设计模式之建造者模式

概念

建造者模式（Builder），将一个复杂对象的构建与它的表示分离，使得同样的构建过程可以创建不同的表示

优点

• 与其他创作模式相比，对构建过程有更多的控制
• 支持逐步构造对象、推迟构造步骤或递归地运行步骤
• 可以构造需要子对象的复杂组合的对象，最终产品与对象的组成的部分以及对象的组装过程分离开来
• 单一职责原则，可以将复杂的构造代码与产品的业务逻辑隔分离开来

示例

创建英雄

public final class Hero {
    private final Profession profession;
    private final String name;
    private final HairType hairType;
    private final HairColor hairColor;
    private final Armor armor;
    private final Weapon weapon;

    private Hero(Builder builder) {
        this.profession = builder.profession;
        this.name = builder.name;
        this.hairColor = builder.hairColor;
        this.hairType = builder.hairType;
        this.weapon = builder.weapon;
        this.armor = builder.armor;
    }
}

  public static class Builder {
    private final Profession profession;
    private final String name;
    private HairType hairType;
    private HairColor hairColor;
    private Armor armor;
    private Weapon weapon;

    public Builder(Profession profession, String name) {
        if (profession == null || name == null) {
            throw new IllegalArgumentException("profession and name can not be null");
        }
        this.profession = profession;
        this.name = name;
    }

    public Builder withHairType(HairType hairType) {
        this.hairType = hairType;
        return this;
    }

    public Builder withHairColor(HairColor hairColor) {
        this.hairColor = hairColor;
        return this;
    }

    public Builder withArmor(Armor armor) {
        this.armor = armor;
        return this;
    }

    public Builder withWeapon(Weapon weapon) {
        this.weapon = weapon;
        return this;
    }

    public Hero build() {
        return new Hero(this);
    }
}

  public static void main(String[] args) {

    var mage = new Hero.Builder(Profession.MAGE, "Riobard")
            .withHairColor(HairColor.BLACK)
            .withWeapon(Weapon.DAGGER)
            .build();
    LOGGER.info(mage.toString());

    var warrior = new Hero.Builder(Profession.WARRIOR, "Amberjill")
            .withHairColor(HairColor.BLOND)
            .withHairType(HairType.LONG_CURLY).withArmor(Armor.CHAIN_MAIL).withWeapon(Weapon.SWORD)
            .build();
    LOGGER.info(warrior.toString());

    var thief = new Hero.Builder(Profession.THIEF, "Desmond")
            .withHairType(HairType.BALD)
            .withWeapon(Weapon.BOW)
            .build();
    LOGGER.info(thief.toString());
}

16:28:06.058 [main] INFO com.iluwatar.builder.App -- This is a mage named Riobard with black hair and wielding a dagger.
16:28:06.060 [main] INFO com.iluwatar.builder.App -- This is a warrior named Amberjill with blond long curly hair wearing chain mail and wielding a sword.
16:28:06.060 [main] INFO com.iluwatar.builder.App -- This is a thief named Desmond with bald head and wielding a bow.

什么时候使用建造者模式

• 非常适合需要创建复杂对象的Java应用程序

• 创建复杂对象的算法应该独立于组成对象的各个部分及其组装方式

• 构造过程必须允许所构造的对象具有不同的表示形式

• 当一个产品需要大量的步骤来创建，并且这些步骤需要按特定的顺序执行时，它特别有用用

注意事项

• 由于需要创建多个新类，因此代码的总体复杂性可能会增加
• 由于创建多个构建器对象，可能会增加内存使用