如何在 Spring Boot REST API 中将 null 值包含到 JSON 响应

Question

我正在开发 RESTful API。我想通过调用API来获取用户详细信息。但我的预期响应不包含空值。

预期回应

{
    "id": 1,
    "username": "admin",
    "fullName": "Geeth Gamage",
    "userRole": "ADMIN",
    "empNo": null
} 

实际反应

  {
        "id": 1,
        "username": "admin",
        "fullName": "Geeth Gamage",
        "userRole": "ADMIN"
    } 

我的 Spring boot Rest API 代码如下。为什么我的响应不包含空参数？

@GetMapping(value = "/{userCode}", produces = MediaType.APPLICATION_JSON_VALUE)
public ResponseEntity<Object> findUser(@PathVariable String userCode)
{
    return ResponseEntity.status(HttpStatus.OK).body(userService.getUserByUserName(userCode));
}


@Override
@Transactional
public Object getUserByUserName(String username)
{
    try {
        User user = Optional.ofNullable(userRepository.findByUsername(username))
                   .orElseThrow(() -> new ObjectNotFoundException("User Not Found"));
            
            return new ModelMapper().map(user, UserDTO.class);

    } catch (ObjectNotFoundException ex) {
        log.error("Exception  :  ", ex);
        throw ex;
    } catch (Exception ex) {
        log.error("Exception  :  ", ex);
        throw ex;
    }
}

User

实体类和

UserDTO

对象类如下

用户.class

@Data
@Entity
@Table(name = "user")
public class User{
    @Id
    @GeneratedValue(strategy = IDENTITY)
    @Column(name = "ID", unique = true, nullable = false)
    private Long id;
    @Column(name = "USERNAME", nullable = false, length = 64)
    private String username;
    @Column(name = "USER_ROLE", nullable = false)
    private String userRole;
    @Column(name = "EMP_NO")
    private String empNo;
}

UserDTO.class

@Data
public class  UserDTO {
    private Long id;
    private String username;
    private String fullName;
    private String userRole;
    private String empNo;
}

Answer 1

假设您使用的是 Jackson，您可以使用 setSerializationInclusion(JsonInclude.Include) 上的

ObjectMapper

配置其

global

行为。

对于您的用例，您可以将其配置为 NON_EMPTY 或 ALWAYS。有关更多详细信息，请查看https://fasterxml.github.io/jackson-annotations/javadoc/2.6/com/fasterxml/jackson/annotation/JsonInclude.Include.html。

您还可以使用相应的注释在类或属性级别执行此操作

@JsonInclude

。

Answer 2

我所做的是 Jao Dias 提到的：在项目级别设置 SerializationInclusion。因此，为了让我的 Rest API 响应将字段显示为空（在杰克逊序列化期间被省略），前两个不起作用，即 yaml 文件和注册 bean 不起作用。

 spring:
        profiles: local        
         jackson.default-property-inclusion: always

甚至添加了一个配置bean

@Bean
    public Jackson2ObjectMapperBuilderCustomizer jsonCustomizer() {

        return builder -> builder.serializationInclusion(JsonInclude.Include.ALWAYS);
    }

我想，由于对我来说问题是 RequestMappingHandler 而不是 Jackson 序列化，所以我必须解决并在 Spring 容器设置期间注册它。

    @Component
public class JacksonFix {
    private RequestMappingHandlerAdapter requestMappingHandlerAdapter;
    

    @PostConstruct
    public void init() {
        List<HttpMessageConverter<?>> messageConverters = requestMappingHandlerAdapter.getMessageConverters();
        for (HttpMessageConverter<?> messageConverter : messageConverters) {
            if (messageConverter instanceof MappingJackson2HttpMessageConverter) {
                MappingJackson2HttpMessageConverter m = (MappingJackson2HttpMessageConverter) messageConverter;
        m.getObjectMapper().setSerializationInclusion(JsonInclude.Include.ALWAYS);
                
            }
        }
    }

    private JacksonFix() {
        new AssertionError("instantiation of this class not allowed");
    }

    
    @Autowired
    public void setAnnotationMethodHandlerAdapter(RequestMappingHandlerAdapter requestMappingHandlerAdapter) {
        this.requestMappingHandlerAdapter  = requestMappingHandlerAdapter;
    }