聽說你還在new 對象？Java8通用Builder不了解一下？

程式設計師經常會遇到靈魂拷問：你有對象嗎？

沒有，但我可以 new 一個！

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<String> hobby;
    private String birthday;
    private String address;
    private String mobile;
    private Stringe mail;
    private Stringhair Color;
    private Map <String,String> gift;
    //等等等等...
    //省略getter&setter...
    publicstaticvoidmain(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("pretty-xiaomei@qq.com");
        myGirlFriend.setHairColor("淺棕色帶點微卷");
        List<String>hobby=newArrayList<>();
        hobby.add("逛街");
        hobby.add("購物");
        hobby.add("買東西");
        myGirlFriend.setHobby(hobby);
        Map<String,String>gift=newHashMap<>();
        gift.put("情人節禮物","LBR1912女王時代");
        gift.put("生日禮物","迪奧烈焰藍金");
        gift.put("紀念日禮物","阿瑪尼紅管唇釉");
        myGirlFriend.setGift(gift);
        //等等等等...
    }
}

GirlFriend{name='小美'
  ,age=18
  ,bust=33
  ,waist=23
  ,hips=33
  ,hobby=[逛街,購物,買東西]
  ,birthday='2001-10-26'
  ,address='上海浦東'
  ,mobile='18688888888'
  ,email='pretty-xiaomei@qq.com'
  ,hairColor='淺棕色帶點微卷'
  ,gift={情人節禮物=LBR1912女王時代,生日禮物=迪奧烈焰藍金,紀念日禮物=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：實例化和設置屬性分開，不好維護；變量名重複寫。

莫慌，看法寶~

這裡不再介紹其他 Builder 實現方式，直接祭出最實用的通用Builder：

適用於所有類，不需要改造原來類，不需要 lombok 插件支持。

先看看使用姿勢：

publicclassGirlFriend{
    //省略屬性...
    //省略getter&setter...

    //為了演示方便，加幾個聚合方法
    publicvoidaddHobby(Stringhobby){
      this.hobby=Optional.ofNullable(this.hobby).orElse(newArrayList<>());
      this.hobby.add(hobby);
    }
    publicvoidaddGift(Stringday,Stringgift){
      this.gift=Optional.ofNullable(this.gift).orElse(newHashMap<>());
      this.gift.put(day,gift);
    }
    publicvoidsetVitalStatistics(intbust,intwaist,inthips){
      this.bust=bust;
      this.waist=waist;
      this.hips=hips;
    }
    publicstaticvoidmain(String[]args){
        GirlFriendmyGirlFriend=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,"pretty-xiaomei@qq.com")
        .with(GirlFriend::setHairColor,"淺棕色帶點微卷")
        .with(GirlFriend::addHobby,"逛街")
        .with(GirlFriend::addHobby,"購物")
        .with(GirlFriend::addHobby,"買東西")
        .with(GirlFriend::addGift,"情人節禮物","LBR1912女王時代")
        .with(GirlFriend::addGift,"生日禮物","迪奧烈焰藍金")
        .with(GirlFriend::addGift,"紀念日禮物","阿瑪尼紅管唇釉")
        //等等等等...
        .build();
    }
}

看到了嗎！實例化和屬性設置在同一條語句執行，鏈式操作，一路點點點，清爽！

Talk is cheap, show me the code：

/**
*通用的Builder模式構建器
*
*@author:CipherCui
*@since2019/8/29
*/
public class Builder<T>{
    private final Supplier<T>instantiator;
    private List<Consumer<T>> modifiers=newArrayList<>();
    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,P1p1){
    Consumer<T>c=instance->consumer.accept(instance,p1);
    modifiers.add(c);
    return this;
  }
  public <P1,P2>Builder<T>with(Consumer2<T,P1,P2>consumer,P1p1,P2p2){
    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,P1p1,P2p2,P3p3){
    Consumer<T>c=instance->consumer.accept(instance,p1,p2,p3);
    modifiers.add(c);
    return this;
  }
  public T build(){
    Tvalue=instantiator.get();
    modifiers.forEach(modifier->modifier.accept(value));
    modifiers.clear();
    return value;
  }
  /**
  *1參數Consumer
  */
  @FunctionalInterface
  public interface Consumer1<T,P1>{
        void accept(Tt,P1p1);
  }
  /**
  *2參數Consumer
  */
  @FunctionalInterface
  public interface Consumer2<T,P1,P2>{
        void accept(Tt,P1p1,P2p2);
  }
  /**
  *3參數Consumer
  */
  @FunctionalInterface
  public interface Consumer3<T,P1,P2,P3>{
        void accept(Tt,P1p1,P2p2,P3p3);
  }
}

這個示例最多支持三個參數的設置屬性方法，也完全夠用了。如果要擴展也很容易，依葫蘆畫瓢，添加多個參數的Consumer。

快用你的 Builder 建個對象吧~