你还在 new 对象吗？Java8 通用 Builder 了解一下？
点击下方“IT牧场”，选择“设为星标”
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<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 ...
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<String> hobby = new ArrayList<>();
hobby.add("逛街");
hobby.add("购物");
hobby.add("买东西");
myGirlFriend.setHobby(hobby);
Map<String, String> 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{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<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。
快用你的 Builder 建个对象吧~
来源：ciphermagic.cn/java8-builder.html
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