@RequestMapping(value = "/login", method = RequestMethod.GET)
	public String toLogin(User user, HttpSession session) {
		User actual = (User) session.getAttribute("user");

		if (Validator.isNull(actual)) {
			return "login/login";
		} else {
			// 如果已登录则直接去后台首页
			return "redirect:/index";
		}
	}