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Builder一个对象

一般新建对象我们都是直接new一下

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<String> hobby;
// 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);
    // 等等等等 ...
}

}

而Java8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<T> instantiator;
private List<Consumer<T>> modifiers = new ArrayList<>();
public Builder(Supplier<T> instantiator) {
    this.instantiator = instantiator;
}
public static <T> Builder<T> of(Supplier<T> instantiator) {
    return new Builder<>(instantiator);
}
public <P1> Builder<T> with(Consumer1<T, P1> consumer, P1 p1) {
    Consumer<T> c = instance -> consumer.accept(instance, p1);
    modifiers.add(c);
    return this;
}
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);
    return this;
}
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);
    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。

参考： http://www.ciphermagic.cn/jav...

原文 https://segmentfault.com/a/1190000021600981

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