JAVA架构师之路十五：设计模式之策略模式

article/2025/9/29 11:09:08

JAVA架构师之路十四：设计模式之模板模式

策略模式

- 1. 策略模式
- 2. 优惠券案例
- 3. 支付案例

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1. 策略模式

定义

策略模式又叫政策模式，它是将定义的算法家族，分别封装起来，让它们之间可以互相替换，从而让算法的变化不会影响到使用算法的用户。

可以避免多重分支的if 。。。。else 和switch语句。

属于行为型模式

适用场景

假如系统中有很多的类，而他们的区别仅仅在于他们的行为不同。

一个系统需要动态地在几种算法中选择一种

需要屏蔽算法规则

优点

策略模式符合开闭原则

避免使用多出个的条件转移语句，如if … else 、switch语句

使用策略模式可以提高算法的保密性和安全性。

缺点

客户端必须要知道所有的策略，并且自己决定执行使用哪一个策略类

代码中会产生非常多的策略类，增加维护难度

2. 优惠券案例

网购中有很多优惠策略，那么这种场景非常适合策略模式

public interface IPromotionStrategy {void doPromotion();
}

public class CashbackStrategy implements IPromotionStrategy {public void doPromotion() {System.out.println("返现,直接打款到支付宝账号");}
}

public class CouponStrategy implements IPromotionStrategy {public void doPromotion() {System.out.println("使用优惠券抵扣");}
}

public class EmptyStrategy implements IPromotionStrategy {public void doPromotion() {System.out.println("无优惠");}
}

public class GroupBuyStrategy implements IPromotionStrategy {public void doPromotion() {System.out.println("5人团购, 可以优惠");}
}

public class PromotionFactory {private static Map<String, IPromotionStrategy> PROMIOTIONS = new HashMap<String, IPromotionStrategy>();private static final IPromotionStrategy EMPTY = new EmptyStrategy();static {PROMIOTIONS.put(PromotionKey.CASHBACK, new CashbackStrategy());PROMIOTIONS.put(PromotionKey.COUPON, new CouponStrategy());PROMIOTIONS.put(PromotionKey.GROUPBUY, new GroupBuyStrategy());}public static IPromotionStrategy getPromiotion(String promotion) {if (PROMIOTIONS.containsKey(promotion)) {return PROMIOTIONS.get(promotion);}return EMPTY;}private interface PromotionKey {String COUPON = "COUPON";String CASHBACK = "CASHBACK";String GROUPBUY = "GROUPBUY";}public static Set<String> getPromotionKeys(){return PROMIOTIONS.keySet();}
}

public class Test {public static void main(String[] args) {Set<String> promotions = PromotionFactory.getPromotionKeys();System.out.println("所有支付方式:" + promotions.toString());String promotion = "COUPON";IPromotionStrategy strategy = PromotionFactory.getPromiotion(promotion);strategy.doPromotion();promotion = "CASHBACK";strategy = PromotionFactory.getPromiotion(promotion);strategy.doPromotion();}
}

所有支付方式:[CASHBACK, COUPON, GROUPBUY]
使用优惠券抵扣
返现,直接打款到支付宝账号

在这里插入图片描述

3. 支付案例

最典型的策略模式就是支付。现在网购支付方式多种多样，不同的支付方式都有不同背后算法。

public class MsgResult {private int code;private String msg;private Object data;public MsgResult(int code, String msg, Object data) {this.code = code;this.msg = msg;this.data = data;}@Overridepublic String toString() {return "MsgResult{" +"code=" + code +", msg='" + msg + '\'' +", data=" + data +'}';}
}

public abstract class Payment {public MsgResult pay(String uid, double amount) {if (queryBlance(uid) < amount) {return new MsgResult(500, "支付失败", "余额不足");}return new MsgResult(0, "支付成功", "支付金额: " + amount);}protected abstract double queryBlance(String uid);protected abstract String getName();
}

public class AliPay extends Payment {@Overridepublic double queryBlance(String uid) {return 1000;}@Overridepublic String getName() {return "支付宝";}
}

public class JDPay extends Payment {@Overridepublic double queryBlance(String uid) {return 900;}@Overridepublic String getName() {return "京东支付";}
}

public class YunShanPay extends Payment {@Overridepublic double queryBlance(String uid) {return 500;}@Overridepublic String getName() {return "云闪付";}
}

public class PayStrategy {public static final String ALI_PAY = "ALI_PAY";public static final String JD_PAY = "JD_PAY";public static final String YUNSHAN_PAY = "YUNSHAN_PAY";public static final String DEFAULT_PAY = ALI_PAY;private static Map<String, Payment> strategy = new HashMap<String, Payment>();static {strategy.put(ALI_PAY, new AliPay());strategy.put(JD_PAY, new JDPay());strategy.put(YUNSHAN_PAY, new YunShanPay());}public static Payment getPayment(String payKey) {if (strategy.containsKey(payKey)) {return strategy.get(payKey);}return strategy.get(DEFAULT_PAY);}
}

public class Order {private String uid;private String orderId;private double amount;public Order(String uid, String orderId, double amount) {this.uid = uid;this.orderId = orderId;this.amount = amount;}public MsgResult pay() {return pay(PayStrategy.DEFAULT_PAY);}public MsgResult pay(String payKey) {Payment payment = PayStrategy.getPayment(payKey);System.out.println("欢迎使用: " + payment.getName() + "支付");System.out.println("本次交意金额: " + amount + "开始支付");return payment.pay(uid, amount);}
}

public class Test {public static void main(String[] args) {Order order = new Order("1", "202012160909", 999);System.out.println(order.pay());System.out.println(order.pay(PayStrategy.JD_PAY));System.out.println(order.pay(PayStrategy.YUNSHAN_PAY));}
}

欢迎使用: 支付宝支付
本次交意金额: 999.0开始支付
MsgResult{code=0, msg='支付成功', data=支付金额: 999.0}
欢迎使用: 京东支付支付
本次交意金额: 999.0开始支付
MsgResult{code=500, msg='支付失败', data=余额不足}
欢迎使用: 云闪付支付
本次交意金额: 999.0开始支付
MsgResult{code=500, msg='支付失败', data=余额不足}