Jackson 通过字段进行多态反序列化

Question

比方说，我有一个 class

public class A{
  private UUID typeId;
  private B data;
}

public abstract class B{
  private String a;
}

public class BChildOne extends B{
  ... some variables
}

public class BChildTwo  extends B{
  ... some variables
}

B的class类型根据A的typeId在变化，所以如果A的typeId是"XXX"，数据字段的类型是BChildOne，如果A的typeId是"YYY", 数据字段类型为 BChildTwo.

我怎样才能做到这一点？

所以我试过了；

@JsonAutoDetect(fieldVisibility = JsonAutoDetect.Visibility.ANY, getterVisibility =
JsonAutoDetect.Visibility.NONE, setterVisibility = 
JsonAutoDetect.Visibility.NONE)
@JsonIgnoreProperties(ignoreUnknown = true)
@JsonTypeInfo(use = JsonTypeInfo.Id.NAME, include = 
JsonTypeInfo.As.EXTERNAL_PROPERTY , property = "typeId")
@JsonSubTypes({
 @JsonSubTypes.Type(value = BChildOne.class, name = "40ad2fe6-e672-4f0e- 
986e- 
 619c7a1a3223") }
 )
 public abstract class B{

但是我遇到了以下错误；

Unexpected token (END_OBJECT), expected FIELD_NAME: missing property 'typeId' that is to contain type id (for class B)

这很明显，因为 typeId 字段在 class A 而不是 B。

Answer 1

我曾经遇到过同样的序列化问题，我做了一个这样的实现。请参阅下面的代码。

    protected Entity serialize(Object entity) throws Exception {
    try {
        if ( entity instanceof AbstractProcessRequest ) {
            AbstractProcessRequest request = (AbstractProcessRequest) entity;
            String value = mapper.writeValueAsString(request.prepareJSONRequest());
            logger.info("Telesales String json request " + value);
            return new Entity(value, UTF_8);
        } else {
            String value = mapper.writeValueAsString(entity);
            return new StringEntity(value, UTF_8);
        }
    } catch (Exception e) {
        logger.error("Telesales --> Error occured serializing entity", e);
        throw e;
    }
}

为了实现通用结构，在某些服务中创建了一个执行方法 class，如下所示。

private <T> T execute(Object entity, Class<T> clazz, HttpRequestBase request, String contentType) throws Exception {

Answer 2

假设您的 JSON 文档如下：

{
  "type": "foo",
  "data": {
    "someCommonProperty": "common property",
    "fooProperty": "foo specific property"
  }
}

{
  "type": "bar",
  "data": {
    "someCommonProperty": "common property",
    "barProperty": "bar specific property"
  }
}

您可以使用：

public class Wrapper {

    private String type;

    @JsonTypeInfo(use = Id.NAME, property = "type", include = As.EXTERNAL_PROPERTY)
    @JsonSubTypes(value = { 
        @JsonSubTypes.Type(value = Foo.class, name = "foo"),
        @JsonSubTypes.Type(value = Bar.class, name = "bar") 
    })
    private AbstractData data;

    // Getters and setters
}

public abstract class AbstractData {

    private String someCommonProperty;

    // Getters and setters
}

public class Foo extends AbstractData {

    private String fooProperty;

    // Getters and setters
}

public class Bar extends AbstractData {

    private String barProperty;

    // Getters and setters
}

在这个方法中，@JsonTypeInfo is set to use type as an external property确定对class映射data属性。 JSON 文档可以反序列化如下：

ObjectMapper mapper = new ObjectMapper();
Wrapper wrapper = mapper.readValue(json, Wrapper.class);

Jackson 通过字段进行多态反序列化

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