听说你还在new 对象?Java8通用Builder不了解一下?

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 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("上海浦东");
        myGirlFriend.setMobile("18688888888");
        myGirlFriend.setEmail("pretty-xiaomei@qq.com");
        myGirlFriend.setHairColor("浅棕色带点微卷");
        List<String>hobby=newArrayList<>();
        hobby.add("逛街");
        hobby.add("购物");
        hobby.add("买东西");
        myGirlFriend.setHobby(hobby);
        Map<String,String>gift=newHashMap<>();
        gift.put("情人节礼物","LBR1912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=LBR1912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：

publicclassGirlFriend{
    //省略属性...
    //省略getter&setter...

    //为了演示方便，加几个聚合方法
    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","LBR1912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
*@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;
  }
  /**
  *1参数Consumer
  */
  @FunctionalInterface
  public interface Consumer1<T,P1>{
  	void accept(Tt,P1p1);
  }
  /**
  *2参数Consumer
  */
  @FunctionalInterface
  public interface Consumer2<T,P1,P2>{
  	void accept(Tt,P1p1,P2p2);
  }
  /**
  *3参数Consumer
  */
  @FunctionalInterface
  public interface Consumer3<T,P1,P2,P3>{
  	void accept(Tt,P1p1,P2p2,P3p3);
  }
}

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~