SpringBoot启动报错【This application has no explicit mapping for /error】

今天做SpringBoot案例的时候，创建SpringBoot程序发现无法访问Controller层的方法，报错：

Whitelabel Error Page

This application has no explicit mapping for /error, so you are seeing this as a fallback.
Wed Mar 14 11:10:52 CST 2018There was an unexpected error (type=Not Found, status=404).No message available

找了半天原因发现，原来SpringBootDemo1Application启动类必须放在包的最外层，才可以扫描加载包下边的其他类。