前端报跨域错误：
Response to preflight request doesn't pass access control check: No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin 'http://localhost:8080' is therefore not allowed access.
未必是跨域的问题，也有可以是后端的服务器挂了！！！
前端报跨域错误：
Response to preflight request doesn't pass access control check: No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin 'http://localhost:8080' is therefore not allowed access.
未必是跨域的问题，也有可以是后端的服务器挂了！！！