作者：cipher
www.ciphermagic.cn/java8-builder.html

第1-30期：30期Java項(xiàng)目整理

程序員經(jīng)常會(huì)遇到靈魂拷問：你有對(duì)象嗎？

沒有，但我可以 new 一個(gè)！

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);    }}

沒問題，老鐵！但如果對(duì)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");        myGirlFriend.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("[email protected]");        myGirlFriend.setHairColor("淺棕色帶點(diǎn)微卷");        List hobby = new ArrayList<>();        hobby.add("逛街");        hobby.add("購(gòu)物");        hobby.add("買東西");        myGirlFriend.setHobby(hobby);        Map gift = new HashMap<>();        gift.put("情人節(jié)禮物", "LBR 1912女王時(shí)代");        gift.put("生日禮物", "迪奧烈焰藍(lán)金");        gift.put("紀(jì)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(gòu)物, 買東西], birthday='2001-10-26', address='上海浦東', mobile='18688888888', email='[email protected]', hairColor='淺棕色帶點(diǎn)微卷', gift={情人節(jié)禮物=LBR 1912女王時(shí)代, 生日禮物=迪奧烈焰藍(lán)金, 紀(jì)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(diǎn)：實(shí)例化和設(shè)置屬性分開，不好維護(hù)；變量名重復(fù)寫。

莫慌，看法寶~

這里不再介紹其他 Builder 實(shí)現(xiàn)方式，直接祭出最實(shí)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(shì)：

public class GirlFriend {    // 省略屬性 ...    // 省略 getter & setter ...

    // 為了演示方便，加幾個(gè)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, "[email protected]")                .with(GirlFriend::setHairColor, "淺棕色帶點(diǎn)微卷")                .with(GirlFriend::addHobby, "逛街")                .with(GirlFriend::addHobby, "購(gòu)物")                .with(GirlFriend::addHobby, "買東西")                .with(GirlFriend::addGift, "情人節(jié)禮物", "LBR 1912女王時(shí)代")                .with(GirlFriend::addGift, "生日禮物", "迪奧烈焰藍(lán)金")                .with(GirlFriend::addGift, "紀(jì)念日禮物", "阿瑪尼紅管唇釉")                // 等等等等 ...                .build();    }}

看到了嗎！實(shí)例化和屬性設(shè)置在同一條語(yǔ)句執(zhí)行，鏈?zhǔn)讲僮?，一路點(diǎn)點(diǎn)點(diǎn)，清爽！

Talk is cheap, show me the code：

/** * 通用的 Builder 模式構(gòu)建器 * * @author: CipherCui * @since 2019/8/29 */public class Builder<T> {    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(shù) Consumer     */    @FunctionalInterface    public interface Consumer1<T, P1> {        void accept(T t, P1 p1);    }    /**     * 2 參數(shù) Consumer     */    @FunctionalInterface    public interface Consumer2<T, P1, P2> {        void accept(T t, P1 p1, P2 p2);    }    /**     * 3 參數(shù) Consumer     */    @FunctionalInterface    public interface Consumer3<T, P1, P2, P3> {        void accept(T t, P1 p1, P2 p2, P3 p3);    }}

這個(gè)示例最多支持三個(gè)參數(shù)的設(shè)置屬性方法，也完全夠用了。如果要擴(kuò)展也很容易，依葫蘆畫瓢，添加多個(gè)參數(shù)的Consumer。

快用你的 Builder 建個(gè)對(duì)象吧~

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