private static String extractRoutingValue(String routingField, ElasticSearchConverter.ToStorage toStorage) {
        Object value = toStorage.get(routingField);
        if (value == null) {
            return null;
        }
        return value.toString();
    }
get the value of the field annotated {@link ElasticSearch.Routing}
oap-server/server-storage-plugin/storage-elasticsearch-plugin/src/main/java/org/apache/skywalking/oap/server/storage/plugin/elasticsearch/base/RoutingUtils.java