@CookieValue(name = "memberId", required = false)

두 컨트롤러의 코드는 다음과 같습니다.

LoginController.java

package hello.login.web.login;

import hello.login.domain.login.LoginService;
import hello.login.domain.member.Member;
import lombok.RequiredArgsConstructor;
import lombok.extern.slf4j.Slf4j;
import org.springframework.stereotype.Controller;
import org.springframework.validation.BindingResult;
import org.springframework.validation.annotation.Validated;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.ModelAttribute;
import org.springframework.web.bind.annotation.PostMapping;

import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServletResponse;

@Slf4j
@Controller
@RequiredArgsConstructor
public class LoginController {
    private final LoginService loginService;

    @GetMapping("/login")
    public String loginForm(@ModelAttribute("loginForm") LoginForm form) {
        return "login/loginForm";
    }

    @PostMapping("/login")
    public String login(@Validated @ModelAttribute LoginForm form, BindingResult bindingResult, HttpServletResponse response) {
        if (bindingResult.hasErrors()) {
            return "login/loginForm";
        }
        Member loginMember = loginService.login(form.getLoginId(), form.getPassword());
        if (loginMember == null) {
            bindingResult.reject("loginFail", "아이디 또는 비밀번호가 맞지 않습니다.");
            return "login/loginForm";
        }

        //로그인 성공 처리

        //쿠키에 시간 정보를 주지 않으면 세션 쿠키 (브라우저 종료시 모두 종료)
        Cookie idCookie = new Cookie("memberId", String.valueOf(loginMember.getLoginId()));
        response.addCookie(idCookie);

        return "redirect:/";
    }
}

HomeController.java

package hello.login.web;

import hello.login.domain.member.Member;
import hello.login.domain.member.MemberRepository;
import lombok.RequiredArgsConstructor;
import lombok.extern.slf4j.Slf4j;
import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.web.bind.annotation.CookieValue;
import org.springframework.web.bind.annotation.GetMapping;

@Slf4j
@RequiredArgsConstructor
@Controller
public class HomeController {
    private final MemberRepository memberRepository;

   // @GetMapping("/")
    public String home() {
        return "home";
    }

    @GetMapping("/")
    public String homeLogin(@CookieValue(name = "memberId", required = false) Long memberId, Model model) {
        if (memberId == null) {
            return "home";
        }

        //로그인
        Member loginMember = memberRepository.findById(memberId);
        if (loginMember == null) {
            return "home";
        }

        model.addAttribute("member", loginMember);
        return "loginHome";
    }
}