Jackson反序列化抽象类

Question

我正在尝试使用JSON ObjectMapper反序列化对象。我在尝试反序列化时看到以下错误

Answer 1

是的，您可以为抽象类编写自己的自定义反序列化程序。这个反序列化器必须确定JSON表示哪个具体类，并实例化它的一个实例。

这可能有一种更惯用的方法,但这里有一个简单的示例：

public class Test {
    public static void main(String... args) throws IOException {
        final ObjectMapper mapper = new ObjectMapper();
        final SimpleModule module = new SimpleModule();
        module.addDeserializer(Animal.class, new AnimalDeserializer());
        mapper.registerModule(module);

        final String json = "{\"aGoodBoy\": true}";
        final Animal animal = mapper.readValue(json, Animal.class);
        System.out.println(animal.talk());
    }

    public static abstract class Animal {
        public abstract String talk();
    }

    public static class Fish extends Animal {
        @Override
        public String talk() {
            return "blub blub I'm a dumb fish";
        }
    }

    public static class Dog extends Animal {
        public boolean aGoodBoy;

        @Override
        public String talk() {
            return "I am a " + (aGoodBoy ? "good" : "bad") + " dog";
        }
    }

    public static class AnimalDeserializer extends StdDeserializer<Animal> {
        protected AnimalDeserializer() {
            this(null);
        }

        protected AnimalDeserializer(final Class<?> vc) {
            super(vc);
        }

        @Override
        public Animal deserialize(final JsonParser parser, final DeserializationContext context)
        throws IOException, JsonProcessingException {
            final JsonNode node = parser.getCodec().readTree(parser);
            final ObjectMapper mapper = (ObjectMapper)parser.getCodec();
            if (node.has("aGoodBoy")) {
                return mapper.treeToValue(node, Dog.class);
            } else {
                return mapper.treeToValue(node, Fish.class);
            }
        }
    }
}