Example of a Spring ControllerAdvice

ExceptionHandler.kt

@RestControllerAdvice
class ExceptionHandler {

    @ResponseStatus(INTERNAL_SERVER_ERROR) [1]
    @ExceptionHandler(Exception::class)
    fun onException(exception: Exception): ApiError {
        log.error("error=general message=${exception.message}", exception)

        return ApiError("INTERNAL_SERVER_ERROR", exception.message ?: "")
    }

    @ResponseStatus(NOT_ACCEPTABLE) [2]
    @ExceptionHandler(ApiVersionNotAcceptableException::class)
    fun onApiVersionNotAcceptableException(exception: ApiVersionNotAcceptableException): ApiError {
        log.error("error=api version message=${exception.message}", exception)

        return ApiError("VERSION_NOT_ACCEPTABLE", exception.message ?: "")
    }

    @ResponseStatus(BAD_REQUEST) [3]
    @ExceptionHandler(MethodArgumentNotValidException::class)
    fun onMethodArgumentNotValidException(exception: MethodArgumentNotValidException): ApiError {
        log.error("error=validation message=${exception.message}", exception)

        val errors: Map<String, String> = exception
            .bindingResult
            .allErrors
            .associateBy({ (it as FieldError).field }, { it.defaultMessage ?: "" })

        return ApiError("REQUEST_VALIDATION_ERROR", "Some fields are invalid", errors)
    }
}

data class ApiError(
    val code: String,
    val message: String,
    val details: Map<String, String>
)