spring-boot文档地址：https://docs.spring.io/spring-boot/docs/2.3.3.RELEASE/reference/htmlsingle/
spring 版本下载地址： https://github.com/spring-projects/spring-framework/releases
https://start.spring.io/ 创建项目
注意及建议：
You should only ever add one @SpringBootApplication or @EnableAutoConfiguration annotation. We generally recommend that you add one or the other to your primary @Configuration class only
