Customize lombok super builder

Question

I have a parent abstract class "Parent" and child class "Child". I am using @SuperBuilder to generate builder APIs. Now, I want to perform some validations on the members of class "Parent" and "Child" as part of build. I couldn't find any solution to customize lombok super builder. As per lombok doc, it seems to be possible. Can someone please shed some light?

@SuperBuilder
public abstract class Parent {
    int x;
    int y;
    int z;
    int a;
}

@SuperBuilder
public abstract class Child extends Parent {
    int b;
    int c;
    int d;

    // I want something like
    public static class ChildBuilder {

       public Child build() {
           Child child = // Get child somehow;
           validate(child);
       }
    }
}

Answer 1

The generated code for @SuperBuilder is complex and loaded with type parameters. Therefore, it is advisable to delombok your class and use the output as a reference.

You can do this with this command:

java -jar path/to/lombok.jar delombok -p path/to/src/main/java/Child.java

The output will show what code lombok generates. I assume the Child class is not abstract (I think you have a typo in your questions). You want to customize the build() method, so you are interested in the ChildBuilderImpl, because this class contains that method. You can copy the class header to your source file and add your custom build() method:

private static final class ChildBuilderImpl extends Child.ChildBuilder<Child, Child.ChildBuilderImpl> {
    @java.lang.Override
    public Child build() {
        // Do validation here, e.g.:
        if (((Child.ChildBuilder<?, ?>)this).b == 0)
            throw new IllegalArgumentException("b must not be 0");
        return new Child(this);
    }
}

Remark: I would prefer performing the validation in the constructor, because otherwise you could programmatically invoke the constructor without the values getting validated. However, customizing the @SuperBuilder constructor is not possible at the moment; it will be possible with the next lombok release. I'll update this question when it is released.

Update: You can customize the constructor since Lombok v1.18.16.