BindingResult

@PostMapping("members/new")
public String create(@Valid MemberForm form, BindingResult result) {

    if(result.hasErrors()) {
        return "members/createMemberForm";
    }

    Address address = new Address(form.getCity(), form.getCity(), form.getZipcode());

    Member member = new Member();
    member.setName(form.getName());
    member.setAddress(address);

    memberService.join(member);

    return "redirect:/";
}

@Valid 뒤에 BindingResult를 사용하면 오류가 BindingResult에 담겨서 그 이후 코드가 실행된다.