你还在 new 对象吗？Java8 通用 Builder 了解一下？

来源：cipher

ciphermagic.cn/java8-builder.html

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 static Builderof(Supplierinstantiator) { return new Builder<>(instantiator); } public Builderwith(Consumer1consumer, P1 p1) { Consumerc = instance -> consumer.accept(instance, p1); modifiers.add(c); return this; } public Builderwith(Consumer2consumer, P1 p1, P2 p2) { Consumerc = instance -> consumer.accept(instance, p1, p2); modifiers.add(c); return this; } public Builderwith(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~