InvalidDefinitionException: "Argument #0 of constructor has no property name"

[NadChel]

I have trouble deserializing a JSON. My DTO class has a special private constructor for that. I annotated it with @JsonCreator

@Getter
public class QuestionCommentResponseDto {
    private final Long id;
    private final Long questionId;
    private final LocalDateTime createdDate;
    private final LocalDateTime modifiedDate;
    private final String text;
    @Setter
    private AccountResponseDto owner;

    public QuestionCommentResponseDto(Long id, Long questionId, LocalDateTime createdDate,
                                      LocalDateTime modifiedDate, String text) {
        this.id = id;
        this.questionId = questionId;
        this.createdDate = createdDate;
        this.modifiedDate = modifiedDate;
        this.text = text;
    }
    @JsonCreator
    private QuestionCommentResponseDto(Long id, Long questionId, LocalDateTime createdDate,
                                      LocalDateTime modifiedDate, String text,
                                      AccountResponseDto owner) {
        this(id, questionId, createdDate, modifiedDate, text);
        this.owner = owner;
    }
// equals() and hashcode()
}

// the associated DTO
@AllArgsConstructor
@NoArgsConstructor
@Getter
@Setter
public class AccountResponseDto {

    private Long id;
    private String username;
// equals() and hashcode()

For some reason, Jackson can't use the designated constructor. The error message is obscure

com.fasterxml.jackson.databind.exc.InvalidDefinitionException: Invalid type definition for type `stack.overflow.model.dto.response.QuestionCommentResponseDto`: Argument #0 of constructor [constructor for `stack.overflow.model.dto.response.QuestionCommentResponseDto` (6 args), annotations: {interface com.fasterxml.jackson.annotation.JsonCreator=@com.fasterxml.jackson.annotation.JsonCreator(mode=DEFAULT)} has no property name (and is not Injectable): can not use as property-based Creator
 at [Source: (String)"{"data":{"id":1,"questionId":1,"createdDate":"2023-06-03T20:16:57.238883","modifiedDate":"2023-06-03T20:16:57.238883","text":"text","owner":{"id":1,"username":"mickey_m"}}}"; line: 1, column: 1]

What does it mean? What is "argument #0"? "id"? How is it problematic? It perfectly matches the field in name and type so I expect Jackson to be smart enough to map them together. And most importantly, how do I fix this problem?

[cowtowncoder]

It means that unless you have registered module jackson-module-parameter-names (see https://github.com/FasterXML/jackson-modules-java8/), names of Constructor arguments are not detected. This separation is due to historical reasons as functionality only became available on Java 8 and Jackson used to work on earlier JDKs as well.
Without this module, you would need to add @JsonProperty next to constructor argument names: #0 refers to the first one (arguments are 0-indexed).

So: you want to make sure to include jackson-module-parameter-names as per README at https://github.com/FasterXML/jackson-modules-java8/ (need a Maven / Gradle dependency to get it; then use registerModule or addModule).

Alternatively, since you are using a framework (Lombok?), it might have means to generate annotations to indicate names, without you having to do it beyond configuration (or a single Lombok-specific annotation).

Hope this helps.

[NadChel]

It does. Thanks a lot 🙏