public static boolean isJson(String json) {
        if (StringUtils.isEmpty(json)) {
            return false;
        }
        try {
            new JsonParser().parse(json);
            return true;
        } catch (JsonSyntaxException e) {
            return false;
        }
    }
check whether str is json format
@param json
@return
elasticsearch7/elasticsearch7-sink/src/main/java/com/dtstack/flink/sql/sink/elasticsearch/Es7Util.java