B03 策略模式 示例

示例类图

策略模式.png

示例代码

抽象策略

public interface PromotionStrategy {
    void doPromotion();
}

具体策略

public class EmptyPromotionStrategy implements PromotionStrategy {
    @Override
    public void doPromotion() {
        System.out.println("无促销活动");
    }
}

public class FanXianPromotionStrategy implements PromotionStrategy {
    @Override
    public void doPromotion() {
        System.out.println("返现促销,返回的金额存放到慕课网用户的余额中");
    }
}

public class LiJianPromotionStrategy implements PromotionStrategy {
    @Override
    public void doPromotion() {
        System.out.println("立减促销,课程的价格直接减去配置的价格");
    }
}

public class ManJianPromotionStrategy implements PromotionStrategy{
    @Override
    public void doPromotion() {
        System.out.println("满减促销,满200-20元");
    }
}

策略使用者

public class PromotionActivity {

    private PromotionStrategy promotionStrategy;

    public PromotionActivity(PromotionStrategy promotionStrategy) {
        this.promotionStrategy = promotionStrategy;
    }

    public void executePromotionStrategy(){
        promotionStrategy.doPromotion();
    }

}

策略工厂

import java.util.HashMap;
import java.util.Map;

public class PromotionStrategyFactory {

    private static Map<String, PromotionStrategy>
            PROMOTION_STRATEGY_MAP = new HashMap<String, PromotionStrategy>();

    static {
        PROMOTION_STRATEGY_MAP.put(PromotionKey.LIJIAN,
                new LiJianPromotionStrategy());
        PROMOTION_STRATEGY_MAP.put(PromotionKey.FANXIAN,
                new FanXianPromotionStrategy());
        PROMOTION_STRATEGY_MAP.put(PromotionKey.MANJIAN,
                new ManJianPromotionStrategy());
    }

    private static final PromotionStrategy
            NON_PROMOTION = new EmptyPromotionStrategy();

    private PromotionStrategyFactory(){}

    public static PromotionStrategy getPromotionStrategy(String promotionKey){
        PromotionStrategy promotionStrategy =
                PROMOTION_STRATEGY_MAP.get(promotionKey);
        return promotionStrategy == null ? NON_PROMOTION : promotionStrategy;
    }

    private interface PromotionKey{
        String LIJIAN = "LIJIAN";
        String FANXIAN = "FANXIAN";
        String MANJIAN = "MANJIAN";
    }

}

客户端

• 主要看第三个main方法，其示例了策略模式如何替换掉大量的if ... else ...；
• 客户端是面向使用策略的角色（PromotionActivity）编程的；
• promotionKey 可以看成是 if ... else ... 中传入的参数，策略模式配合享元模式，将原来在每个判断分支中现new，变成在工厂类中都先new好，然后根据传入 if ... else ... 的参数去工厂里取；

public class Test {

//    public static void main(String[] args) {
//        PromotionActivity promotionActivity618 = new PromotionActivity(new LiJianPromotionStrategy());
//        PromotionActivity promotionActivity1111 = new PromotionActivity(new FanXianPromotionStrategy());
//
//        promotionActivity618.executePromotionStrategy();
//        promotionActivity1111.executePromotionStrategy();
//    }

//    public static void main(String[] args) {
//        PromotionActivity promotionActivity = null;
//
//        String promotionKey = "LIJIAN";
//
//        if(StringUtils.equals(promotionKey,"LIJIAN")){
//            promotionActivity = new PromotionActivity(new LiJianPromotionStrategy());
//        }else if(StringUtils.equals(promotionKey,"FANXIAN")){
//            promotionActivity = new PromotionActivity(new FanXianPromotionStrategy());
//        }//......
//        promotionActivity.executePromotionStrategy();
//    }


    public static void main(String[] args) {
        String promotionKey = "MANJIANxxx";
        PromotionActivity promotionActivity =
                new PromotionActivity(
                        PromotionStrategyFactory.getPromotionStrategy(promotionKey)
                );
        promotionActivity.executePromotionStrategy();
    }

}

输出：

无促销活动