程序員經常會遇到靈魂拷問：你有對象嗎？

沒有，但我可以 new 一個！

public class GirlFriend {

private String name;

private int age;

// 省略 getter & setter ...

public satic void main(String[] args) {

GirlFriend myGirlFriend = new GirlFriend();

myGirlFriend.setName("小美");

myGirlFriend.setAge(18);

}

}

但如果對象的屬性太多，咋辦？

public class GirlFriend {

private String name;

private int age;

private int bust;

private int waist;

private int hips;

private List hobby;

private String birthday;

private String address;

private String mobile;

private String email;

private String hairColor;

private Map gift;

// 等等等等 ...

// 省略 getter & setter ...

public static void main(String[] args) {

GirlFriend myGirlFriend = new GirlFriend();

myGirlFriend.setName("小美");

myGrlFriend.setAge(18);

myGirlFriend.setBust(33);

myGirlFriend.setWaist(23);

myGirlFriend.setHips(33);

myGirlFriend.setBirthday("2001-10-26");

myGirlFriend.setAddress("上海浦東");

myGirlFriend.setMobile("18688888888");

myGirlFriend.setEmail("pretty-xiaomei@qq.com");

myGirlFriend.setHairColor("淺棕色帶點微卷");

List hobby = new ArrayList<>();

hobby.add("逛街");

hobby.add("購物");

hobby.add("買東西");

myGirlFriend.setHobby(hobby);

Map gift = new HashMap<>();

gift.put("情人節禮物", "LBR 1912女王時代");

gift.put("生日禮物", "迪奧烈焰藍金");

gift.put("紀念日禮物", "阿瑪尼紅管唇釉");

myGirlFriend.setGift(gift);

// 等等等等 ...

}

}

GirlFriend

GirlFriend{name='小美'

, age=18

, bust=33

, waist=23

, hips=33

, hobby=[逛街, 購物, 買東西]

, birthday='2001-10-26'

, address='上海浦東'

, mobile='18688888888'

, email='pretty-xiaomei@qq.com'

, hairColor='淺棕色帶點微卷'

, gift={情人節禮物=LBR 1912女王時代, 生日禮物=迪奧烈焰藍金, 紀念日禮物=阿瑪尼紅管唇釉}

}

GirlFriend 是很美，但寫起來也太麻煩了吧。

說說缺點：實例化和設置屬性分開，不好維護；變量名重復寫。

莫慌，看法寶~

這里不再介紹其他 Builder 實現方式，直接祭出最實用的通用Builder：

適用于所有類，不需要改造原來類，不需要 lombok 插件支持。

先看看使用姿勢：

public class GirlFriend {

// 省略屬性 ...

// 省略 getter & setter ...

// 為了演示方便，加幾個聚合方法

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, "上海浦東")

.with(GirlFriend::setMobile, "18688888888")

.with(GirlFriend::setEmail, "pretty-xiaomei@qq.com")

.with(GirlFriend::setHairColor, "淺棕色帶點微卷")

.with(GirlFriend::addHobby, "逛街")

.with(GirlFriend::addHobby, "購物")

.with(GirlFriend::addHobby, "買東西")

.with(GirlFriend::addGift, "情人節禮物", "LBR 1912女王時代")

.with(GirlFriend::addGift, "生日禮物", "迪奧烈焰藍金")

.with(GirlFriend::addGift, "紀念日禮物", "阿瑪尼紅管唇釉")

// 等等等等 ...

.build();

}

}

看到了嗎！實例化和屬性設置在同一條語句執行，鏈式操作，一路點點點，清爽！

Talk is cheap, show me the code：

/**

* 通用的 Builder 模式構建器

*

* @author: CipherCui

* @since 2019/8/29

*/

public class Builder {

private final Supplier instantiator;

private List> modifiers = new ArrayList<>();

public Builder(Supplier instantiator) {

this.instantiator = instantiator;

}

public static Builder of(Supplier instantiator) {

return new Builder<>(instantiator);

}

public Builder with(Consumer1 consumer, P1 p1) {

Consumer c = instance -> consumer.accept(instance, p1);

modifiers.add(c);

return this;

}

public Builder with(Consumer2 consumer, P1 p1, P2 p2) {

Consumer c = instance -> consumer.accept(instance, p1, p2);

modifiers.add(c);

return this;

}

public Builder with(Consumer3 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 參數 Consumer

*/

@FunctionalInterface

public interface Consumer1 {

void accept(T t, P1 p1);

}

/**

* 2 參數 Consumer

*/

@FunctionalInterface

public interface Consumer2 {

void accept(T t, P1 p1, P2 p2);

}

/**

* 3 參數 Consumer

*/

@FunctionalInterface

public interface Consumer3 {

void accept(T t, P1 p1, P2 p2, P3 p3);

}

}

這個示例最多支持三個參數的設置屬性方法，也完全夠用了。如果要擴展也很容易，依葫蘆畫瓢，添加多個參數的Consumer。

快用你的 Builder 建個對象吧~

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