request.setAttribute("username", username);//一定要保存,OGNL才能获取${username}

public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
request.setCharacterEncoding("utf-8");
String username= request.getParameter("username");
request.setAttribute("username", username);//一定要保存,OGNL才能获取${username}

//也可以保存在session中,但是好像视频说不好

//或者直接在jsp页面中用<%=request.getParameter("username")获取,两种结果一样,但是后者有null
request.getRequestDispatcher("/dologin.jsp").forward(request, response);

}