Skip to content

Build an object from an existing one using lombok

Lets say I have a lombok annotated class like

@Builder
class Band {
   String name;
   String type;
}

I know I can do:

Band rollingStones = Band.builder().name("Rolling Stones").type("Rock Band").build();

Is there an easy way to create an object of Foo using the existing object as a template and changing one of it’s properties?

Something like:

Band nirvana = Band.builder(rollingStones).name("Nirvana");

I can’t find this in the lombok documentation.

Answer

You can use the toBuilder parameter to give your instances a toBuilder() method.

@Builder(toBuilder=true)
class Foo {
   int x;
   ...
}

Foo f0 = Foo.builder().build();
Foo f1 = f0.toBuilder().x(42).build();

From the documentation:

If using @Builder to generate builders to produce instances of your own class (this is always the case unless adding @Builder to a method that doesn’t return your own type), you can use @Builder(toBuilder = true) to also generate an instance method in your class called toBuilder(); it creates a new builder that starts out with all the values of this instance.

Disclaimer: I am a lombok developer.