杰克逊为一个具有多态类型的字段定制解串器 [英] Jackson custom deserializer for one field with polymorphic types

问题描述

更新：

我尝试在jackson源代码中调试，并在方法中找出

I tried to debug in jackson source code and find out that in the method

反序列化（JsonParser jp，DeserializationContext ctxt） of

SettableBeanProperty.java

当 _valueTypeDeserializer 不为空时，它将永远不会使用 _valueDeserializer 。

when the _valueTypeDeserializer isn't null, it will never use _valueDeserializer.

这是一个正确的假设，TypeDeserializer应该比ValueDeserializer更合适吗？

Is this a correct assumption that TypeDeserializer should be more proper than ValueDeserializer?

我正在尝试使用 @JsonDeserialize 为一个具有多态类型的字段定义自定义反序列化器。我可以单独使用 @JsonDeserialize 和 @JsonTypeInfo 。但是当我一起使用它们时，似乎忽略了 @JsonDeserialize 注释。

I'm trying to use @JsonDeserialize to define custom deserializer for one field with polymorphic types. I can succeed to use @JsonDeserialize and @JsonTypeInfo seperately. But when i use them together, it seems that the @JsonDeserialize annotation is ignored.

这是我的类层次结构：

@JsonTypeInfo(use = JsonTypeInfo.Id.NAME, include = JsonTypeInfo.As.PROPERTY, property = "type", defaultImpl = Definition.class)
@JsonSubTypes({@Type(value = Definition.class, name = "normal"),
    @Type(value = FormDefinition.class, name = "form")})
public class Definition {

    private String name;
    private String description;

    // getter&setter for name&description
}

2. FormDefinition.java

2. FormDefinition.java

public class FormDefinition extends Definition {

    private String formName;
    @JsonDeserialize(using = DefinitionDeserializer.class)
    private Definition definition;

    public String getFormName() {
        return formName;
    }

    public void setFormName(String formName) {
        this.formName = formName;
    }

    public void setDefinition(Definition definition) {
        this.definition = definition;
    }
}

3。 DefinitionDeserializer.java

3. DefinitionDeserializer.java

public class DefinitionDeserializer extends JsonDeserializer<Definition> {

    @Override 
    public Definition deserialize(JsonParser jsonParser, DeserializationContext deserializationContext)
            throws IOException, JsonProcessingException {
        Definition definition = new Definition();
        String name = jsonParser.readValueAs(String.class);
        definition.setName(name);
        return definition;
    }
}

样本主

Sample main

public class App 
{
    public static void main( String[] args ) throws IOException {
        String sampleData = "{\"type\":\"form\",\"definition\":\"super\",\"formName\":\"FormName\"}";
        ObjectMapper mapper = new ObjectMapper();
        Definition definition = mapper.readValue(sampleData, Definition.class);
        System.out.println(definition);
    }
}

运行示例主应用程序将引发异常：

Running the sample main app will throw an exception:

Exception in thread "main" com.fasterxml.jackson.databind.JsonMappingException: Can not instantiate value of type [simple type, class jp.co.worksap.model.Definition] from String value ('super'); no single-String constructor/factory method (through reference chain: jp.co.worksap.model.FormDefinition["definition"])

似乎使用 AsPropertyTypeDeserializer 反序列化 FormDefinition的定义字段类而不是带注释的反序列化器 DefinitionDeserializer 。

which seems using AsPropertyTypeDeserializer to deserialize the definition field of FormDefinition class instead of the annotated deserializer DefinitionDeserializer.

我认为这里棘手的部分是我想使用自定义反序列化器的字段也是 Definition 的类型，它使用 @JsonTypeInfo 来解决多态问题。

I think the tricky part here is that the field I want to use custom deserializer is also type of Definition which using @JsonTypeInfo to solve the polymorphic problems.

有没有办法一起使用它们？谢谢。

Is there any way to use them together? Thanks.

推荐答案

杰克逊在选择使用哪个解串器之前处理 @JsonTypeInfo ，可能是因为反序列化器的选择通常取决于类型。但是，您可以在每个字段的基础上轻松禁用此功能，方法与指定自定义反序列化器相同 - 通过直接注释字段：

Jackson processes @JsonTypeInfo before choosing which Deserializer to use, probably because the choice of Deserializer could depend generally on the type. However, you can easily disable this on a per-field basis the same way you specify custom Deserializer - by annotating the field directly:

@JsonDeserialize(using = DefinitionDeserializer.class)
@JsonTypeInfo(use = JsonTypeInfo.Id.NONE)
private Definition definition;

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