Builder一个对象

一般新建对象我们都是直接new一下

public class GirlFriend {
private String name;
private int age;
// 省略 getter & setter ...
public static void main(String[] args) {
GirlFriend myGirlFriend = new GirlFriend();
myGirlFriend.setName("小美");
myGirlFriend.setAge(18);
}
}
没问题，老铁！但如果对象的属性太多，咋办？

public class GirlFriend {
private String name;
private int age;
private int bust;
private int waist;
private int hips;
private List hobby;
// 等等等等 ...
// 省略 getter & setter ...
public static void main(String[] args) {
GirlFriend myGirlFriend = new GirlFriend();
myGirlFriend.setName("小美");
myGirlFriend.setAge(18);
myGirlFriend.setBust(33);
myGirlFriend.setWaist(23);
// 等等等等 ...
}
}

而Java8通用Builder适用于所有类，不需要改造原来类，不需要 lombok 插件支持。

先看看使用姿势：

public class GirlFriend {
// 省略属性 ...
// 省略 getter & setter ...

// 为了演示方便，加几个聚合方法
public void addHobby(String hobby) {
    this.hobby = Optional.ofNullable(this.hobby).orElse(new ArrayList<>());
    this.hobby.add(hobby);
}
public void addGift(String day, String gift) {
    this.gift = Optional.ofNullable(this.gift).orElse(new HashMap<>());
    this.gift.put(day, gift);
}
public void setVitalStatistics(int bust, int waist, int hips) {
    this.bust = bust;
    this.waist = waist;
    this.hips = hips;
}
public static void main(String[] args) {
    GirlFriend myGirlFriend = Builder.of(GirlFriend::new)
            .with(GirlFriend::setName, "小美")
            .with(GirlFriend::setAge, 18)
            .with(GirlFriend::setVitalStatistics, 33, 23, 33)
            .with(GirlFriend::setBirthday, "2001-10-26")
            .with(GirlFriend::setAddress, "上海浦东")
            .with(GirlFriend::setMobile, "18688888888")
            .with(GirlFriend::setEmail, "pretty-xiaomei@qq.com")
            .with(GirlFriend::setHairColor, "浅棕色带点微卷")
            .with(GirlFriend::addHobby, "逛街")
            .with(GirlFriend::addHobby, "购物")
            .with(GirlFriend::addHobby, "买东西")
            .with(GirlFriend::addGift, "情人节礼物", "LBR 1912女王时代")
            .with(GirlFriend::addGift, "生日礼物", "迪奥烈焰蓝金")
            .with(GirlFriend::addGift, "纪念日礼物", "阿玛尼红管唇釉")
            // 等等等等 ...
            .build();
}

}
看到了吗！实例化和属性设置在同一条语句执行，链式操作，一路点点点，清爽！

Talk is cheap, show me the code：

/**

• 通用的 Builder 模式构建器
• @author: CipherCui
• @since 2019/8/29
  /
  public class Builder {
  private final Supplier instantiator;
  private List<Consumer> modifiers = new ArrayList<>();
  public Builder(Supplier instantiator) {
  this.instantiator = instantiator;
  }
  public static Builder of(Supplier instantiator) {
  return new Builder<>(instantiator);
  }
  public Builder with(Consumer1<T, P1> consumer, P1 p1) {
  Consumer c = instance -> consumer.accept(instance, p1);
  modifiers.add(c);
  return this;
  }
  public <P1, P2> Builder with(Consumer2<T, P1, P2> consumer, P1 p1, P2 p2) {
  Consumer c = instance -> consumer.accept(instance, p1, p2);
  modifiers.add(c);
  return this;
  }
  public <P1, P2, P3> Builder with(Consumer3<T, P1, P2, P3> consumer, P1 p1, P2 p2, P3 p3) {
  Consumer c = instance -> consumer.accept(instance, p1, p2, p3);
  modifiers.add(c);
  return this;
  }
  public T build() {
  T value = instantiator.get();
  modifiers.forEach(modifier -> modifier.accept(value));
  modifiers.clear();
  return value;
  }
  /*
  • 1 参数 Consumer
    /
    @FunctionalInterface
    public interface Consumer1<T, P1> {
    void accept(T t, P1 p1);
    }
    /*
  • 2 参数 Consumer
    /
    @FunctionalInterface
    public interface Consumer2<T, P1, P2> {
    void accept(T t, P1 p1, P2 p2);
    }
    /*
  • 3 参数 Consumer
    */
    @FunctionalInterface
    public interface Consumer3<T, P1, P2, P3> {
    void accept(T t, P1 p1, P2 p2, P3 p3);
    }
    }
    这个示例最多支持三个参数的设置属性方法，也完全够用了。如果要扩展也很容易，依葫芦画瓢，添加多个参数的Consumer。

参考：http://www.ciphermagic.cn/java8-builder.html