Spring对象映射器covertValue方法不转换某些字段

Question

我有一个 Spring Boot 2 应用程序，它使用 ObjectMapper.convertValue 方法在实体和 DTO 之间进行转换。

我一直在试图理解为什么该方法不转换某些字段，具体来说，看看以下场景：

产品实体：

@Entity
@Table(name = "product")
@Getter
@Setter
@NoArgsConstructor(access = AccessLevel.PUBLIC)
@AllArgsConstructor
public class Product extends AbstractPersistable<Long> {

    @Column
    private String name;

    @Column
    private String description;

    @Column
    private BigDecimal price;

    @Column
    private int weight;

    @Column
    private int stock = 0;

    @Column(name = "image_url", length = 254, unique = true)
    private String imageUrl;

    @NotEmpty
    @Column(name = "banner_image_url", length = 254, unique = true)
    private String bannerImageUrl;

    @ManyToOne(optional = false, fetch = FetchType.EAGER, cascade = CascadeType.ALL)
    @JoinColumn(name = "product_category_id")
    @JsonBackReference
    private Category category;

    @OneToMany(mappedBy = "product", fetch = FetchType.EAGER, cascade = CascadeType.ALL)
    @OrderBy
    @JsonManagedReference
    private SortedSet<ProductThumbnail> thumbnails;

    public Product(Long id) {
        this.setId(id);
    }

    public Product(String name, String description, BigDecimal price, int weight) {
        this.name = name;
        this.description = description;
        this.price = price;
        this.weight = weight;
    }
}

产品 DTO：

@Getter
@Setter
@NoArgsConstructor
public class ProductDTO {

    private Long id;

    private String name;

    private String description;

    private BigDecimal price;

    private int weight;

    private String imageUrl;

    private String bannerImageUrl;

    private CategoryDTO category;

    private SortedSet<ProductThumbnailDTO> thumbnails;

    public ProductDTO(@JsonProperty("id") Long id) {
        this.id = id;
    }

    @JsonCreator
    public ProductDTO(@JsonProperty("id") Long id,
                      @JsonProperty("name") String name,
                      @JsonProperty("description") String description,
                      @JsonProperty("price") BigDecimal price,
                      @JsonProperty("weight") int weight,
                      @JsonProperty("imageUrl") String imageUrl,
                      @JsonProperty("category") CategoryDTO category,
                      @JsonProperty("variants") Set<ProductVariantDTO> variants) {
        this.id = id;
        this.name = name;
        this.description = description;
        this.price = price;
        this.weight = weight;
        this.imageUrl = imageUrl;
        this.category = category;
        this.variants = variants;
    }
}

执行以下代码时，每个字段都会自动转换：

ProductDTO productDTO = objectMapper.convertValue(product, ProductDTO.class);

但category 除外。所以设置了product变量中的category，而转换后得到的productDTO.category字段为null。

类别实体：

@Entity
@Table(name = "product_category")
@Getter
@Setter
@NoArgsConstructor(access = AccessLevel.PUBLIC)
@AllArgsConstructor
@Immutable
public class Category extends AbstractPersistable<Long> {

    @Column
    private String name;

    @Column
    private String description;

    @OneToMany(mappedBy = "category", cascade = CascadeType.ALL, fetch = FetchType.LAZY)
    @JsonManagedReference
    private Set<Product> products = new HashSet<>();
}

类别 DTO：

@Data
@NoArgsConstructor
public class CategoryDTO {

    private String name;

    private String description;

    @JsonIgnore
    private Set<Product> products = new HashSet<>();

    @JsonCreator
    public CategoryDTO(@JsonProperty("name") String name, @JsonProperty("description") String description) {
        this.name = name;
        this.description = description;
    }
}

所以问题是，为什么 ObjectMapper 也不能自动转换类别字段？是否有任何条件阻止它发生？因为根本没有抛出任何错误。

下面是objectmapper bean：

@Bean
public ObjectMapper objectMapper() {
    ObjectMapper objectMapper = new ObjectMapper();
    objectMapper.enable(MapperFeature.ACCEPT_CASE_INSENSITIVE_ENUMS);
    objectMapper.disable(SerializationFeature.FAIL_ON_EMPTY_BEANS);
    objectMapper.setSerializationInclusion(JsonInclude.Include.NON_NULL);
    objectMapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
    objectMapper.findAndRegisterModules();
    objectMapper.registerModules(module(), new Jdk8Module());
    return objectMapper;
}

jackson dep 版本 2.10.1

谢谢

Answer 1

所以代码中的罪魁祸首是@JsonBackReference。由于@JsonBackReference注解分配给

    @JsonBackReference
    private Category category;

此类别在序列化时会自动删除。来自this reference:

@JsonManagedReference 是引用的前向部分——正常序列化的部分。 @JsonBackReference 是引用的后面部分——它将从序列化中省略。

所以不要尝试使用@JsonBackReference：@JsonManagedReference。

希望这能解决您的问题。