self define indicator
https://docs.spring.io/spring-boot/docs/current/reference/html/production-ready-endpoints.html#_writing_custom_healthindicators
org.springframework.boot.actuate.health.HealthIndicator
http://blog.didispace.com/spring-boot-actuator-1/
原文：https://www.cnblogs.com/yszzu/p/9844890.html