Jackson实现多态性JSON反序列化：处理动态类型键值

{"type":"dog", "name":"bulli", "barkVolume":10}
{"type":"cat", "name":"kitty", "likesCream":true}

{"bulli":"dog","barkVolume":10}
{"dogi":"dog", "barkVolume":7}
{"kitty":"cat", "likesCream":true, "lives":3}
{"milkey":"cat", "likesCream":false, "lives":9}

import com.fasterxml.jackson.annotation.JsonIgnoreProperties;
import com.fasterxml.jackson.annotation.JsonProperty;
import com.fasterxml.jackson.databind.annotation.JsonDeserialize;

// 使用自定义反序列化器处理Animal类型
@JsonDeserialize(using = AnimalDeserializer.class)
// 忽略JSON中未映射到Java对象属性的字段，以防止解析错误
@JsonIgnoreProperties(ignoreUnknown = true)
public abstract class Animal {
    public String name; // 动物的名称
}

public class Dog extends Animal {
    @JsonProperty("barkVolume") // 映射JSON字段到Java属性
    public int barkVolume; // 狗的吠叫音量
}

public class Cat extends Animal {
    @JsonProperty("likesCream") // 映射JSON字段到Java属性
    public boolean likesCream; // 猫是否喜欢奶油
    @JsonProperty("lives") // 映射JSON字段到Java属性
    public int lives; // 猫的生命次数
}

import com.fasterxml.jackson.core.JsonParser;
import com.fasterxml.jackson.databind.DeserializationContext;
import com.fasterxml.jackson.databind.JsonDeserializer;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.node.ObjectNode;

import java.io.IOException;
import java.util.Iterator;
import java.util.Map;

public class AnimalDeserializer extends JsonDeserializer<Animal> {

    @Override
    public Animal deserialize(JsonParser jsonParser, DeserializationContext deserializationContext) throws IOException {
        // 获取当前的ObjectMapper实例，用于后续的JSON节点操作
        ObjectMapper mapper = (ObjectMapper) jsonParser.getCodec();
        // 将当前JSON对象读取为ObjectNode，方便遍历和操作
        ObjectNode node = mapper.readTree(jsonParser);

        // 遍历JSON对象的所有字段（键值对）
        Iterator<Map.Entry<String, com.fasterxml.jackson.databind.JsonNode>> fields = node.fields();
        while (fields.hasNext()) {
            Map.Entry<String, com.fasterxml.jackson.databind.JsonNode> field = fields.next();
            String fieldName = field.getKey(); // 获取字段名 (例如 "bulli", "kitty")
            String fieldValue = field.getValue().asText(); // 获取字段值 (例如 "dog", "cat")

            // 根据字段值判断动物类型
            if (fieldValue.equalsIgnoreCase("dog")) {
                // 如果是"dog"类型，则将整个JSON节点映射为Dog对象
                Dog dog = mapper.treeToValue(node, Dog.class);
                dog.name = fieldName; // 将动态的字段名设置为Dog对象的name属性
                return dog;
            } else if (fieldValue.equalsIgnoreCase("cat")) {
                // 如果是"cat"类型，则将整个JSON节点映射为Cat对象
                Cat cat = mapper.treeToValue(node, Cat.class);
                cat.name = fieldName; // 将动态的字段名设置为Cat对象的name属性
                return cat;
            }
        }
        // 如果遍历完所有字段仍未找到匹配的动物类型，则抛出异常
        throw new IllegalArgumentException("无法识别的动物类型: " + node.toString());
    }
}

import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.core.type.TypeReference;
import com.fasterxml.jackson.databind.ObjectMapper;

import java.util.List;

public class Farm {

    private static final String json = "[" +
        "{\"bulli\":\"dog\",\"barkVolume\":10},\n" +
        "{\"dogi\":\"dog\", \"barkVolume\":7},\n" +
        "{\"kitty\":\"cat\", \"likesCream\":true, \"lives\":3},\n" +
        "{\"milkey\":\"cat\", \"likesCream\":false, \"lives\":9}" +
        "]";

    public static void main(String[] args) throws JsonProcessingException {
        ObjectMapper mapper = new ObjectMapper();
        // 使用TypeReference处理泛型列表的反序列化
        List<Animal> animals = mapper.readValue(json, new TypeReference<List<Animal>>() {});

        System.out.println("反序列化结果：");
        animals.forEach(a -> {
            System.out.println("--------------------");
            System.out.println("动物名称: " + a.name);
            if (a instanceof Dog) {
                Dog dog = (Dog) a;
                System.out.println("动物类型: 狗");
                System.out.println("吠叫音量: " + dog.barkVolume);
            } else if (a instanceof Cat) {
                Cat cat = (Cat) a;
                System.out.println("动物类型: 猫");
                System.out.println("喜欢奶油: " + cat.likesCream);
                System.out.println("生命次数: " + cat.lives);
            }
        });
    }
}

反序列化结果：
--------------------
动物名称: bulli
动物类型: 狗
吠叫音量: 10
--------------------
动物名称: dogi
动物类型: 狗
吠叫音量: 7
--------------------
动物名称: kitty
动物类型: 猫
喜欢奶油: true
生命次数: 3
--------------------
动物名称: milkey
动物类型: 猫
喜欢奶油: false
生命次数: 9