code: public ClientInterface getRestClientUtil() {
  
  		if(detaultClientInterface == null) {
  			if (restClient != null) {
  				synchronized (this) {
  					if(detaultClientInterface != null)
  						return detaultClientInterface;
  					return detaultClientInterface = this.restClient.getClientUtil(this.indexNameBuilder);
  				}
  			}
  			else
  				return null;
  		}
  		else {
  			return detaultClientInterface;
  		}
  	}
docs: 返回默认的elasticsearch客户端工具api，单例模式，多线程安全
  @return