final String docid = DocumentUtil.getValue(docMap, fessConfig.getIndexFieldDocId(), String.class);
        return getImageFilename(docid);
    }

    protected String getImageFilename(final String docid) {
        final StringBuilder buf = new StringBuilder(50);
        for (int i = 0; i < docid.length(); i += splitSize) {
            int hash = docid.substring(i).hashCode() % splitHashSize;

                throw new WebApiException(HttpServletResponse.SC_BAD_REQUEST, "docId is empty.");
            }
            final String docId = docIdObj.toString();
            final String queryId = request.getParameter("queryId");

            final String[] docIds = userInfoHelper.getResultDocIds(URLDecoder.decode(queryId, Constants.UTF_8));
            if (docIds == null) {

            builder.setFetchSource(fields, null);
            queryHelper.processSearchPreference(builder, userBean, docId);
            return true;
        });

    }

    public List<Map<String, Object>> getDocumentListByDocIds(final String[] docIds, final String[] fields,
            final OptionalThing<FessUserBean> userBean, final SearchRequestType searchRequestType) {

# field names
index.field.favorite_count=favorite_count
index.field.click_count=click_count
index.field.config_id=config_id
index.field.expires=expires
index.field.url=url
index.field.doc_id=doc_id
index.field.id=_id
index.field.version=_version
index.field.seq_no=_seq_no
index.field.primary_term=_primary_term
index.field.lang=lang
index.field.has_cache=has_cache
index.field.last_modified=last_modified

    /** The key of the configuration. e.g. url */
    String INDEX_FIELD_URL = "index.field.url";

    /** The key of the configuration. e.g. doc_id */
    String INDEX_FIELD_doc_id = "index.field.doc_id";

    /** The key of the configuration. e.g. _id */
    String INDEX_FIELD_ID = "index.field.id";

    /** The key of the configuration. e.g. _version */