你還在 new 物件嗎？Java 8 通用 Builder 了解一下...

2024-04-23碼農

程式設計師經常會遇到靈魂拷問：你有物件嗎？

沒有，但我可以 new 一個！

public classGirlFriend{ private String name; privateint age; // 省略 getter & setter ... publicstaticvoidmain(String[] args){ GirlFriend myGirlFriend = new GirlFriend(); myGirlFriend.setName("小美"); myGirlFriend.setAge(18); } }

沒問題，老鐵！但如果物件的內容太多，咋辦？

public classGirlFriend{ private String name; privateint age; privateint bust; privateint waist; privateint hips; private List<String> hobby; private String birthday; private String address; private String mobile; private String email; private String hairColor; private Map<String, String> gift; // 等等等等 ... // 省略 getter & setter ... publicstaticvoidmain(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("公眾號：一行Java"); myGirlFriend.setMobile("18688888888"); myGirlFriend.setEmail("[email protected]"); myGirlFriend.setHairColor("淺棕色帶點微卷"); List<String> hobby = new ArrayList<>(); hobby.add("逛街"); hobby.add("購物"); hobby.add("買東西"); myGirlFriend.setHobby(hobby); Map<String, String> 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{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='[email protected]' , 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：例項化和設定內容分開，不好維護；變量名重復寫。

莫慌，看法寶~

這裏不再介紹其他 Builder 實作方式，直接祭出最實用的 通用Builder ：

適用於所有類，不需要改造原來類，不需要 lombok 外掛程式支持。

先看看使用姿勢：

public classGirlFriend{ // 省略內容 ... // 省略 getter & setter ... // 為了演示方便，加幾個聚合方法 publicvoidaddHobby(String hobby){ this.hobby = Optional.ofNullable(this.hobby).orElse(new ArrayList<>()); this.hobby.add(hobby); } publicvoidaddGift(String day, String gift){ this.gift = Optional.ofNullable(this.gift).orElse(new HashMap<>()); this.gift.put(day, gift); } publicvoidsetVitalStatistics(int bust, int waist, int hips){ this.bust = bust; this.waist = waist; this.hips = hips; } publicstaticvoidmain(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, "[email protected]") .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！例項化和內容設定在同一條語句執行，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 * */ public classBuilder<T> { privatefinal Supplier<T> instantiator; private List<Consumer<T>> modifiers = new ArrayList<>(); publicBuilder(Supplier<T> instantiator){ this.instantiator = instantiator; } publicstatic <T> Builder<T> of(Supplier<T> instantiator){ returnnew Builder<>(instantiator); } public <P1> Builder<T> with(Consumer1<T, P1> consumer, P1 p1){ Consumer<T> c = instance -> consumer.accept(instance, p1); modifiers.add(c); returnthis; } public <P1, P2> Builder<T> with(Consumer2<T, P1, P2> consumer, P1 p1, P2 p2){ Consumer<T> c = instance -> consumer.accept(instance, p1, p2); modifiers.add(c); returnthis; } public <P1, P2, P3> Builder<T> with(Consumer3<T, P1, P2, P3> consumer, P1 p1, P2 p2, P3 p3){ Consumer<T> c = instance -> consumer.accept(instance, p1, p2, p3); modifiers.add(c); returnthis; } public T build(){ T value = instantiator.get(); modifiers.forEach(modifier -> modifier.accept(value)); modifiers.clear(); return value; } /** * 1 參數 Consumer */ @FunctionalInterface publicinterfaceConsumer1<T, P1> { voidaccept(T t, P1 p1); } /** * 2 參數 Consumer */ @FunctionalInterface publicinterfaceConsumer2<T, P1, P2> { voidaccept(T t, P1 p1, P2 p2); } /** * 3 參數 Consumer */ @FunctionalInterface publicinterfaceConsumer3<T, P1, P2, P3> { voidaccept(T t, P1 p1, P2 p2, P3 p3); } }