feat: 현재 로그인한 멤버 조회하는 유틸리티 구현 (#41)

* feat: 멤버 유틸리티 구현

* refactor: 예외 케이스 분리 및 불필요한 메서드 제거

src/main/java/com/gdschongik/gdsc/global/exception/ErrorCode.java

@@ -9,16 +9,19 @@
 public enum ErrorCode {
     INTERNAL_SERVER_ERROR(HttpStatus.INTERNAL_SERVER_ERROR, "서버 에러입니다."),
 
-    // Jwt
+    // Auth
     INVALID_JWT_TOKEN(HttpStatus.UNAUTHORIZED, "유효하지 않은 JWT 토큰입니다."),
     EXPIRED_JWT_TOKEN(HttpStatus.UNAUTHORIZED, "만료된 JWT 토큰입니다."),
+    AUTH_NOT_EXIST(HttpStatus.INTERNAL_SERVER_ERROR, "시큐리티 인증 정보가 존재하지 않습니다."),
+    AUTH_NOT_PARSABLE(HttpStatus.INTERNAL_SERVER_ERROR, "시큐리티 인증 정보 파싱에 실패했습니다."),
 
     // Parameter
     INVALID_QUERY_PARAMETER(HttpStatus.BAD_REQUEST, "잘못된 쿼리 파라미터입니다."),
 
     // Member
     MEMBER_NOT_FOUND(HttpStatus.NOT_FOUND, "존재하지 않는 회원입니다."),
-    MEMBER_DELETED(HttpStatus.CONFLICT, "탈퇴한 회원입니다.");
+    MEMBER_DELETED(HttpStatus.CONFLICT, "탈퇴한 회원입니다."),
+    ;
 
     private final HttpStatus status;
     private final String message;

src/main/java/com/gdschongik/gdsc/global/util/MemberUtil.java

@@ -0,0 +1,41 @@
+package com.gdschongik.gdsc.global.util;
+
+import com.gdschongik.gdsc.domain.member.dao.MemberRepository;
+import com.gdschongik.gdsc.domain.member.domain.Member;
+import com.gdschongik.gdsc.global.exception.CustomException;
+import com.gdschongik.gdsc.global.exception.ErrorCode;
+import lombok.RequiredArgsConstructor;
+import org.springframework.security.core.Authentication;
+import org.springframework.security.core.context.SecurityContextHolder;
+import org.springframework.stereotype.Component;
+
+@Component
+@RequiredArgsConstructor
+public class MemberUtil {
+
+    private final MemberRepository memberRepository;
+
+    public Long getCurrentMemberId() {
+        Authentication authentication = SecurityContextHolder.getContext().getAuthentication();
+
+        validateAuthenticationNotNull(authentication);
+
+        try {
+            return Long.parseLong(authentication.getName());
+        } catch (NumberFormatException e) {
+            throw new CustomException(ErrorCode.AUTH_NOT_PARSABLE);
+        }
+    }
+
+    private void validateAuthenticationNotNull(Authentication authentication) {
+        if (authentication == null) {
+            throw new CustomException(ErrorCode.AUTH_NOT_EXIST);
+        }
+    }
+
+    public Member getCurrentMember() {
+        return memberRepository
+                .findById(getCurrentMemberId())
+                .orElseThrow(() -> new CustomException(ErrorCode.MEMBER_NOT_FOUND));
+    }
+}