一个简单的spring boot 模板 写一个/hello的controller，启动main,访问http://localhost:8080/hello后一直报错：
Whitelabel Error Page
This application has no explicit mapping for /error, so you are seeing this as a fallback.
Tue May 08 13:41:33 CST 2018
There was an unexpected error (type=Not Found, status=404).
No message available
解决办法：
启动main一定要放在groupId下面，我的groupId为com.ly，之前我的放在com.ly.demo下一直出现这个问题，修改到com.ly后成功。