你还在 new 对象吗？Java8 通用 Builder 了解一

程序员经常会遇到灵魂拷问：你有对象吗？
没有，但我可以 new 一个！

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 Listhobby;
  private String birthday;
  private String address;
  private String mobile;
  private String email;
  private String hairColor;
  private Mapgift;
  // 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);
    myGirlFriend.setHips(33);
    myGirlFriend.setBirthday("2001-10-26");
    myGirlFriend.setAddress("上海浦东");
    myGirlFriend.setMobile("18688888888");
    myGirlFriend.setEmail("pretty-xiaomei@qq.com");
    myGirlFriend.setHairColor("浅棕色带点微卷");
    Listhobby = new ArrayList<>();
    hobby.add("逛街");
    hobby.add("购物");
    hobby.add("买东西");
    myGirlFriend.setHobby(hobby);
    Mapgift = new HashMap<>();
    gift.put("情人节礼物", "LBR 1912女王时代");
    gift.put("生日礼物", "迪奥烈焰蓝金");
    gift.put("纪念日礼物", "阿玛尼红管唇釉");
    myGirlFriend.setGift(gift);
    // 等等等等 ...
  }
}

GirlFriend{name='小美'
, age=18
, bust=33
, waist=23
, hips=33
, hobby=[逛街, 购物, 买东西]
, birthday='2001-10-26'
, address='上海浦东'
, mobile='18688888888'
, email='pretty-xiaomei@qq.com'
, hairColor='浅棕色带点微卷'
, gift={情人节礼物=LBR 1912女王时代, 生日礼物=迪奥烈焰蓝金, 纪念日礼物=阿玛尼红管唇釉}
}

GirlFriend 是很美，但写起来也太麻烦了吧。

说说缺点：实例化和设置属性分开，不好维护；变量名重复写。

莫慌，看法宝~

这里不再介绍其他 Builder 实现方式，直接祭出最实用的通用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<T> {
  private final Supplierinstantiator;
  private List<consumer> modifiers = new ArrayList<>();
  public Builder(Supplierinstantiator){
    this.instantiator = instantiator;
  }
  public staticBuilderof(Supplierinstantiator){
    return new Builder<>(instantiator);
  }
  publicBuilderwith(Consumer1consumer, P1 p1){
    Consumerc = instance -> consumer.accept(instance, p1);
    modifiers.add(c);
    return this;
  }
  publicBuilderwith(Consumer2consumer, P1 p1, P2 p2){
    Consumerc = instance -> consumer.accept(instance, p1, p2);
    modifiers.add(c);
    return this;
  }
  publicBuilderwith(Consumer3consumer, P1 p1, P2 p2, P3 p3){
    Consumerc = 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。

快用你的 Builder 建个对象吧~

来自：rrd.me/gtQTp