Java deepclone an object without some properties

Question

I have following classes

class A {
    private Long id
    private List<B> listB;
    private C c;
    ...
}

class B {
    private Long id
    private A a;
    private List<D> listD;
    ...
}

class C {
    private Long id
    private A a;
    ...
}

class D {
    private Long id
    private B b;
    ...
}

I need a copy of A, include all of it's properties except all id column.

I have 2 solutions:
1. Clone each object and set all of the ids null;
2. Make a constructor like this:

public A (A a){
    //copy all properties except id
    this.xxx = a.xxx;
    ...
}

But i need write so much code for this function, any one has some better method to implement this function?
Thanks a lot.

Answer 1

When you are saying Deep cloning of the object particularly the one of type Class A where you have an instance variable of a container type, you have below two widely known ways:

1) You Serialize and Deserialize the object.

2) You traverse through each method and call clone explicitely.

For first implementation, you may mark the id fields as transient and that should solve your purpose.

For second approach, you may override the clone method in each class where you set the id field as 0/-1) and call super.clone()

Answer 2

You can use Mapstruct , it's a powerful mapping library where you can configure all the fields exclusions for your specific class or nested class, without having to write all the getters/setters manually. I personally use it for deep cloning jpa entities excluding ids or auditable fields. Ex:

@Mapping(target="id",ignore=true")
EntityA cloneEntityAWithoutId(EntityA origin);

Mapstruct will generate for you the implementations using getters and setters of the EntityA, excluding the id field. Obviously is a lot configurable, see the documentation I shared above.