具有泛型属性的类的Jackson序列化丢失泛型属性的类型信息

Question

当我使用Jackson ectivtMapper将有效负载序列化为字符串值时，我很难获取要维护的泛型属性的类型信息。

我想要达到的结果如下。

{"@type":"BlockChainWrapper","@id":1,"payload":{"@type":"TestClassA","@id":2,"helloWorld":"Hello World"},"nonce":255,"signature":"SGVsbG8gV29ybGQ="}

我实际得到的结果如下（注意TestClassA缺少@type信息）。

{"@type":"BlockChainWrapper","@id":1,"payload":{"@id":2,"helloWorld":"Hello World"},"nonce":255,"signature":"SGVsbG8gV29ybGQ="}

我使用的测试是：

class BlockChainWrapperTest extends Specification {

    def objectMapper = JacksonConfiguration.createObjectMapper()

    def "test Json marshalling"() {
        given: "A test payload"
        def payload = new BlockChainWrapper<TestClassA>(
                payload: new TestClassA(),
                nonce: 255,
                signature: "Hello World".getBytes(Charset.defaultCharset())
        )

        when:
        //ObjectWriter w = objectMapper.writerFor(new TypeReference<BlockChainWrapper<TestClassA>>() { });
        //def result = w.writeValueAsString(payload)
        def result = objectMapper.writeValueAsString(payload)

        then:
        assert result == "{\"@type\":\"BlockChainWrapper\",\"@id\":1,\"payload\":{\"@type\":\"TestClassA\",\"@id\":2,\"helloWorld\":\"Hello World\"},\"nonce\":255,\"signature\":\"SGVsbG8gV29ybGQ=\"}"
    }

    def "test TestClassA generates correct JSON"() {
        given:
        def payload = new TestClassA()

        when:
        def result = objectMapper.writeValueAsString(payload)

        then:
        assert result == "{\"@type\":\"TestClassA\",\"@id\":1,\"helloWorld\":\"Hello World\"}"
    }
}

“test JSON编组”测试中有两个版本。注释掉的版本和未注释的版本都会产生完全相同的结果。

第二个测试验证TestClassA本身是否生成了正确的类型信息。

只有当包含泛型类型的父类时，问题才会变成问题，随后会丢失类型信息，并导致反序列化返回TestClassA内容的LinkedHashMap。

TestClassA看起来像：

@JsonRootName("TestClassA")
@JsonTypeInfo(use = JsonTypeInfo.Id.NAME, property = "@type")
@JsonIdentityInfo(generator = ObjectIdGenerators.IntSequenceGenerator.class)
public class TestClassA implements Serializable {

    private String helloWorld = "Hello World";
}

泛型类如下所示：

@JsonRootName("BlockChainWrapper")
@JsonTypeInfo(use = JsonTypeInfo.Id.NAME, include= JsonTypeInfo.As.PROPERTY, property = "@type")
@JsonIdentityInfo(generator = ObjectIdGenerators.IntSequenceGenerator.class)
public class BlockChainWrapper<T> implements Serializable {

    private T payload;

为完整起见，Jackson ObjectMapper配置为

var mapper = new Jackson2ObjectMapperBuilder()
    .createXmlMapper(false)
    .modules(new JavaTimeModule(), new Jdk8Module())
    .serializationInclusion(JsonInclude.Include.NON_NULL)
    .build();
mapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
mapper.configure(JsonGenerator.Feature.WRITE_BIGDECIMAL_AS_PLAIN, true);
mapper.configure(DeserializationFeature.USE_BIG_DECIMAL_FOR_FLOATS, true);
mapper.configure(DeserializationFeature.READ_DATE_TIMESTAMPS_AS_NANOSECONDS, false);
mapper.configure(DeserializationFeature.ADJUST_DATES_TO_CONTEXT_TIME_ZONE, false);
mapper.configure(SerializationFeature.WRITE_DATE_TIMESTAMPS_AS_NANOSECONDS, false);
mapper.disable(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS);

Answer 1

我想我已经解决了你的问题。我已经用这个解决方案创建了一个github项目。https://github.com/GaetanoPiazzolla/stackoverflow-question-61025761

简而言之，您还应该在有效负载字段中添加@JsonTypeInfo注释：

@JsonTypeInfo(use=JsonTypeInfo.Id.NAME, include=JsonTypeInfo.As.PROPERTY, property="@type")
private T payload;