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/
紧急情况的定位
查看mapping列表
curl -v localhost:8081/mappings