[Spring boot] ResponseEntity 활용 상태코드 반환, 에러 핸들링

1. ResponseEntity

스프링에서 HTTP의 상태 코드, 헤더, 바디 등을 유연하게 구성할 수 있음.
주로 컨트롤러에서 HTTP 응답을 만들 때 사용.

1) 기본 사용법

import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class MyController {

    @GetMapping("/hello")
    public ResponseEntity<String> hello() {
        return new ResponseEntity<>("Hello, World!", HttpStatus.OK);
    }
}

2. HttpStatus 클래스

org.springframework.http.HttpStatus

주요 HttpStatus 상수

HttpStatus.OK (200 OK)
HttpStatus.CREATED (201 Created)
HttpStatus.ACCEPTED (202 Accepted)
HttpStatus.NO_CONTENT (204 No Content)
HttpStatus.BAD_REQUEST (400 Bad Request)
HttpStatus.UNAUTHORIZED (401 Unauthorized)
HttpStatus.FORBIDDEN (403 Forbidden)
HttpStatus.NOT_FOUND (404 Not Found)
HttpStatus.INTERNAL_SERVER_ERROR (500 Internal Server Error)
HttpStatus.BAD_GATEWAY (502 Bad Gateway)
HttpStatus.SERVICE_UNAVAILABLE (503 Service Unavailable)

3. 다양한 상태코드에 따른 응답 구성

숫자 형태와, HttpStatus enum을 사용하는 방법이 있음. 그러나 HttpStatus enum을 사용하는 것이 더 읽기 쉽고 유지보수하기 쉬운 코드를 작성하는데 도움이 됨.

1) 200 : OK 성공 응답

return ResponseEntity.status(HttpStatus.OK).body("OK");  
return ResponseEntity.ok().body("OK");  
return ResponseEntity.ok("OK");

1) 400 Bad Request : 잘못된 요청 응답

return ResponseEntity.status(400).body("Bad Request");
return ResponseEntity.status(HttpStatus.BAD_REQUEST).body("Bad Request");

2) 401 Unauthorized : 인증 실패

return ResponseEntity.status(401).body("Unauthorized");
return ResponseEntity.status(HttpStatus.UNAUTHORIZED).body("Unauthorized");

3) 403 Forbidden : 권한 부족

return ResponseEntity.status(403).body("Forbidden");
return ResponseEntity.status(HttpStatus.FORBIDDEN).body("Forbidden");

4) 404 Not Found : 찾을 수 없음

return ResponseEntity.status(404).body("Not Found");
return ResponseEntity.status(HttpStatus.NOT_FOUND).body("Not Found");

4) 500 Internal Server Error : 서버 내부 오류

return ResponseEntity.status(500).body("Internal Server Error");
return ResponseEntity.status(HttpStatus.INTERNAL_SERVER_ERROR).body("Internal Server Error");

4. 상태코드 응답 예시

@RestController
@RequestMapping("/api")
public class MyController {

    @GetMapping("/resource")
    public ResponseEntity<?> getResource() {
        try {
            // 리소스를 가져오는 로직
            Object resource = someService.getResource();
            return ResponseEntity.ok(resource);
        } catch (ResourceNotFoundException ex) {
            return ResponseEntity.status(HttpStatus.NOT_FOUND).body("Resource not found");
        } catch (UnauthorizedException ex) {
            return ResponseEntity.status(HttpStatus.UNAUTHORIZED).body("Unauthorized access");
        } catch (BadRequestException ex) {
            return ResponseEntity.badRequest().body("Bad request");
        } catch (Exception ex) {
            return ResponseEntity.status(HttpStatus.INTERNAL_SERVER_ERROR).body("An unexpected error occurred");
        }
    }
}