整数字段而不是字符串上的Jackson多态反序列化

Question

我熟悉常规的多态反序列化方法，即根据某个字段的字符串值反序列化对象。例如：

@JsonSubTypes(
          {
              @JsonSubTypes.Type(value = LionCage.class, name = "LION"),
              @JsonSubTypes.Type(value = TigerCage.class, name = "TIGER"),
          }
         )
@JsonTypeInfo(use = JsonTypeInfo.Id.NAME, include = JsonTypeInfo.As.PROPERTY, property = "type")

还有，我该怎么弄明白呢？看来应该是很明显的事情。

Answer 1

Jackson自动将字符串转换为数字，反之亦然。只需对数字使用字符串值即可。如1值的“1”。你自己试试（jackson版本是2.5.1):

import com.fasterxml.jackson.annotation.JsonSubTypes;
import com.fasterxml.jackson.annotation.JsonTypeInfo;
import com.fasterxml.jackson.databind.ObjectMapper;

public class HelloWorldJacksonNumber {

    public static class A extends Base {
        String a;
    }

    public static class B extends Base {
        String b;
    }

    @JsonTypeInfo(use = JsonTypeInfo.Id.NAME, property = "type")
    @JsonSubTypes({
            @JsonSubTypes.Type(value = A.class, name = "1"),
            @JsonSubTypes.Type(value = B.class, name = "2")})
    public static class Base {
        int type;
    }

    public static void main (String[] args) throws Exception {
        final ObjectMapper objectMapper = new ObjectMapper();
        System.out.println(objectMapper.version());

        System.out.println(objectMapper.writeValueAsString(new A()));
        System.out.println(objectMapper.writeValueAsString(new B()));

        System.out.println(objectMapper.readValue("{\"type\":\"1\"}", Base.class).getClass());
        System.out.println(objectMapper.readValue("{\"type\":\"2\"}", Base.class).getClass());
    }
}

输出为：

2.5.1
{"type":"1"}
{"type":"2"}
class HelloWorldJacksonNumber$A
class HelloWorldJacksonNumber$B