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你还在 new 对象吗?Java8 通用 Builder 了解一

你还在 new 对象吗?Java8 通用 Builder 了解一

作者: 码农突围 | 来源:发表于2021-01-28 18:27 被阅读0次

    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 Listhobby;
      private String birthday;
      private String address;
      private String mobile;
      private String email;
      private String hairColor;
      private Mapgift;
      // 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");
        Listhobby = new ArrayList<>();
        hobby.add("逛街");
        hobby.add("购物");
        hobby.add("买东西");
        myGirlFriend.setHobby(hobby);
        Mapgift = 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 Supplierinstantiator;
      private List<consumer> modifiers = new ArrayList<>();
      public Builder(Supplierinstantiator){
        this.instantiator = instantiator;
      }
      public staticBuilderof(Supplierinstantiator){
        return new Builder<>(instantiator);
      }
      publicBuilderwith(Consumer1consumer, P1 p1){
        Consumerc = instance -> consumer.accept(instance, p1);
        modifiers.add(c);
        return this;
      }
      publicBuilderwith(Consumer2consumer, P1 p1, P2 p2){
        Consumerc = instance -> consumer.accept(instance, p1, p2);
        modifiers.add(c);
        return this;
      }
      publicBuilderwith(Consumer3consumer, P1 p1, P2 p2, P3 p3){
        Consumerc = 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~

    来自:rrd.me/gtQTp

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