spring-boot 2.7
https://docs.spring.io/spring-boot/docs/2.7.15/reference/html/
spring framework 5.2.release
https://docs.spring.io/spring-framework/docs/5.2.25.RELEASE/spring-framework-reference/
spring-cloud 2021
https://docs.spring.io/spring-cloud/docs/2021.0.8/reference/html/