Whitelabel Error Page
This application has no explicit mapping for /error, so you are seeing this as a fallback.
Sun Oct 20 17:44:00 CST 2019
There was an unexpected error (type=Bad Request, status=400).
Required String parameter ‘username‘ is not present
4开头 是客户端错误（）Bad Request 错误的请求：数据不对
Required String parameter ‘username‘ is not present
提交的username不存在
400
原文：https://www.cnblogs.com/cai-bai/p/11708309.html
