no-args constructor

[haileyKimDev]

Hi. I have a question regarding the case when there is no parameterless ("default") constructor.
In the context of the README content, " in which case module can force instantiation of values without using any constructor."

Does it still support the case where there is no parameterless ("default") constructor?
The reason why is that both JDK 11 and 14 required the presence of a no-args constructor.

[cowtowncoder]

I am guessing you are asking about specific module from jackson-modules-base?

https://github.com/FasterXML/jackson-modules-base/tree/2.16/no-ctor-deser

It only needs to be used if you cannot annotate other constructors with @JsonCreator for use.

Otherwise I am not quite sure what you are asking.

[haileyKimDev]

@cowtowncoder Thank you for your comment!
I am working on a project using Spring Boot version 2.7.9 and JDK 11.
When I execute the code to create a DTO class as follows, I encounter the following error.

Here is the dto class :

@Getter
@AllArgsConstructor
@Builder
public class CartCreateDto {

  private final Long productId;
  private final int count;

  public Cart toEntity(Long memberId) {
    return Cart.builder()
        .productId(getProductId())
        .memberId(memberId)
        .count(getCount())
        .build();
  }
}

The above class satisfies both conditions: it does not require a no-arguments ("default") constructor and it does not have an @JsonCreator annotated constructor or factory method. Therefore, I didn't think @NoArgsConstructor was necessary.

However, I'm encountering the following error.

com.fasterxml.jackson.databind.exc.InvalidDefinitionException: Cannot construct instance of cart.dto.CartCreateDto (no Creators, like default constructor, exist): cannot deserialize from Object value (no delegate- or property-based Creator)

Am I misunderstanding something?

[mohanaraosv]

Lombok and Jackson marriage made in heaven.

Use the following annotation when we use builder : https://projectlombok.org/features/experimental/Jacksonized

[haileyKimDev]

@mohanaraosv
oh Thank you so much
it works!

[cowtowncoder]

@NoArgsConstructor is not a Jackson annotation so Jackson has no idea of what it should mean; rather, framework that provides it (Lombok?) would know, so question is more about Lombok usage. It sounds like @mohanaraosv was able to help here fortunately.

[haileyKimDev]

@cowtowncoder
Thank you for your feedback.
I thought that the no args constructor was related to the Jackson library.
because the Jackson library is used to deserialize JSON data into Java objects so I understood that the Jackson library requires a default constructor (@no args constructor) in the corresponding object for deserialization.
I'll look into Lombok more. Thank you for your response!

[cowtowncoder]

Jackson may require no-args constructor in some cases, yes. I was just confused by reference to:

"...in which case module can force instantiation of values without using any constructor."

which I don't think is something Jackson READMEs say.

Anyway, one is not needed in all cases; there does have to be some means of constructing an instance however.

[haileyKimDev]

@cowtowncoder

Hello,
I finally figured out the reason why I was getting the "no args constructor" error in the terminal. It turns out that I had selected Intellij as the build and run configuration, which caused the Gradle plugins to not work properly.

Once I switched the build and run configuration to Gradle, the error no longer occurred.

Thank you for your help and comments :)