Spring Exception Handler로 예외처리 재설계 하기

                                    package com.example.liveApiServer.service

import com.example.liveApiServer.dto.save.LikeRequest
import com.example.liveApiServer.dto.save.LikeServerSaveResult
import com.example.liveApiServer.entity.Like
import com.example.liveApiServer.repository.LikeRepository
import org.springframework.stereotype.Service

@Service
class LikeService(
    private val likeRepository: LikeRepository,
) {
    fun save(request: LikeRequest): LikeServerSaveResult{
        return try {
            likeRepository.save(
                Like(
                    id = null, // 이렇게 명시하는게 좋아.
                    boardId = request.boardId,
                    userId = request.userId,
                    likeType = request.likeType,
                )
            )
            LikeServerSaveResult(
                details = null,
                error = null
            )
        }  catch {
            // error 별로 LikeServerSaveResult 관리
            // boardId userId가 없는 경우 어떻게 처리?
            // likeType이 없는 type인 경우도 있을 수 있다.
        }
    }
}

                                    @RestControllerAdvice
class GlobalExceptionHandler {
    // validation error
    @ExceptionHandler(MethodArgumentNotValidException::class)
    fun handleValidationException(ex: MethodArgumentNotValidException): ResponseEntity<ErrorResponse> {
        val message = ex.bindingResult.allErrors.joinToString(", ") { error ->
            val fieldError = error as FieldError
            "${fieldError.field}: ${fieldError.defaultMessage}"
        }
        return ResponseEntity.ok().body(
            ErrorResponse(
                code = FrontServerError.VALIDATION_ERROR,
                message = message
            )
        )
    }
}

                                    💭 서버 어플리케이션 내에 발생할 수 있는 에러는 수 없이 많다.
🤔 에러가 발생하면 그 때마다 Exception Hanlder에 등록해야할까?

                                    package com.example.frontServer.exception

import com.example.frontServer.enum.FrontServerError

open class CustomErrorException(
    val errorCode: FrontServerError,
    override val message: String? = null
) : RuntimeException(message)

                                    package com.example.frontServer.exception

import com.example.frontServer.enum.FrontServerError

class InValidIdException(
    message: String? = "Invalid Id"
): CustomErrorException(FrontServerError.INVALID_ID, message)

                                    // Invalid Id Error
    @ExceptionHandler(InValidIdException::class)
    fun handleCustomErrorException(ex: CustomErrorException): ResponseEntity<ErrorResponse> {
        return ResponseEntity.ok().body(
            ErrorResponse(
                code = ex.errorCode,
                message = ex.message
            )
        )
    }

                                    package com.example.frontServer.service

import com.example.frontServer.dto.*
import com.example.frontServer.dto.board.BoardResult
import com.example.frontServer.dto.board.BoardSaveRequest
import com.example.frontServer.entity.Board
import com.example.frontServer.repository.BoardRepository
import com.example.frontServer.repository.FollowRepository
import jakarta.transaction.Transactional
import org.springframework.stereotype.Service
import java.util.*

@Service
class BoardService(
    val boardRepository: BoardRepository,
    val notificationService: NotificationService,
    val fileService: FileService,
    val followRepository: FollowRepository,
    val timelineService: TimelineService,
    val likeService: LikeService

) {
    @Transactional
    fun findById(id: Long): BoardResult? {
        val boardWithComment = boardRepository.findBoardWithCommentById(id)
        return boardWithComment?.let {
            BoardResult.of(it, it.board.writerId.toString(), 0)
        }
    }
}

                                    @RestController
class BoardController(
    private val boardService: BoardService,
) {
    private val logger = KotlinLogging.logger {}

    @GetMapping("/board")
    fun findById(@RequestBody id: Long): ResponseEntity<BoardResponse> {
        return boardService.findById(id)?.let {
            ResponseEntity.ok().body(
                BoardResponse.of(it)
            )
        } ?: throw InValidIdException()
    }
}

                                    package com.example.frontServer.dto

import com.example.frontServer.enum.FrontServerError

data class ErrorResponse(
    val code: FrontServerError,
    val message: String?
)

                                    package com.example.frontServer.enum

enum class FrontServerError {
    NOT_FOUND_404,           // Wrong URL
    INVALID_ID,              // invalid Id : boardId, userId, ....
    DUPLICATED,              // unique key
    BAD_REQUEST,             // HTTP BAD_REQUEST
    UNEXPECTED_ERROR,        // UnExpected case
    FATAL_SERVER_ERROR,      // fatal server error ex) db connection error
    PARAMETER_ERROR,         // Parameter missing
    VALIDATION_ERROR,        // Sign-up or param validation error
    PARSING_ERROR,           // can't read request body
    CANNOT_ACCESS_RESOURCE,  // can't access resources for network
    CREDENTIALS_ERROR,       // Login failed
    ACCESS_DENIED,           // Failed access to premium service
    BODY_TYPE_ERROR,
    FILE_NOT_EXIST,
}