对包含混合子类型多态性的映射进行反序列化/序列化时，缺少属性“type”

Question

我有一个名为Animal的对象，有两个子类，Monkey和Lion，我使用JsonTypeInfo来支持子类型检测，我认为在序列化JsonTypeInfo时，应该根据类自动放置名为“type”的属性。

动物类

import java.io.Serializable;
import com.fasterxml.jackson.annotation.JsonSubTypes;
import com.fasterxml.jackson.annotation.JsonTypeInfo;

@JsonTypeInfo(use = JsonTypeInfo.Id.NAME, property = "type")
@JsonSubTypes({
        @JsonSubTypes.Type(value = Lion.class, name = "Lion"),
        @JsonSubTypes.Type(value = Monkey.class, name = "Monkey")
})
public class Animal implements Serializable {
    
    String name;

    public Animal(String name) {
        super();
        this.name = name;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    @Override
    public int hashCode() {
        final int prime = 31;
        int result = 1;
        result = prime * result + ((name == null) ? 0 : name.hashCode());
        return result;
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj)
            return true;
        if (obj == null)
            return false;
        if (getClass() != obj.getClass())
            return false;
        Animal other = (Animal) obj;
        if (name == null) {
            if (other.name != null)
                return false;
        } else if (!name.equals(other.name))
            return false;
        return true;
    }

}

狮子级

public class Lion extends Animal{

    public Lion(String name) {
        super(name);
    }

}

猴子班

public class Monkey extends Animal{

    public Monkey(String name) {
        super(name);
    }

}

主要功能

    public static void main(String[] args) throws JsonGenerationException, JsonMappingException, IOException {
        Map<String,Animal> animals = new HashMap<String, Animal>();
        animals.put("Bob", new Lion("Bob"));
        animals.put("Alice", new Monkey("Alice"));
        StringWriter sw = new StringWriter();
        ObjectMapper mapper = new ObjectMapper();
        mapper.setSerializationInclusion(Include.NON_NULL);
        mapper.writeValue(sw, animals);
        String animlasStr = sw.toString();
        Map<String,Animal> dAnimalMap = mapper.readValue(animlasStr, new TypeReference<Map<String, Animal>>() {});
        assert dAnimalMap.get("Alice") instanceof Monkey;
    }

但当我反序列化动物地图时，它就不起作用了！！，它引发以下异常，类型属性缺失。

 com.fasterxml.jackson.databind.JsonMappingException: Unexpected token (END_OBJECT), expected FIELD_NAME: missing property 'type' that is to contain type id  (for class ....Animal)
 at [Source: {"Bob":{"name":"Bob"},"Alice":{"name":"Alice"}}

我尝试了类型引用和可见属性，得到了相同的结果。

@JsonTypeInfo(use = JsonTypeInfo.Id.NAME, property = "type" , visible =true)

Answer 1

而不是：mapper.writeValue（sw，动物）；使用mapper.writerFor（new Type参考

而不是：mapper.readValue（AnimlasStr，新的Type参考

所有类中都有空构造函数