Lombokの@Builder(toBuilder = true)で、オブジェクトの複製を作成する

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前回の記事の続きで。

@Builder(toBuilder = true)とすると、オブジェクトからBuilderを生成できます。

どういうときに使えるかというと、オブジェクトの複製を作成して、一部のプロパティのみ変えたいといった場合です。

package com.example.lombok;

import lombok.Builder;
import lombok.ToString;

public class BuilderExample {

    public static void main(String[] args) {

        Customer customer1 = new Customer("Taro", "Urashima", "ura@exmple.com", "111-111-1111");

        System.out.println(customer1);

        Customer customer2 = customer1.toBuilder()
                .lastName("Yamada")
                .build();

        System.out.println(customer2);
    }
}

@Builder(toBuilder = true)
@ToString
class Customer {

    private String firstName;

    private String lastName;

    private String mailAddress;

    private String telephone;
}

実行結果は下記の通りです。lastNameだけが異なるオブジェクトが生成されます。

Customer(firstName=Taro, lastName=Urashima, mailAddress=ura@exmple.com, telephone=111-111-1111)
Customer(firstName=Taro, lastName=Yamada, mailAddress=ura@exmple.com, telephone=111-111-1111)

Lombokで生成されるのは、下記のようなコードになります。(delombokで確認)

class Customer {
    private String firstName;
    private String lastName;
    private String mailAddress;
    private String telephone;

    @java.lang.SuppressWarnings("all")
    @javax.annotation.Generated("lombok")
    Customer(final String firstName, final String lastName, final String mailAddress, final String telephone) {
        this.firstName = firstName;
        this.lastName = lastName;
        this.mailAddress = mailAddress;
        this.telephone = telephone;
    }


    @java.lang.SuppressWarnings("all")
    @javax.annotation.Generated("lombok")
    public static class CustomerBuilder {
        @java.lang.SuppressWarnings("all")
        @javax.annotation.Generated("lombok")
        private String firstName;
        @java.lang.SuppressWarnings("all")
        @javax.annotation.Generated("lombok")
        private String lastName;
        @java.lang.SuppressWarnings("all")
        @javax.annotation.Generated("lombok")
        private String mailAddress;
        @java.lang.SuppressWarnings("all")
        @javax.annotation.Generated("lombok")
        private String telephone;

        @java.lang.SuppressWarnings("all")
        @javax.annotation.Generated("lombok")
        CustomerBuilder() {
        }

        @java.lang.SuppressWarnings("all")
        @javax.annotation.Generated("lombok")
        public CustomerBuilder firstName(final String firstName) {
            this.firstName = firstName;
            return this;
        }

        @java.lang.SuppressWarnings("all")
        @javax.annotation.Generated("lombok")
        public CustomerBuilder lastName(final String lastName) {
            this.lastName = lastName;
            return this;
        }

        @java.lang.SuppressWarnings("all")
        @javax.annotation.Generated("lombok")
        public CustomerBuilder mailAddress(final String mailAddress) {
            this.mailAddress = mailAddress;
            return this;
        }

        @java.lang.SuppressWarnings("all")
        @javax.annotation.Generated("lombok")
        public CustomerBuilder telephone(final String telephone) {
            this.telephone = telephone;
            return this;
        }

        @java.lang.SuppressWarnings("all")
        @javax.annotation.Generated("lombok")
        public Customer build() {
            return new Customer(firstName, lastName, mailAddress, telephone);
        }

        @java.lang.Override
        @java.lang.SuppressWarnings("all")
        @javax.annotation.Generated("lombok")
        public java.lang.String toString() {
            return "Customer.CustomerBuilder(firstName=" + this.firstName + ", lastName=" + this.lastName + ", mailAddress=" + this.mailAddress + ", telephone=" + this.telephone + ")";
        }
    }

    @java.lang.SuppressWarnings("all")
    @javax.annotation.Generated("lombok")
    public static CustomerBuilder builder() {
        return new CustomerBuilder();
    }

    @java.lang.SuppressWarnings("all")
    @javax.annotation.Generated("lombok")
    public CustomerBuilder toBuilder() {
        return new CustomerBuilder().firstName(this.firstName).lastName(this.lastName).mailAddress(this.mailAddress).telephone(this.telephone);
    }

    @java.lang.Override
    @java.lang.SuppressWarnings("all")
    @javax.annotation.Generated("lombok")
    public java.lang.String toString() {
        return "Customer(firstName=" + this.firstName + ", lastName=" + this.lastName + ", mailAddress=" + this.mailAddress + ", telephone=" + this.telephone + ")";
    }
}