How to use Lombok @Builder annotation on Methods

Question

I want to have an easy way to construct test data and have found the Builder pattern to be a good fit as described here. However to reduce boilerplate codes in the component tests, even more, I have found @Builder from Project Lombok to be a nice candidate to try. However, I can't find any documentation or online examples on how to use it on a method. I want to use @Builder on some sort of factory method since I can't make any changes to the implementation.

Can someone give an example on how to actually use @Builder on a method?

Answer 1

This is how you use @Builder.

//Employee.Java import lombok.Builder; import lombok.ToString;  @Builder @ToString public class Employee {    private final String empName;    private final int salary; }  //   Main.java  public class Main {  public static void main(String[] args) {     Employee emp = Employee.builder().empName("Deendaya").salary(100).build();     System.out.println(emp);   } } 

Answer 2

Using @Builder on method to create a Dog and Cat instance.

In this example @Value creates a final immutable value object with accessor methods (getters), an all args constructor, equals(), hashCode() and toString().

import static org.junit.Assert.*; import lombok.Builder; import lombok.Value;  import org.junit.Test;  @SuppressWarnings("javadoc") public class ImmutableAnimals {      @Builder(builderMethodName = "dogBuilder")     public static Dog newDog(String color, String barkSound) {         return new Dog(color, barkSound);     }      @Builder(builderMethodName = "catBuilder")     public static Cat newCat(String color, String meowSound) {         return new Cat(color, meowSound);     }      public static interface Animal {         String getColor();     }      @Value     public static class Cat implements Animal {         String color;         String meowSound;     }      @Value     public static class Dog implements Animal {         String color;         String barkSound;     }      @Test     public void testDog() {         final String expectedBarkSound = "woof";         final String expectedColor = "brown";          final Dog dog = ImmutableAnimals.dogBuilder()             .barkSound(expectedBarkSound)             .color(expectedColor)             .build();          assertEquals(expectedBarkSound, dog.getBarkSound());         assertEquals(expectedColor, dog.getColor());     }      @Test     public void testCat() {         final String expectedMeowSound = "purr";         final String expectedColor = "white";          final Cat cat = ImmutableAnimals.catBuilder()             .meowSound(expectedMeowSound)             .color(expectedColor)             .build();          assertEquals(expectedMeowSound, cat.getMeowSound());         assertEquals(expectedColor, cat.getColor());     } } 

Here's another example with the same domain classes but using mutable values. However, as always favor immutability whenever possible.

import static org.junit.Assert.*; import lombok.Builder; import lombok.Data;  import org.junit.Test;  @SuppressWarnings("javadoc") public class MutableAnimals {      @Builder(builderMethodName = "dogBuilder")     public static Dog newDog(String color, String barkSound) {         final Dog dog = new Dog();         dog.setBarkSound(barkSound);         dog.setColor(color);         return dog;     }      @Builder(builderMethodName = "catBuilder")     public static Cat newCat(String color, String meowSound) {         final Cat cat = new Cat();         cat.setMeowSound(meowSound);         cat.setColor(color);         return cat;     }      public static interface Animal {         String getColor();     }      @Data     public static class Cat implements Animal {         String color;         String meowSound;     }      @Data     public static class Dog implements Animal {         String color;         String barkSound;     }      @Test     public void testDog() {         final String expectedBarkSound = "woof";         final String expectedColor = "brown";          final Dog dog = MutableAnimals.dogBuilder()             .barkSound(expectedBarkSound)             .color(expectedColor)             .build();          assertEquals(expectedBarkSound, dog.getBarkSound());         assertEquals(expectedColor, dog.getColor());     }      @Test     public void testCat() {         final String expectedMeowSound = "purr";         final String expectedColor = "white";          final Cat cat = MutableAnimals.catBuilder()             .meowSound(expectedMeowSound)             .color(expectedColor)             .build();          assertEquals(expectedMeowSound, cat.getMeowSound());         assertEquals(expectedColor, cat.getColor());     } }