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

第1-30期：30期Java项目整理

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 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("上海浦东");        myGirlFriend.setMobile("18688888888");        myGirlFriend.setEmail("pretty-xiaomei@qq.com");        myGirlFriend.setHairColor("浅棕色带点微卷");        List hobby = new ArrayList<>();        hobby.add("逛街");        hobby.add("购物");        hobby.add("买东西");        myGirlFriend.setHobby(hobby);        Map gift = 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 

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 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 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~

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