Builder

While having a builder alongside Kotlin constructors might seem redundant, it can be useful when using models in Java and especially with backend development. Therefore, the Builder annotation was added.

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Usage

Make sure you’ve setup the plugin first

Then use the annotation on your data class and add companion object as the following

@Serializable
@JsExport
@Builder
data class User(val id: String, var name: String? = null, var age: Int? = null) {
    /**
     * Converts the object into a json object
     */
    fun json(): String {
        return toJson()
    }

    /**
     * Converts the object into a formatted json object
     */
    fun jsonPretty(): String {
        return toJsonPretty()
    }

    companion object {
        @JvmStatic
        fun builder(id: String): UserBuilder {
            return UserBuilder(id)
        }
    }
}

Nullability

For the builder annotation to be useful make sure to have most of the fields as nullable, otherwise you gonna have to manually add the the none nullable fields to the companion builder function just like id in the example above.

Now you can use the builder

public class Test {
    public static void main(String[] args) {
        User user = User.builder("1")
                .name("foo")
                .age(20)
                .build();

        user.json();
    }
}