Feature Proposal - Enhanced Null-Protection for Objects Created Outside of Builder Pattern

[Kirill Andreev]

Hello Lombok Community,

I hope this message finds you well. I've been exploring Lombok's capabilities, particularly the @Builder annotation, and I've identified a scenario where enhanced null-protection could greatly improve compatibility with external libraries, such as Gson.

Problem Statement:

While Lombok's @Builder annotation efficiently handles null-protection when using @Builder.Default, certain libraries, like Gson, create objects without utilizing builders. In such cases, the absence of a default/no-argument constructor poses challenges, as these libraries rely on this type of constructor for object instantiation.

Proposed Solution:

I suggest enhancing the @Builder functionality in Lombok to automatically generate a default/no-argument constructor. This constructor would initialize fields with their respective @Builder.Default values, ensuring consistent null-protection even when objects are created outside of the builder pattern.

[Mat Jaggard]

Hi Kirill,

@NoArgsConstructor  already does exactly that.

Thanks,

Mat.

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[Kirill Andreev]

Thanks Mat

You are partially correct - @NoArgConstructor will generate a constructor with no parameters.
However, "fields are initialized with 0 / false / null". It does not say it respects @Builder.Default values.

Here is the example:

@NoArgsConstructor
@Builder
public class Book {
@Builder.Default
public final String title = "Book";
@Builder.Default
public final String author = "Agatha christie";
}

The class is failed to compile. Here is the error:

java: constructor Book in class app.Book cannot be applied to given types;
  required: no arguments
  found:    java.lang.String,java.lang.String

  reason: actual and formal argument lists differ in length 

I am trying with 1.18.30

Let me know if I am missing something

[Mat Jaggard]

Got you. That's because by defining `@NoArgsConstructor` you're explicitly creating a constructor which `@Builder` will then use - so you have no parameters. You need to specify all 3 - `@NoArgsConstructor` `@AllArgsConstructor` and `@Builder`.

I forgot about that because I normally use `@SuperBuilder` which doesn't have this issue. It always creates a new constructor which just takes the builder object.

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[Kirill Andreev]

Thank you, Mat!

I appreciate your help, and the solution works perfectly for my needs. I believe this valuable information could benefit others in the Lombok community. Is it possible to include this in the documentation? I believe a shot note for Builder annotation would be sufficient. 

Thanks again,

[Mat Jaggard]

I've created a PR to attempt to explain this. https://github.com/projectlombok/lombok/pull/3560

(Also, note to the maintainers of Lombok, I have another outstanding PR https://github.com/projectlombok/lombok/pull/3548 )

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