检查用户是否已登录Spring MVC

Question

我想在登录时获取userName信息.如果用户未登录,则if语句应跳过此操作.我认为暗示是我应该使用但当用户未登录时它当前抛出空指针.

@RequestMapping(value = "/", method = RequestMethod.GET)
public String displayHomePage(Model model, Principal user) {
    if(!user.implies(null)){
        String name = user.getName();
        User currentUser = userService.getUserByName(name);
    }

Answer 1

该Principal参数变量是null,如果用户没有登录,那么请检查是否有这样的无效:

@RequestMapping(value = "/", method = RequestMethod.GET)
public String displayHomePage(Model model, Principal user) {
    if (user != null) {
        String name = user.getName();
        // ...