'@ RequiredArgsConstructor'和'MismatchedInputException：无法构造实例'

Question

我有多个看起来像这样的DTO对象：

@Getter
@RequiredArgsConstructor
public class SomeDTO {
  private final String someProperty;
}

这些DTO对象被各种RestController方法接受：

@RestController
public void InvitationController {

  @PostMapping
  public String create(@RequestBody InvitationCreationDTO invitationCreationDTO) {
    // some logic
    return "ok";
  }

}

Jackson does not have an issue deserializing json to these classes, except for the following one:

```java
@Getter
@RequiredArgsConstructor
public class InvitationCreationDTO {
  private final String emailAddress;
}

[当Jackson尝试反序列化以下JSON时：

{ "emailAddress" : "[email protected]" }

抛出此错误：

Caused by: com.fasterxml.jackson.databind.exc.MismatchedInputException: Cannot construct instance of `my.package.InvitationCreationDTO` (although at least one Creator exists): cannot deserialize from Object value (no delegate- or property-based Creator)
 at [Source: (PushbackInputStream); line: 1, column: 2]
    at com.fasterxml.jackson.databind.exc.MismatchedInputException.from(MismatchedInputException.java:63) ~[jackson-databind-2.10.2.jar:2.10.2]
    at com.fasterxml.jackson.databind.DeserializationContext.reportInputMismatch(DeserializationContext.java:1429) ~[jackson-databind-2.10.2.jar:2.10.2]
    at com.fasterxml.jackson.databind.DeserializationContext.handleMissingInstantiator(DeserializationContext.java:1059) ~[jackson-databind-2.10.2.jar:2.10.2]
    at com.fasterxml.jackson.databind.deser.BeanDeserializerBase.deserializeFromObjectUsingNonDefault(BeanDeserializerBase.java:1297) ~[jackson-databind-2.10.2.jar:2.10.2]
    at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserializeFromObject(BeanDeserializer.java:326) ~[jackson-databind-2.10.2.jar:2.10.2]
    at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:159) ~[jackson-databind-2.10.2.jar:2.10.2]
    at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:4202) ~[jackson-databind-2.10.2.jar:2.10.2]
    at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:3258) ~[jackson-databind-2.10.2.jar:2.10.2]
    at org.springframework.http.converter.json.AbstractJackson2HttpMessageConverter.readJavaType(AbstractJackson2HttpMessageConverter.java:239) ~[spring-web-5.2.3.RELEASE.jar:5.2.3.RELEASE]
    ... 86 common frames omitted

但是，当我删除@RequiredArgsConstructor并自己创建一个时：

@Getter
public class InvitationCreationDTO {
  private final String emailAddress;

  @JsonCreator
  public InvitationCreationDTO(String emailAddress) {
    this.emailAddress = emailAddress;
  }
}

为什么这个类需要这个，但是我的其他DTO类（具有相同的格式）却不需要？

Answer 1

尝试将@NoArgsConstructor添加到您的InvitationCreationDTO类中>

@Getter
@NoArgsConstructor
@RequiredArgsConstructor
public class InvitationCreationDTO {
  private final String emailAddress;
}