig.getIndexFieldFavoriteCount(), //
                    fessConfig.getIndexFieldConfigId(), //

        try {
            if (fessConfig.isThumbnailCrawlerEnabled()) {
                final ThumbnailManager thumbnailManager = ComponentUtil.getThumbnailManager();
                final String thumbnailField = fessConfig.getIndexFieldThumbnail();
                docList.stream().forEach(doc -> {
                    if (!thumbnailManager.offer(doc)) {
                        if (logger.isDebugEnabled()) {

            putResultDataBody(dataMap, fessConfig.getIndexFieldUrl(), url); // set again
        }
        // thumbnail
        putResultDataBody(dataMap, fessConfig.getIndexFieldThumbnail(), responseData.getUrl());

        // from config
        final String scriptType = crawlingConfig.getScriptType();

        }
        // thumbnail
        final String thumbnailUrl = getThumbnailUrl(responseData, document);
        if (StringUtil.isNotBlank(thumbnailUrl)) {
            putResultDataBody(dataMap, fessConfig.getIndexFieldThumbnail(), thumbnailUrl);
        }

        // from config
        final String scriptType = crawlingConfig.getScriptType();

     * The value is, e.g. thumbnail <br>
     * comment: Field name for thumbnail in the index.
     * @return The value of found property. (NotNull: if not found, exception but basically no way)
     */
    String getIndexFieldThumbnail();

    /**
     * Get the value for the key 'index.field.virtual_host'. <br>
     * The value is, e.g. virtual_host <br>
     * comment: Field name for virtual host in the index.