如何学习杰克逊铸造抽象类的继承者? [英] How to learn Jackson to cast inheritors of abstract class?

问题描述

我有一堂课

@EqualsAndHashCode(callSuper = true)
@Data
public class AppealTemplateDto extends AbstractDto {

    private List<AbstractFieldDto> fields;
}

此类包含 AbstractFieldDto 继承者的列表，例如:

This class contains list of AbstractFieldDto inheritors, e.g.:

@EqualsAndHashCode(callSuper = true)
@Data
@NoArgsConstructor
public class InputFieldDto extends AbstractFieldDto {

    private String fieldType = FieldType.INPUT.name();
    private String text;
}

总共有近6-7个继承者，&AbstractTemplateDto可以包含任何一组.

Totally, there are near 6-7 inheritors, & AbstractTemplateDto may contain any set of them.

控制器:

@PostMapping
public ResponseEntity<AppealTemplateDto> create(@RequestBody AppealTemplateDto dto) {
    return ResponseEntity.ok(service.save(dto));
}

当Jackson尝试解析 AppealTemplateDto 时，它崩溃并发生异常:

When Jackson trying to parse AppealTemplateDto, it crashes with exception:

起因:com.fasterxml.jackson.databind.exc.InvalidDefinitionException:无法构造的实例 ru.appeal.template.dto.field.AbstractFieldDto (不存在创建者，例如默认构造):抽象类型需要映射到具体类型，具有自定义反序列化器，或包含其他类型信息

Caused by: com.fasterxml.jackson.databind.exc.InvalidDefinitionException: Cannot construct instance of ru.appeal.template.dto.field.AbstractFieldDto (no Creators, like default construct, exist): abstract types either need to be mapped to concrete types, have custom deserializer, or contain additional type information

据我了解，Jackson无法定义如何将传入的 AbstractFieldDto强制转换为.请给我建议，该怎么办?

As I understand, Jackson can't define, how to cast incoming AbstractFieldDto. Please, advice me, what to do?

推荐答案

您需要的注释是:

@JsonTypeInfo
@JsonSubType

@JsonTypeName

一些解释:如果您有很多抽象类型的实现，Jackson不能猜测您的json是哪种类型，则需要在json中添加类型名称，例如作为新属性(这是一种策略)):

Some explanation: if you have many implementation of your abstract type, Jackson can't guess which type is your json, you need to add a type name in json, for example as a new property (this is one of the strategies):

//tell to jackson where to find the type name
@JsonTypeInfo(   use = JsonTypeInfo.Id.NAME, include = As.PROPERTY, property = "type")
// tell to jackson the implementations to scan
@JsonSubTypes({
    @JsonSubTypes.Type(value = InputFieldDto.class, name = "input")
    //, ...
})
public class AbstractFieldDto {
}

//tell to jackson what is the type name in json
@JsonTypeName("input")
public class InputFieldDto extends AbstractFieldDto {

    private String fieldType = FieldType.INPUT.name();
    private String text;
}

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