Required arguments with a Lombok @Builder

Question

If I add @Builder to a class. The builder method is created.

Person.builder().name(\"john\").surname(\"Smith\").build();

I have a requirem

Answer 1

This is my solution for the problem

import lombok.Builder;
import lombok.Data;
import lombok.NonNull;

@Data
@Builder(builderMethodName = "privateBuilder")
public class Person {
    @NonNull
    private String name;
    @NonNull
    private String surname;
    private int age;//optional

public static Url safeBuilder() {
    return new Builder();
}

interface Url {
    Surname name(String name);
}

interface Surname {
    Build surname(String surname);
}

interface Build {
    Build age(int age);
    Person build();
}

public static class Builder implements Url, Surname, Build {
    PersonBuilder pb = Person.privateBuilder();

    @Override
    public Surname name(String name) {
        pb.name(name);
        return this;
    }

    @Override
    public Build surname(String surname) {
        pb.surname(surname);
        return this;

    }

    @Override
    public Build age(int age) {
        pb.age(age);
        return this;
    }

    @Override
    public Person build() {
        return pb.build();
    }
    }
}

inspired by this blog post:

https://blog.jayway.com/2012/02/07/builder-pattern-with-a-twist/

Answer 2

The simpliest solution is to add a @lombok.NonNull to all mandatory values. The Builder will fail to build the object when mandatory fields are not set.

Here's a JUnit test to demonstrate the behavior of all combinations of final and @NonNull:

import static org.junit.Assert.fail;

import org.junit.Test;

import lombok.Builder;
import lombok.ToString;

public class BuilderTests {
    @Test
    public void allGiven() {
        System.err.println(Foo.builder()
            .nonFinalNull("has_value")
            .nonFinalNonNull("has_value")
            .finalNull("has_value")
            .finalNonNull("has_value")
            .build());
    }

    @Test
    public void noneGiven() {
        try {
            System.err.println(Foo.builder()
                .build()
                .toString());
            fail();
        } catch (NullPointerException e) {
            // expected
        }
    }

    @Test
    public void nonFinalNullOmitted() {
        System.err.println(Foo.builder()
            .nonFinalNonNull("has_value")
            .finalNull("has_value")
            .finalNonNull("has_value")
            .build());
    }

    @Test
    public void nonFinalNonNullOmitted() {
        try {
            System.err.println(Foo.builder()
                .nonFinalNull("has_value")
                .finalNull("has_value")
                .finalNonNull("has_value")
                .build());
            fail();
        } catch (NullPointerException e) {
            // expected
        }
    }

    @Test
    public void finalNullOmitted() {
        System.err.println(Foo.builder()
            .nonFinalNull("has_value")
            .nonFinalNonNull("has_value")
            .finalNonNull("has_value")
            .build());
    }

    @Test
    public void finalNonNullOmitted() {
        try {
            System.err.println(Foo.builder()
                .nonFinalNull("has_value")
                .nonFinalNonNull("has_value")
                .finalNull("has_value")
                .build());
            fail();
        } catch (NullPointerException e) {
            // expected
        }
    }

    @Builder
    @ToString
    private static class Foo {
        private String nonFinalNull;

        @lombok.NonNull
        private String nonFinalNonNull;

        private final String finalNull;

        @lombok.NonNull
        private final String finalNonNull;
    }
}

Answer 3

If you need this functionality, you can customize the builder class by yourself and you can still add @Builder Annotation.

@Builder
public class Person {

    public static class PersonBuilder {
        private String name;

        private PersonBuilder() {
        }

        public PersonBuilder(final String name) {
            this.name = name;
        }
    }

    private static PersonBuilder builder() {
        return null; // or we can throw exception.
    }

    public static PersonBuilder builder(final String name) {
        return new PersonBuilder(clientId);
    }
}