多级@JSONTypeInfo和@JSONSubtypes

Question

@JsonTypeInfo(use = JsonTypeInfo.Id.NAME, include = JsonTypeInfo.As.EXISTING_PROPERTY, property = "type")
@JsonSubTypes({@JsonSubTypes.Type(value = B.class, name = "B")})
public abstract class A {

    private final String type;

    public A(String type) {
        this.type = type;
    }
}

@JsonTypeInfo(use = JsonTypeInfo.Id.NAME, include = JsonTypeInfo.As.EXISTING_PROPERTY, property = "type2")
@JsonSubTypes({@JsonSubTypes.Type(value = C.class, name = "C")})
public class B extends A {

    private final String type2;

    private final String propertyB;

    @JsonCreator
    public B(@JsonProperty("type2") String type2,
             @JsonProperty("propertyB") String propertyB) {
        super("B");
        this.type2 = type2;
        this.propertyB = propertyB;
    }
}

public class C extends B {

    private final String propertyC;

    @JsonCreator
    public C(@JsonProperty("propertyB") String propertyB,
             @JsonProperty("propertyC") String propertyC) {
        super("C", propertyB);
        this.propertyC = propertyC;
    }
}

@Test
void whenReadCJsonToA_thenObjectIsInstanceOfC() throws JsonProcessingException {

    String json = "{\n" +
                  "  \"type\" : \"B\",\n" +
                  "  \"type2\" : \"C\",\n" +
                  "  \"propertyB\" : \"b\",\n" +
                  "  \"propertyC\" : \"c\"\n" +
                  "}";

    A obj = objectMapper.readValue(json, A.class);
    assertTrue(obj instanceof B, "obj is not instance of B");  // pass
    assertTrue(obj instanceof C, "obj is not instance of C");  // fail
}

我的maven项目可以在GitHub中找到。

Answer 1

根据Jackson的这个问题，只支持一个类型discliminator属性的多级继承。在我的代码中，只保留属性type并删除属性type2。

@JsonTypeInfo(use = JsonTypeInfo.Id.NAME, include = JsonTypeInfo.As.EXISTING_PROPERTY, property = "type")
@JsonSubTypes({@JsonSubTypes.Type(value = B.class, name = "B")})
public abstract class A {

    private final String type;

    public A(String type) {
        this.type = type;
    }
}

@JsonSubTypes({@JsonSubTypes.Type(value = C.class, name = "C")})
public class B extends A {

    private final String propertyB;

    @JsonCreator
    public B(@JsonProperty("propertyB") String propertyB) {
        super("B");
        this.propertyB = propertyB;
    }
}

public class C extends B {

    private final String propertyC;

    @JsonCreator
    public C(@JsonProperty("propertyB") String propertyB,
             @JsonProperty("propertyC") String propertyC) {
        super(propertyB);
        this.propertyC = propertyC;
    }
}

请参阅此提交中的完整代码。

此提交使用枚举作为类型discliminator属性类型。