1、SpringBoot的入口类一定要放在所有类的上一层，也就是要包含所有子包中的类

springBoot在启动时才会加载所有子包中的所有组件

否则会出现启动成功但是访问不到的情况：

This application has no explicit mapping for /error, so you are seeing this as a fallback.

Wed Dec 14 16:35:25 CST 2016
There was an unexpected error (type=Not Found, status=404).
No message available