Jackson无法识别父类字段：子类反序列化报错问题

问题场景 #

使用Lombok的@Builder和Jackson的@Jacksonized注解实现父类Parent与子类Child的序列化/反序列化时，执行测试用例抛出UnrecognizedPropertyException，提示父类的recipient字段在Child$ChildRequestBuilder中不被识别。

Parent父类代码 #

@Builder
@Jacksonized
@EqualsAndHashCode
@ToString
@Getter
@Setter
@JsonInclude(JsonInclude.Include.NON_NULL)
@AllArgsConstructor
@NoArgsConstructor
@JsonTypeInfo(use = DEDUCTION)
@JsonSubTypes({
        @JsonSubTypes.Type(value = Child.class, name = "Child")
})
public class Parent implements Serializable {

    private static final long serialVersionUID = 6223930820946596247L;

    @JsonProperty("recipient")
    protected Recipient recipient;
    
    // 其他字段和方法
}

Child子类代码 #

@Builder(builderMethodName = "childRequestBuilder")
@Jacksonized
@EqualsAndHashCode
@ToString
@Getter
@Setter
@AllArgsConstructor
@NoArgsConstructor
@JsonInclude(JsonInclude.Include.NON_NULL)
public class Child extends Parent implements Serializable {

    private static final long serialVersionUID = -2848064640409441165L;

    @JsonProperty("use_case")
    private String useCase;
}

异常信息 #

com.fasterxml.jackson.databind.exc.UnrecognizedPropertyException:
Unrecognized field "recipient" (class a.b.Child$ChildRequestBuilder),
not marked as ignorable (1 known properties: "use_case"]) at [Source:
(String)"{"recipient":{"endpoint_details":{"someToken":"someToken","someDevice":"someDevice","someApp":"someApp"}}}";;
line: 1, column: 129] (through reference chain:
a.b.Child$ChildRequestBuilder["recipient"])

测试代码 #

@Test
public void testChildDeserialization() throws JsonProcessingException {
    SomeEndPoint endPoint = SomeEndpoint.builder()
            .someToken("someToken")
            .someDevice("someDevice")
            .someApp("someApp")
            .build();
    Recipient recipient = Recipient.builder().endpointDetails(endPoint).build();
    Child child = Child.childRequestBuilder().build();
    child.setRecipient(recipient);
    String request = new ObjectMapper().writeValueAsString(child);
    Child deserialisedChild = new ObjectMapper().readValue(request, Child.class);
    SomeEndPoint someEndPoint = (SomeEndPoint) deserialisedChild.getRecipient().getEndpointDetails();
    Assert.assertEquals(someEndPoint.getSomeToken(), endPoint.getSomeToken());
}

解决方案 #

核心原因 #

普通的@Builder注解不会自动将父类字段继承到子类的Builder中，而@Jacksonized在反序列化时会尝试通过Builder构建对象，导致父类字段无法被Builder识别，从而抛出异常。

具体修复步骤 #

1. 替换普通@Builder为@SuperBuilder
   父类和子类都需要使用Lombok的@SuperBuilder注解（要求Lombok版本≥1.18.16），该注解专门处理继承场景下的Builder模式，会自动将父类字段继承到子类Builder中。

   • 修改Parent类的@Builder为@SuperBuilder
   • 修改Child类的@Builder为@SuperBuilder

   修改后的Parent类代码：

   @SuperBuilder
   @Jacksonized
   @EqualsAndHashCode
   @ToString
   @Getter
   @Setter
   @JsonInclude(JsonInclude.Include.NON_NULL)
   @AllArgsConstructor
   @NoArgsConstructor
   @JsonTypeInfo(use = DEDUCTION)
   @JsonSubTypes({
           @JsonSubTypes.Type(value = Child.class, name = "Child")
   })
   public class Parent implements Serializable {
       // 字段和其他内容不变
   }
   

   修改后的Child类代码：

   @SuperBuilder(builderMethodName = "childRequestBuilder")
   @Jacksonized
   @EqualsAndHashCode
   @ToString
   @Getter
   @Setter
   @AllArgsConstructor
   @NoArgsConstructor
   @JsonInclude(JsonInclude.Include.NON_NULL)
   public class Child extends Parent implements Serializable {
       // 字段和其他内容不变
   }
   

2. 优化测试代码（可选但推荐）
   修复后可直接通过Builder设置父类字段，无需手动调用setter方法，更符合Builder模式设计：

   @Test
   public void testChildDeserialization() throws JsonProcessingException {
       SomeEndPoint endPoint = SomeEndpoint.builder()
               .someToken("someToken")
               .someDevice("someDevice")
               .someApp("someApp")
               .build();
       Recipient recipient = Recipient.builder().endpointDetails(endPoint).build();
       // 直接通过Builder设置父类的recipient字段
       Child child = Child.childRequestBuilder()
               .recipient(recipient)
               .build();
       String request = new ObjectMapper().writeValueAsString(child);
       Child deserialisedChild = new ObjectMapper().readValue(request, Child.class);
       SomeEndPoint someEndPoint = (SomeEndPoint) deserialisedChild.getRecipient().getEndpointDetails();
       Assert.assertEquals(someEndPoint.getSomeToken(), endPoint.getSomeToken());
   }
   

3. 备选方案（不推荐）
   若无法升级Lombok版本使用@SuperBuilder，可手动在Child的Builder中添加父类字段的设置方法，但需手动维护，容易遗漏或出错：

   public class Child extends Parent implements Serializable {
       // 字段不变
       
       public static class ChildRequestBuilder extends Parent.ParentBuilder<Child, ChildRequestBuilder> {
           private String useCase;
           
           public ChildRequestBuilder useCase(String useCase) {
               this.useCase = useCase;
               return this;
           }
           
           @Override
           public Child build() {
               Child child = new Child();
               child.setRecipient(this.recipient);
               child.setUseCase(this.useCase);
               return child;
           }
       }
       
       public static ChildRequestBuilder childRequestBuilder() {
           return new ChildRequestBuilder();
       }
   }
   

内容的提问来源于stack exchange，提问作者Arnav Sengupta