public String getSimilarDocHash() {
            return request.getParameter("sdh");
        }

        @Override
        public HighlightInfo getHighlightInfo() {
            return ComponentUtil.getViewHelper().createHighlightInfo();
        }
    }

    /**
     * The request parameters for suggest API.
     */
    protected static class RequestParameter extends SearchRequestParams {

        final FessConfig fessConfig = ComponentUtil.getFessConfig();
        if (doc.get(fessConfig.getResponseFieldUrlLink()) == null) {
            doc.put(fessConfig.getResponseFieldUrlLink(), ComponentUtil.getViewHelper().getUrlLink(doc));
        }
    }

    /**
     * Result of a search operation, including queryId and requestedTime.
     */
    protected static class ChatSearchResult {