Question

TL; DR - 包含一个成员的包装类，该成员是一个用@JsonTypeInfo注释的抽象类的列表。

我有一个包装类和一个带有根抽象类的类层次结构，一个子抽象类和一个具体的孙子。

public static class RootClassWrapper {
    public static final String JSON_KEY_ROOT_CLASS_LIST =
        "root_class_list";

    @JsonProperty(JSON_KEY_ROOT_CLASS_LIST)
    private final List<RootClass> rootClassList;

    @JsonCreator
    public RootClassWrapper(
        @JsonProperty(JSON_KEY_ROOT_CLASS_LIST)
            final List<RootClass> rootClassList) {

        this.rootClassList = rootClassList;
    }
}

@JsonTypeInfo(
    use = JsonTypeInfo.Id.NAME,
    include = JsonTypeInfo.As.PROPERTY,
    property = RootClass.JSON_KEY_ROOT_CLASS_TYPE)
@JsonSubTypes({
    @JsonSubTypes.Type(
        value = GrandchildClass.class,
        name = GrandchildClass.CHILD_CLASS_TYPE) })
public static abstract class RootClass {
    public static final String JSON_KEY_ROOT_CLASS_TYPE = "root_class_type";
    public static final String JSON_KEY_ID = "id";

    @JsonProperty(JSON_KEY_ID)
    private final String id;

    @JsonCreator
    public RootClass(
        @JsonProperty(JSON_KEY_ID) final String id) {

        this.id = id;
    }
}

public static abstract class ChildClass extends RootClass {
    @JsonCreator
    public ChildClass(
        @JsonProperty(JSON_KEY_ID) final String id) {

        super(id);
    }
}

public static class GrandchildClass extends ChildClass {
    public static final String CHILD_CLASS_TYPE = "grandchild";

    @JsonCreator
    public GrandchildClass(
        @JsonProperty(JSON_KEY_ID) final String id) {

        super(id);
    }
}

尝试使用此层次结构：

ByteArrayOutputStream out = new ByteArrayOutputStream();
GrandchildClass grandchildClass = new GrandchildClass("grandchildId");
List<RootClass> rootClassList = new ArrayList<RootClass>(1);
rootClassList.add(grandchildClass);
RootClassWrapper wrapper = new RootClassWrapper(rootClassList);
mapper.writeValue(out, wrapper);
System.out.println(out.toString());

RootClassWrapper rootClassWrapper =
    mapper.readValue(out.toString(), RootClassWrapper.class);
mapper.writeValue(System.out, rootClassWrapper);

对象可以序列化，System.out.println(out.toString());可以观察到：

{"root_class_list":[{"root_class_type":"grandchild","id":"grandchildId"}]}

但是同一输出的反序列化会导致以下错误：

Exception in thread "main" com.fasterxml.jackson.databind.JsonMappingException: Could not find creator property with name 'id' (in class test.Test$RootClass)
    at [Source: java.io.StringReader@13de68e2; line: 1, column: 1]
       at com.fasterxml.jackson.databind.JsonMappingException.from(JsonMappingException.java:164)
       at com.fasterxml.jackson.databind.DeserializationContext.mappingException(DeserializationContext.java:584)
       at com.fasterxml.jackson.databind.deser.BeanDeserializerFactory.addBeanProps(BeanDeserializerFactory.java:551)
       at com.fasterxml.jackson.databind.deser.BeanDeserializerFactory.buildBeanDeserializer(BeanDeserializerFactory.java:267)
       at com.fasterxml.jackson.databind.deser.BeanDeserializerFactory.createBeanDeserializer(BeanDeserializerFactory.java:168)
       at com.fasterxml.jackson.databind.deser.DeserializerCache._createDeserializer2(DeserializerCache.java:405)
       at com.fasterxml.jackson.databind.deser.DeserializerCache._createDeserializer(DeserializerCache.java:354)
       at com.fasterxml.jackson.databind.deser.DeserializerCache._createAndCache2(DeserializerCache.java:267)
       at com.fasterxml.jackson.databind.deser.DeserializerCache._createAndCacheValueDeserializer(DeserializerCache.java:247)
       at com.fasterxml.jackson.databind.deser.DeserializerCache.findValueDeserializer(DeserializerCache.java:146)
       at com.fasterxml.jackson.databind.DeserializationContext.findContextualValueDeserializer(DeserializationContext.java:305)
       at com.fasterxml.jackson.databind.deser.std.CollectionDeserializer.createContextual(CollectionDeserializer.java:151)
       at com.fasterxml.jackson.databind.deser.std.CollectionDeserializer.createContextual(CollectionDeserializer.java:23)
       at com.fasterxml.jackson.databind.DeserializationContext.findContextualValueDeserializer(DeserializationContext.java:309)
       at com.fasterxml.jackson.databind.deser.impl.PropertyBasedCreator.construct(PropertyBasedCreator.java:96)
       at com.fasterxml.jackson.databind.deser.BeanDeserializerBase.resolve(BeanDeserializerBase.java:414)
       at com.fasterxml.jackson.databind.deser.DeserializerCache._createAndCache2(DeserializerCache.java:298)
       at com.fasterxml.jackson.databind.deser.DeserializerCache._createAndCacheValueDeserializer(DeserializerCache.java:247)
       at com.fasterxml.jackson.databind.deser.DeserializerCache.findValueDeserializer(DeserializerCache.java:146)
       at com.fasterxml.jackson.databind.DeserializationContext.findRootValueDeserializer(DeserializationContext.java:322)
       at com.fasterxml.jackson.databind.ObjectMapper._findRootDeserializer(ObjectMapper.java:2990)
       at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:2884)
       at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:2034)
       at test.Test.main(Test.java:130)

Answer 1

还有一个错误，但这可行

为RootClass创建一个私有的默认构造函数，用@JsonCreator标记它，并从现有构造函数中删除注释似乎有效。中间抽象类的@JsonCreator注释是无关紧要的。

@JsonTypeInfo(
    use = JsonTypeInfo.Id.NAME,
    include = JsonTypeInfo.As.PROPERTY,
    property = RootClass.JSON_KEY_ROOT_CLASS_TYPE)
@JsonSubTypes({
    @JsonSubTypes.Type(
        value = GrandchildClass.class,
        name = GrandchildClass.CHILD_CLASS_TYPE) })
public static abstract class RootClass {
    public static final String JSON_KEY_ROOT_CLASS_TYPE = "root_class_type";
    public static final String JSON_KEY_ID = "id";

    @JsonProperty(JSON_KEY_ID)
    private final String id;

    @JsonCreator
    private RootClass() {
        id = null;
    }

    public RootClass(final String id) {
        this.id = id;
    }
}

public static abstract class ChildClass extends RootClass {

    /**
     * The annotations here don't matter.
     */
    @JsonCreator
    public ChildClass(@JsonProperty(JSON_KEY_ID) final String id) {
        super(id);
    }
}

public static class GrandchildClass extends ChildClass {
    public static final String CHILD_CLASS_TYPE = "grandchild";

    @JsonCreator
    public GrandchildClass(@JsonProperty(JSON_KEY_ID) final String id) {
        super(id);
    }
}

当子类具有成员且根类是包装类的成员时，JsonTypeInfo被破坏

1 个答案: