目标：

将复杂对象的创建过程和对象的表现分离，从而相同的创建步骤可以生成不同表现的对象。

静态类图：

生成器模式.png

Talk Is Simple:

Demo: 快餐店儿童套餐，套餐主要包含一个主食、一个甜点、一份饮料、一个小玩具。假设，目前快餐店针对小男孩和小女孩推出了两套不同的套餐！利用Builder设计模式实现如下：

/**
    儿童套餐
**/
public class ChildrenMeal{
    private String mainItem;
    private String sideItem;
    private String drink;
    private String toy;
    /**
        sets 方法
    **/
}
/**
  抽象构造者
**/
public abstract class MealBuilder{
    private ChildrenMeal childrenMeal;
    public ChildrenMeal getMeal(){return this.childrenMeal;}
    public abstract void prepareMainItem();
    public abstract void prepareSideItem();
    public abstract void prepareDrink();
    public abstract void prepareToy();
}
public class BoyMealBuilder extends MealBuilder{
    public BoyMealCashier(){
        this.childrenMeal = new ChildrenMeal();
    }
    public void prepareMainItem(){
        System.out.println("男娃套餐主食是鸡腿堡");
    }
    public void prepareSideItem(){
        System.out.println("男娃套餐甜点是薯条");
    }
    public void prepareDrink(){
        System.out.println("男娃套餐饮料是可乐");
    }
    public void prepareToy(){
        System.out.println("男娃玩具是恐龙玩具");
    }
    
}
public class GirlMealBuilder{
    public BoyMealCashier(){
        this.childrenMeal = new ChildrenMeal();
    }
    public void prepareMainItem(){
        System.out.println("女娃套餐主食是蔬菜堡");
    }
    public void prepareSideItem(){
        System.out.println("女娃套餐甜点是甜甜圈");
    }
    public void prepareDrink(){
        System.out.println("女娃套餐饮料是杯橙汁");
    }
    public void prepareToy(){
        System.out.println("女娃套餐玩具是芭比娃娃");
    }
}
/*Director */
public class Cashier{
    private MealBuilder builder;
    public void setBuilder(MealBuilder builder){
        this.builder = builder;
    }
    public ChildrenMeal getChildrenMeal(){
        builder.prepareMainItem();
        builder.prepareSideItem();
        builder.prepareDrink();
        builder.preapreToy();
    }
}
public class Main{
    public static void main(String args[]){
        Cashier cashier = new Cashier();
        cashier.setBuilder(new BoyMealBuilder());
        ChildrenMeal meal = cashier.getChildrenMeal();
    }
}

变形：

如上模式的Builder模式中，产品的构建步骤的顺序以及每个步骤的实现方式分别在Director 和具体的Builder类限定了，当某一天小女汉子非要恐龙不喜欢芭比娃娃,要吃鸡腿堡，需要为个性化的需求提供一个专用的Builder实现类，为支持客户端的灵活性，需要改造！

public abstract class MealBuilder{
    private ChildrenMeal meal;
    
    public ChildrenMeal getMeal(){return this.meal;}
    public abstract Builder prepareMainItem(String msg);
    public abstract Builder prepareSideItem(String msg);
    public abstract Builder prepareDrink(String msg);
    public abstract Builder prepareToy(String msg);
}
public class ConcreteMealBuilder extends MealBuilder{
    public ConcreteMealBuilder(){
       this.meal = new ChildrenMeal();
   }
 
   public Builder prepareMainItem(String msg){
       this.meal.setMainItem(msg);
       return this;
   }
   public Builder prepareSideItem(String msg){
       this.meal.setSideItem(msg);
       return this;
   }
    public Builder prepareDrink(String msg){
        this.meal.setDrink(msg);
        return this;
    }
    public Builder prepareToy(String msg){
        this.meal.setToy(msg);
        return this;
    }
}
/**
    儿童套餐
**/
public class ChildrenMeal{
    private String mainItem = "鸡腿堡";
    private String sideItem = "甜甜圈";
    private String drink = "橙汁";
    private String toy ="芭比娃娃";
    /**
        sets 方法
    **/
}
public class Children{
    public static void main(String args[]){
        ConcreateBuilder cashier = new ConcreateBuilder();
        cashier.setMainItem("鸡腿堡").setToy("恐龙");
    }
}