------------------------下方的username判断是从后端保存在HttpServletRequest request --------------------------
@RequestMapping("/login")
public String loginview(User user, Model model, HttpServletRequest request){
User user1 = userService.getUser(user);
if(user1==null){
model.addAttribute("username",user.getUsername());
model.addAttribute("password",user.getPassword());
model.addAttribute("infoError","用户名或密码错误");
return "index.html";
}else{
request.getSession().setAttribute("user", user1.