[Spring] @InitBinder

(1) @InitBinder 이란?

• WebDataBinder를 초기화 하는 메소드를 지정할 수 있는 설정을 제공합니다.
• 특정 컨트롤러에서 바인딩 또는 검증 설정을 변경하고 싶을 때 사용합니다.
• 모든 요청 전 InitBinder를 선언한 메소드가 실행됩니다.

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(2) 사용법

• Controller

  @RestController
  public class MemberController {
  
  	private final MemberService memberService;
  	private final MemberLoginRequestValidator memberLoginRequestValidator;
      
      @Autowired
      public MemberController(MemberService memberService, MemberLoginRequestValidator memberLoginRequestValidator){
      	this.memberService = memberService;
          this.memberLoginRequestValidator = memberLoginRequestValidator;
      }
  
      //memberLoginRequestDto 객체로 요청이 들어올 경우 memberLoginRequestValidator를 우선 실행
      @InitBinder("memberLoginRequestDto")
      public void loginBinder(WebDataBinder webDataBinder){
          webDataBinder.addValidators(memberLoginRequestValidator);
      }
      
      //로그인
      @PostMapping("/api/member/login")
      public ResponseEntity<Map<String,String>> memberLogin(@Valid @RequestBody MemberLoginRequestDto memberLoginRequestDto, HttpServletResponse httpServletResponse){
  
          return ResponseEntity.ok(memberService.memberLogin(memberLoginRequestDto, httpServletResponse));
      }
  }

• Validator

  @Component
  public class MemberLoginRequestValidator implements Validator {
  
      private final MemberRepository memberRepository;
      private final PasswordEncoder passwordEncoder;
  
      public MemberLoginRequestValidator(MemberRepository memberRepository, PasswordEncoder passwordEncoder){
          this.memberRepository = memberRepository;
          this.passwordEncoder = passwordEncoder;
      }
  
      @Override
      public boolean supports(Class<?> clazz){
          return clazz.isAssignableFrom(MemberLoginRequestDto.class);
      }
  
      @Override
      public void validate(Object object, Errors errors){
          MemberLoginRequestDto memberLoginRequestDto = (MemberLoginRequestDto) object;
  
          if(!memberRepository.existsById(memberLoginRequestDto.getEmail())){
              errors.rejectValue("email", "invalid.email", "존재하지 않는 email입니다.");
          } else {
              MemberEntity memberEntity = memberRepository.getById(memberLoginRequestDto.getEmail());
              if(!passwordEncoder.matches(memberLoginRequestDto.getPassword(), memberEntity.getPassword())) {
                  errors.rejectValue("password","invalid.password", "패스워드가 일치하지 않습니다.");
              }
          }
      }

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