Question

我正在使用

@JsonTypeInfo(use=JsonTypeInfo.Id.CLASS, include=JsonTypeInfo.As.PROPERTY,
              property="_class")
class Base { }
class Derived1 extends Base { ... }
class Derived2 extends Base { ... }
...

序列化和反序列化多态基类。这很好但我被迫在我的JSON文档中包含_class属性，即使在编译时已知实际类型的地方也是如此。我有很多Derived类（其中没有一个是多态的）和许多我无法控制的JSON文档，所以如果声明的类实际上是Base，我想使用动态类型信息。

这可能与杰克逊有关吗？例如，我希望以下工作：

package json_demo;
import com.fasterxml.jackson.annotation.JsonTypeInfo;
import com.fasterxml.jackson.databind.ObjectMapper;
@JsonTypeInfo(use=JsonTypeInfo.Id.CLASS,
              include=JsonTypeInfo.As.PROPERTY, property="_class")
class Base {
   public int baseMember_;
}
class Derived extends Base {
   public int derivedMember_;
}
class Demo {
   public Derived member_;
}
public class Main
{
   public static void main( String[] args ) throws Exception
   {
      final String input = "{ \"member_\": { \"baseMember_\":1," 
                         + "\"derivedMember_\":2 } }";
      ObjectMapper mapper = new ObjectMapper();
      mapper.readValue(input, Demo.class);  // throws, why?
   }
}

我从readValue（）获得的异常是

JsonMappingException:
Unexpected token (END_OBJECT), expected FIELD_NAME:
missing property '_class' that is to contain type id 
(for class json_demo.Derived)

Answer 1

它说“缺少属性'_class'”，那么json字符串应该是这样的：

{
    "member_": {
        "_class": "json_demo.Derived",
        "baseMember_": 1,
        "derivedMember_": 2
    }
}

杰克逊：混合静态/动态类型处理

1 个答案: