当json包含type属性时，jackson能否确定要反序列化的根对象类型？ [英] Can jackson determine root object type to deserialize to when json includes type property?

问题描述

假设序列化为json包含实际对象的类名，在类上使用此注释：

Assume serialization to json includes the class name of the actual object, using this annotation on the Class:

@JsonTypeInfo(use = JsonTypeInfo.Id.CLASS, include = JsonTypeInfo.As.PROPERTY, property = "@type")
class MyClass {
    String foo;
}

所以json是例如：

{"@type": "com.example.MyClass", "foo": "bar"}

这可以反序列化而不指定类型吗？我的意思是甚至不是超级型。就像这样：

Can this be deserialized without specifying the type? And I mean not even the super type. Just something like:

objectMapper.readValue(value, Object.class);

这实际上不起作用，它会带回一张地图。

which doesn't actually work, it brings back a Map.

推荐答案

嗯，这当然可以做到这一点，尽管我个人从未使用过杰克逊。您可以将其反序列化为 JsonNode 对象，然后将其转换为正确的类型。

Well, it is certainly possible to do that although I have personally never used Jackson that way. You can deserialize it to a JsonNode object and then convert it to the proper type.

final ObjectMapper objectMapper = new ObjectMapper();
final MyClass myClass = new MyClass();
myClass.foo = "bar";

// Serialize
final String json = objectMapper.writeValueAsString(myClass);

// Deserialize
final JsonNode jsonNode = objectMapper.readTree(json);

// Get the @type
final String type = jsonNode.get("@type").asText();

// Create a Class-object
final Class<?> cls = Class.forName(type);

// And convert it
final Object o = objectMapper.convertValue(jsonNode, cls);

System.out.println(o.getClass());

输出为：

MyClass

MyClass

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