Java Jackson - @JsonTypeInfo 属性被映射为 null？
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Hymanson - @JsonTypeInfo property is being mapped as null?
提问by jscherman
I have this response:
我有这样的回应：
{
"id":"decaa828741611e58bcffeff819cdc9f",
"statement":"question statement",
"exercise_type":"QUESTION"
}
Then, based on exercise_typeattribute, I want to instantiate different objects instances (subclasses of ExerciseResponseDTO), so I create this mix in:
然后，基于运动类型属性，我想实例化不同的对象实例（ 的子类ExerciseResponseDTO），所以我创建了这个混合：
@JsonTypeInfo(
use = JsonTypeInfo.Id.NAME,
include = JsonTypeInfo.As.PROPERTY,
property = "exercise_type")
@JsonSubTypes({
@Type(value = ExerciseChoiceResponseDTO.class, name = "CHOICE"),
@Type(value = ExerciseQuestionResponseDTO.class, name = "QUESTION")})
public abstract class ExerciseMixIn
{}
public abstract class ExerciseResponseDTO {
private String id;
private String statement;
@JsonProperty(value = "exercise_type") private String exerciseType;
// Getters and setters
}
public class ExerciseQuestionResponseDTO
extends ExerciseResponseDTO {}
public class ExerciseChoiceResponseDTO
extends ExerciseResponseDTO {}
So I create my ObjectMapperas follows
所以我创建我ObjectMapper的如下
ObjectMapper mapper = new ObjectMapper();
mapper.addMixIn(ExerciseResponseDTO.class, ExerciseMixIn.class);
My test:
我的测试：
ExerciseResponseDTO exercise = mapper.readValue(serviceResponse, ExerciseResponseDTO.class)
Assert.assertTrue(exercise.getClass() == ExerciseQuestionResponseDTO.class); // OK
Assert.assertEquals("decaa828741611e58bcffeff819cdc9f" exercise.getId()); // OK
Assert.assertEquals("question statement", exercise.getStatement()); // OK
Assert.assertEquals("QUESTION", exercise.getExerciseType()); // FAIL. Expected: "QUESTION", actual: null
The problem is that, for some reason, the exercise_typeattribute being used as property on @JsonTypeInfois being mapped as null.
Any idea how i can solve this?
问题是，由于某种原因，用作属性 on的运动类型属性@JsonTypeInfo被映射为null。知道我该如何解决这个问题吗？
采纳答案by jscherman
Finally, I've found the solution in the API Doc
最后，我在API Doc 中找到了解决方案
Note on visibility of type identifier: by default, deserialization (use during reading of JSON) of type identifier is completely handled by Hymanson, and is not passed to deserializers. However, if so desired, it is possible to define property visible = true in which case property will be passed as-is to deserializers (and set via setter or field) on deserialization.
关于类型标识符可见性的注意事项：默认情况下，类型标识符的反序列化（在读取 JSON 期间使用）完全由 Hymanson 处理，不会传递给反序列化器。但是，如果需要，可以定义属性 visible = true 在这种情况下，属性将在反序列化时按原样传递给反序列化器（并通过 setter 或字段设置）。
So the solution was simply adding the 'visible' attribute as follows
所以解决方案只是简单地添加“可见”属性如下
@JsonTypeInfo(
use = JsonTypeInfo.Id.NAME,
include = JsonTypeInfo.As.PROPERTY,
property = "exercise_type",
visible = true)
@JsonSubTypes({
@Type(value = ExerciseChoiceResponseDTO.class, name = "CHOICE"),
@Type(value = ExerciseQuestionResponseDTO.class, name = "QUESTION")})
public abstract class ExerciseMixIn
{}
Hope this helps someone else.
希望这对其他人有帮助。
回答by Shashank
As per @jscherman answerby setting, 'visible' true in JsonTypeInfo will help in accessing exercise_type as a field.
根据@jscherman通过设置回答，JsonTypeInfo 中的'visible' true 将有助于将运动类型作为字段访问。
If you use the same class to serialize also then resulting JSON will have exercise_type appear twice. So it's better to also update include to JsonTypeInfo.As.EXISTING_PROPERTY
如果您也使用相同的类进行序列化，那么生成的 JSON 将出现两次运动类型。所以最好也更新包含到JsonTypeInfo.As.EXISTING_PROPERTY
And it's also worth looking at all other optionsfor include.
并且还值得查看包含的所有其他选项。
