仅当存在某些字段时才使用自定义JSON反序列化(使用Jackson) [英] Custom JSON deserialization only if certain field is present (using Jackson)

问题描述

反序列化MyEntity(这是一个接口)时，我要么拥有

When deserializing MyEntity (which is an interface) I either have

• 以下输入:

• the following input:

{ "id": 123 }

在这种情况下，我想将其反序列化为

in which case I would like to deserialize it into a

new MyEntityRef(123)

或者我输入以下内容:

or I have the following input:

{
    "id": 123,
    "message": "Hello world",
    "otherEntity": {
        "field": "value",
        ...
    }
}

在这种情况下，我想将其反序列化为

in which case I would like to deserialize it as

new MyEntityImpl(123, "Hello world", otherEntity);

其中otherEntity被反序列化的方式与在MyEntity上下文之外找到它的方式相同.

where otherEntity is deserialized the same way as if it was found outside the context of MyEntity.

我已经找到了如何通过SimpleModule注册自己的自定义反序列化器，但是我不知道如何

I've figured out how to register my own custom deserializer through a SimpleModule but I don't know how to

1. 根据某些字段(例如上面的message)的存在来选择自定义解串器.
2. 某些字段(例如上面的otherEntity)在默认"序列化程序上的回退.

1. Choose a custom deserializer based on the presense of some field (such as message above).
2. Fallback on the "default" serializer for certain fields (such as otherEntity above).

推荐答案

通过如下配置我的ObjectMapper最终解决了该问题:

Finally solved it by configuring my ObjectMapper as follows:

ObjectMapper mapper = new ObjectMapper();

SimpleModule idAsRefModule = new SimpleModule("ID-to-ref",
                                              new Version(1, 0, 0, null));

idAsRefModule.addDeserializer(TestEntity.class,
                              new JsonDeserializer<TestEntity>() {
    @Override
    public TestEntity deserialize(JsonParser jp, DeserializationContext dc)
            throws IOException, JsonProcessingException {

        ObjectCodec codec = jp.getCodec();
        JsonNode node = codec.readTree(jp);
        boolean isFullImpl = node.has("message");
        Class<? extends TestEntity> cls = isFullImpl ? TestEntityImpl.class
                                                     : TestEntityRef.class;
        return codec.treeToValue(node, cls);
    }
});

mapper.registerModule(idAsRefModule);

return mapper;

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