How to lazy instantiate attributes with JPA/Hibernate?

Question

I have been working with custom attribute types, and JPA's Attribute Converter.

For an example @Entity class like so:

@Entity
public class ExampleEntity {

    private CustomAttribute customAttribute = new CustomAttribute();

    public CustomAttribute getCustomAttribute() {
        if(this.customAttribute == null){
            this.customAttribute = new CustomAttribute();
        }
        return this.customAttribute;
    }
}

My CustomAttribute has some attributes of itself, and I do not want it to be null (ever). I had to choose between two alternatives, and both of those were examplified simultaneously:

1. Instantiate the object on attribute declaration (like I did on the example for the field).
2. Instantiate a new object for that attribute in case of a true null checking on a getter.

Since my @Entity on production application has more than 10 attributes, it would be too verbose to apply any of those alternatives on all fields/getters.

Question: Is there any way to instantiate the CustomAttribute object on null field access?

I could not find any answer for this specific question on my research online, so any insight would be appreciated.

EDIT: My question is not about lazy instantiating of fields on relationship mappings, it is about instantiating custom attribute objects on access.

Answer 1

Bit of a hacky solution, you may prefer it plain java approach you yourself suggested:

I created a class called MyClass, which has following consturctor:

@Data // Lombok annotation
public class ExampleEntity {

    @NotNullGetter
    private CustomAttribute customAttribute;

    public ExampleEntity() {

        Class<?> cls = this.getClass();

        for(Field field: cls.getDeclaredFields()) {
            if(field.isAnnotationPresent(NotNullGetter.class)) {
                Class clazz = field.getType();
                try {
                    for(Method method: cls.getDeclaredMethods()) {

                        if(method.getName().startsWith("set") && method.getName().toLowerCase().endsWith(field.getName().toLowerCase())) {
                            // This will create not null object.
                            method.invoke(this, field.getType().newInstance());
                        }
                    }
                } catch (InstantiationException e) {
                    e.printStackTrace();
                } catch (IllegalAccessException e) {
                    e.printStackTrace();
                } catch (InvocationTargetException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}

And my @NotNullGetter annotation

   import java.lang.annotation.*;

    @Retention(RetentionPolicy.RUNTIME)
    @Target(ElementType.FIELD)
    @Documented
    public @interface NotNullGetter {
    }