HTTP is a request/response protocol - if a request is sent, then a response is returned, provided that the request reached the server. Whatever HTTP library you're using will tell you one way or the other.
I don't understand what MVC or username/password have to do with this.
HttpServletRequest and HttpServletResponse are
Java classes that are server-side abstractions of HTTP concepts; I sure hope that's not what the interviewer was after.