别名：创建者模式
建造者模式针对复杂对象，分离它们的构建与表示，达到同样构建过程创建不同表示的目的。
建造者模式封装了复杂对象的构建过程，通过子类继承或者重载的方式，动态的创建具有复合属性的对象。

传统模式

就拿做三明治来举例，首先定义三明治的抽象类

@Data
public class Sandwich {private String bread;private String meat;private List<String> veg;private String source;public Sandwich(String bread, String meat) {this.bread = bread;this.meat = meat;}
}

然后定义抽象的Builder

public abstract class SandwichBuilder {public abstract void setVeg();public abstract void setSource();public abstract Sandwich getSandwich();
}

现在提供两种实现

public class TunaSandwichBuilder extends SandwichBuilder {private Sandwich sandwich;public TunaSandwichBuilder(String bread) {this.sandwich = new Sandwich(bread, "金枪鱼");}@Overridepublic void setVeg() {sandwich.setVeg(Arrays.asList("番茄", "黄瓜", "生菜"));}@Overridepublic void setSource() {sandwich.setSource("番茄酱");}@Overridepublic Sandwich getSandwich() {return sandwich;}
}public class SirloinSandwichBuilder extends SandwichBuilder {private Sandwich sandwich;public SirloinSandwichBuilder(String bread) {this.sandwich = new Sandwich(bread, "牛腩");}@Overridepublic void setVeg() {sandwich.setVeg(Arrays.asList("青椒", "酱瓜"));}@Overridepublic void setSource() {sandwich.setSource("千岛酱");}@Overridepublic Sandwich getSandwich() {return sandwich;}
}

然后定义一个指挥官

public class SandwichDirector {public void makeSandwich(SandwichBuilder builder){builder.setVeg();builder.setSource();}
}

调用的时候

public class SandwichMaker {public static void main(String[] args) {SandwichDirector director = new SandwichDirector();SandwichBuilder builder = new TunaSandwichBuilder("燕麦面包");director.makeSandwich(builder);Sandwich tunaSandwich = builder.getSandwich();System.out.println(tunaSandwich);builder = new SirloinSandwichBuilder("全麦面包");director.makeSandwich(builder);Sandwich sirSandwich = builder.getSandwich();System.out.println(sirSandwich);}
}

类JDK8的Builder

对类Sandwich做改造

@ToString
public class Sandwich {private String bread;private String meat;private List<String> veg;private String source;private Sandwich(Builder builder) {this.bread = builder.bread;this.meat = builder.meat;this.veg = builder.veg;this.source = builder.source;}public static class Builder{private String bread;private String meat;private List<String> veg;private String source;public Builder(String bread, String meat) {this.bread = bread;this.meat = meat;}public Builder veg(List<String> veg){this.veg = veg;return this;}public Builder source(String source){this.source = source;return this;}public Sandwich build(){return new Sandwich(this);}}
}

调用时就可以使用连续构造的哲学

public class BuildDemo {public static void main(String[] args) {Sandwich sandwich = new Sandwich.Builder("蜂蜜面包", "鸡胸肉").veg(Arrays.asList("洋葱", "胡萝卜")).source("BBQ").build();System.out.println(sandwich);}
}