类中显示声明有参构造方法后，必选显示声明一个无参构造方法，否则报以下错误：
Caused by: org.springframework.beans.BeanInstantiationException: Failed to instantiate [com.xxx.elasticsearch.util.EsUtil]: No default constructor found; nested exception is java.lang.NoSuchMethodException: com.xxx.elasticsearch.util.EsUtil.<init>()