java-杰克逊反序列化抽象类

com.fasterxml.jackson.databind.JsonMappingException: Can not construct
instance of com.phoenix.types.OrderItem:
abstract types either need to be mapped to concrete types, have custom
deserializer, or contain additional type information at [Source:
java.io.StringReader@4bb33f74; line: 112, column: 7] (through
reference chain:
com.phoenix.types.GenerateRequest[“order”]->com.phoenix.types.Order[“orderItems”]->Object[][0])
at
com.fasterxml.jackson.databind.JsonMappingException.from(JsonMappingException.java:261)
at
com.fasterxml.jackson.databind.DeserializationContext.instantiationException(DeserializationContext.java:1456)
at
com.fasterxml.jackson.databind.DeserializationContext.handleMissingInstantiator(DeserializationContext.java:1012)
at
com.fasterxml.jackson.databind.deser.AbstractDeserializer.deserialize(AbstractDeserializer.java:149)
at
com.fasterxml.jackson.databind.deser.std.ObjectArrayDeserializer.deserialize(ObjectArrayDeserializer.java:196)
at
com.fasterxml.jackson.databind.deser.std.ObjectArrayDeserializer.deserialize(ObjectArrayDeserializer.java:20)
at
com.fasterxml.jackson.databind.deser.SettableBeanProperty.deserialize(SettableBeanProperty.java:499)
at
com.fasterxml.jackson.databind.deser.impl.MethodProperty.deserializeAndSet(MethodProperty.java:101)
at
com.fasterxml.jackson.databind.deser.BeanDeserializer.vanillaDeserialize(BeanDeserializer.java:276)
at
com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:140)
at
com.fasterxml.jackson.databind.deser.SettableBeanProperty.deserialize(SettableBeanProperty.java:499)
at
com.fasterxml.jackson.databind.deser.impl.MethodProperty.deserializeAndSet(MethodProperty.java:101)
at
com.fasterxml.jackson.databind.deser.BeanDeserializer.vanillaDeserialize(BeanDeserializer.java:276)
at
com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:140)
at
com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:3789)
at
com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:2833)

我遇到了执行多态反序列化的post.这基本上为解决上面列出的错误提供了解决方案.我用于反序列化的类(在这种情况下为OrderItem等)是jar文件的一部分.但是,有一种方法可以在尝试反序列化时将JsonDeserialize定义为objectmapper的一部分,而不是在类本身中添加注释,因为我无法访问它.

可能有一种更惯用的方法,但这是一个简单的示例：

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);
            }
        }
    }
}