[스프링 기반 REST API 개발] Bad Request 응답 본문 (Errors, JsonSerializer & @JsonComponent, BindingError&Validator )

spring-boot-starter-validation 의존성 추가

<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-validation</artifactId>
</dependency>

EventDTO

package me.jumen.demoinflearnrestapi.events;

import lombok.AllArgsConstructor;
import lombok.Builder;
import lombok.Data;
import lombok.NoArgsConstructor;

import javax.validation.constraints.Min;
import javax.validation.constraints.NotEmpty;
import javax.validation.constraints.NotNull;
import java.time.LocalDateTime;

@Builder
@NoArgsConstructor
@AllArgsConstructor
@Data
public class EventDto {

    @NotEmpty
    private String name;
    @NotNull
    private String description;
    @NotNull
    private LocalDateTime beginEnrollmentDateTime;
    @NotNull
    private LocalDateTime closeEnrollmentDateTime;
    @NotNull
    private LocalDateTime beginEventDateTime;
    @NotNull
    private LocalDateTime endEventDateTime;
    private String location; // (optional) 이게 없으면 온라인 모임
    @Min(0)
    private int basePrice; // (optional)
    @Min(0)
    private int maxPrice; // (optional)
    @Min(0)
    private int limitOfEnrollment;

}

 

EventController

    @PostMapping
    public ResponseEntity createEvent(@RequestBody @Valid EventDto eventDto, Errors errors) {
        if(errors.hasErrors()) {
            return ResponseEntity.badRequest().build();
          //return ResponseEntity.badRequest().body(errors);
        }
        Event event = modelMapper.map(eventDto, Event.class);

        Event newEvent = this.eventRepository.save(event);

        URI createdUri = linkTo(EventController.class).slash(newEvent.getId()).toUri();
        return ResponseEntity.created(createdUri).body(newEvent);
    }

1. @Valid와 BindingResult(Errors)

@Valid는 @Entity에 바인딩 시 어노테이션을 통해 필드 값들을 검사하면서 검증을 수행한다.

검증을 수행하다 에러가 발생하면 Errors에 에러 값을 넣어준다. 

결론적으로 @Valid의 검증이 선행되기 때문에 BindinResult(Errors)는 항상 @Valid 바로 다음 인자로 선언해야 한다.

 

2. errors를 ResponseEntity body에 담지 못하는 이유? 

Java Bean spec을 준수하는 객체는 BeanSerializer를 통해 JSON으로 serialize 될 수 있다. 

ObjectMapper에는 여러 가지 Serializer가 등록되어 있는데, Errors는 Java Bean spec를 준수하지 않아서 변활 될 수 없다.

controller에서 produces = MediaTypes.HAL_JSON_VALUE로

이를 해결하기 위해 extends JsonSerializer<Errors>

package me.jumen.demoinflearnrestapi.common;

import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.databind.JsonSerializer;
import com.fasterxml.jackson.databind.SerializerProvider;
import org.springframework.boot.jackson.JsonComponent;
import org.springframework.validation.Errors;

import java.io.IOException;
@JsonComponent  // objectMapper에 등록하는 방법
public class ErrorsSerializer extends JsonSerializer<Errors> {
    @Override
    public void serialize(Errors errors, JsonGenerator gen, SerializerProvider serializers) throws IOException {
        gen.writeStartArray();

        errors.getFieldErrors().forEach(e -> {
            try {
                gen.writeStartObject();

                gen.writeStringField("field", e.getField());
                gen.writeStringField("objectName", e.getObjectName());
                gen.writeStringField("code", e.getCode());
                gen.writeStringField("defaultMessage", e.getDefaultMessage());
                Object rejectedValue = e.getRejectedValue();
                if (rejectedValue != null) {
                    gen.writeStringField("rejectedValue", rejectedValue.toString());
                }
                gen.writeEndObject();
            } catch (IOException e1) {
                e1.printStackTrace();
            }

        });

        errors.getGlobalErrors().forEach(e -> {
            try {
                gen.writeStartObject();

                gen.writeStringField("objectName", e.getObjectName());
                gen.writeStringField("code", e.getCode());
                gen.writeStringField("defaultMessage", e.getDefaultMessage());

                gen.writeEndObject();
            } catch (IOException e1) {
                e1.printStackTrace();
            }
        });

        gen.writeEndArray();

    }
}

 

비즈니스 로직을 검사하기 위해 EventValidator 추가

package me.jumen.demoinflearnrestapi.events;

import org.springframework.stereotype.Component;
import org.springframework.validation.Errors;

import java.time.LocalDateTime;

@Component
public class EventValidator {
    public void validate(EventDto eventDto, Errors errors) {
        if (eventDto.getBasePrice() > eventDto.getMaxPrice() && eventDto.getMaxPrice() > 0) {
            errors.rejectValue("basePrice", "wrongValue", "basePrice is wrong.");
            errors.rejectValue("maxPrice", "wrongValue", "maxPrice is wrong.");
        }
        
        LocalDateTime endEventDateTime = eventDto.getEndEventDateTime();
        if (endEventDateTime.isBefore(eventDto.getBeginEventDateTime()) ||
                endEventDateTime.isBefore(eventDto.getCloseEnrollmentDateTime()) ||
                endEventDateTime.isBefore(eventDto.getBeginEnrollmentDateTime())) {
            errors.rejectValue("endEventDateTime", "wrongValue", "endEventDateTime is wrong.");
        }
    }
}

@TestDescription("입력 값이 잘못된 에러가 발생하는 테스트")

@Test
    @TestDescription("입력 값이 잘못된 에러가 발생하는 테스트")
    void createEvent_Bad_Request_Wrong_Input() throws Exception {
        EventDto eventDto = EventDto.builder()
                .name("Spring")
                .description("REST API dev with Spring")
                .beginEnrollmentDateTime(LocalDateTime.of(2020, 12, 26, 12, 12))
                .closeEnrollmentDateTime(LocalDateTime.of(2020, 12, 25, 12, 12))
                .beginEventDateTime(LocalDateTime.of(2020, 12, 28, 12, 12))
                .endEventDateTime(LocalDateTime.of(2020, 12, 27, 12, 12))
                .basePrice(10000)
                .maxPrice(200)
                .limitOfEnrollment(1000)
                .location("D2 Factory")
                .build();

        this.mockMvc.perform(post("/api/events")
                .contentType(MediaType.APPLICATION_JSON)
                .content(this.objectMapper.writeValueAsString(eventDto))
        )
                .andDo(print())
                .andExpect(status().isBadRequest())
                .andExpect(jsonPath("$[0].objectName").exists())
                .andExpect(jsonPath("$[0].defaultMessage").exists())
                .andExpect(jsonPath("$[0].code").exists())
        ;

    }