How to run code after constructor in a Lombok builder

Question

I have a class that I want to use Lombok.Builder and I need pre-process of some parameters. Something like this:

@Builder
public class Foo {
   public String val         


        

Answer 1

I just stumbled upon the same issue. But additionally, I wanted to add an method buildOptional() to the builder to not repeat Optional.of(Foo) each time I need it. This did not work with the approach posted before because the chained methods return FooInternalBuilder objects; and putting buildOptional() into FooInternalBuilder would miss the init() method execution in Builder...

Also, I personally did not like the presence of 2 builder classes.

Here is what I did instead:

@Builder(buildMethodName = "buildInternal")
@ToString
public class Foo {
    public String val1;
    public int val2;
    @Singular  public List listValues;

    public void init(){
        // do some checks with the values.
    }    

    /** Add some functionality to the generated builder class */
    public static class FooBuilder {
        public Optional buildOptional() {
            return Optional.of(this.build());
        }

        public Foo build() {
            Foo foo = this.buildInternal();
            foo.init();
            return foo;
        }
    }
}

You can do a quick test with this main method:

public static void main(String[] args) {
    Foo foo = Foo.builder().val1("String").val2(14)
            .listValue("1").listValue("2").build();
    System.out.println(foo);

    Optional fooOpt = Foo.builder().val1("String").val2(14)
            .listValue("1").listValue("2").buildOptional();
    System.out.println(fooOpt);
}

Doing so let's you add what I want:

• Add an init() method which is executed after each object construction automatically
• Adding new fields do not require additional work (as it would be for an individually written constructor)
• Possibility to add additional functionality (incl. the init() execution)
• Retain the complete standard functionality the @Builder annotation brings
• Don't expose an additional builder class

Even if you solved your problem before I like to share this as the solution. It is a bit shorter and adds a (for me) nice feature.