String xpath = configMap.get(Config.HTML_CANONICAL_XPATH);
        if (xpath == null) {
            xpath = fessConfig.getCrawlerDocumentHtmlCanonicalXpath();
        }
        if (StringUtil.isBlank(xpath)) {
            return null;
        }
        final String canonicalUrl = getSingleNodeValue(document, xpath, node -> node);

            }
        };
        transformer.fessConfig = new FessConfig.SimpleImpl() {
            private static final long serialVersionUID = 1L;

            public String getCrawlerDocumentHtmlCanonicalXpath() {
                return "//LINK[@rel='canonical'][1]/@href";
            };
        };

        final ResponseData responseData = new ResponseData();
        responseData.setSessionId("test");