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• 怎么把策略模式和工厂模式结合起来使用

如果大家对策略模式和工厂模式不是很了解的话可以先看前面文章
策略模式：https://www.jianshu.com/p/958281936901
工厂模式：https://www.jianshu.com/p/9078481e00c6

大家可能都用过微信支付，在使用微信支付付钱时候：

1、当我们的付款金额大于我们的余额时，会让我们使用银行卡支付，
2、余额充足的时候会让我们优先使用余额里面的钱
扣款策略一：
余额(blance) >= 付款金额(tradeamout) 使用余额
扣款策略二：
余额(blance) < 付款金额(tradeamout) 使用银行卡
很明显这是一个策略模式的实际应用，但是你还记得策略模式的缺陷吗？它的具体策略必须暴露出去，而且还要由上层模块初始化，这不适合，与迪米特法则不符( 迪米特法则（law of demeter）又叫作最少知识原则（least knowledge principle 简写lkp），就是说一个对象应当对其他对象有尽可能少的了解,不和陌生人说话。注：摘自百度百科，这个迪米特法则下次再细讲)冲突。高层模块对底层模块仅仅在接触层次上，而不应该是耦合关系。问题出了，我们应该想办法解决，正好工厂模式可以帮我们解决这个问题。但是引入工厂模式也有问题，工厂方法要指定一个类，它才能生产对象，我们用枚举来完成。
首先我们先建两个实体类wxblance和wxtrade

import java.math.bigdecimal;/*** @author shuliangzhao* @title: wxblance* @projectname design-parent* @description: todo* @date 2019/5/28 23:50*/ public class wxblance {//余额private bigdecimal blance;public bigdecimal getblance() {return blance;}public void setblance(bigdecimal blance) {this.blance = blance;} } import java.math.bigdecimal;/*** @author shuliangzhao* @title: trade* @projectname design-parent* @description: todo* @date 2019/5/28 23:51*/ public class wxtrade {private bigdecimal tradeamout;private string tradeno;private bigdecimal useramout;public bigdecimal getuseramout() {return useramout;}public void setuseramout(bigdecimal useramout) {this.useramout = useramout;}public string gettradeno() {return tradeno;}public void settradeno(string tradeno) {this.tradeno = tradeno;}public bigdecimal gettradeamout() {return tradeamout;}public void settradeamout(bigdecimal tradeamout) {this.tradeamout = tradeamout;} }

扣款策略接口

/*** @author shuliangzhao* @title: deduction* @projectname design-parent* @description: todo* @date 2019/5/28 23:53*/ public interface deduction {public boolean exec(wxblance wxblance,wxtrade wxtrade); }

扣款策略一

/*** @author shuliangzhao* @title: blancededuction* @projectname design-parent* @description: todo* @date 2019/5/28 23:54*/ public class blancededuction implements deduction {@overridepublic boolean exec(wxblance wxblance, wxtrade wxtrade) {if (wxblance.getblance().compareto(wxtrade.gettradeamout()) >= 0) {wxtrade.setuseramout(wxblance.getblance());}return true;} }

扣款策略二

/*** @author shuliangzhao* @title: idcarddeduction* @projectname design-parent* @description: todo* @date 2019/5/28 23:54*/ public class idcarddeduction implements deduction {@overridepublic boolean exec(wxblance wxblance, wxtrade wxtrade) {if (wxblance.getblance().compareto(wxtrade.gettradeamout()) < 0) {wxtrade.setuseramout(wxtrade.gettradeamout());}return true;} }

扣款策略封装

/*** @author shuliangzhao* @title: dedutioncontext* @projectname design-parent* @description: todo* @date 2019/5/28 23:58*/ public class dedutioncontext {private deduction deduction;public dedutioncontext(deduction deduction) {this.deduction = deduction;}public boolean exec(wxblance wxblance,wxtrade wxtrade) {return deduction.exec(wxblance,wxtrade);} }

典型的策略上下文。策略模式的缺陷把所有策略类都暴露出去，怎么修改呢？使用工厂模式根据映射产生策略对象

策略枚举

/*** @author shuliangzhao* @title: strategyenum* @projectname design-parent* @description: todo* @date 2019/5/29 0:00*/ public enum strategyenum {blancededuction("com.sl.factorystrategy.blancededuction"),idcarddeduction("com.sl.factorystrategy.idcarddeduction");string value = "";private strategyenum(string value) {this.value = value;}public string getvalue() {return value;} }

策略工厂

/*** @author shuliangzhao* @title: strategyfactory* @projectname design-parent* @description: todo* @date 2019/5/29 0:03*/ public class strategyfactory {public static deduction getdeduction(strategyenum strategyenum) {deduction deduction = null;try {deduction = (deduction)class.forname(strategyenum.getvalue()).newinstance();} catch (exception e) {e.printstacktrace();}return deduction;} }

扣款调用类

/*** @author shuliangzhao* @title: deductionfacade* @projectname design-parent* @description: todo* @date 2019/5/29 0:06*/ public class deductionfacade {//扣款public static void deduct(wxblance wxblance,wxtrade wxtrade) {strategyenum strate = getstrate(wxblance, wxtrade);deduction deduction = strategyfactory.getdeduction(strate);deduction.exec(wxblance,wxtrade);}//获取扣款策略private static strategyenum getstrate(wxblance wxblance,wxtrade wxtrade) {if (wxblance.getblance().compareto(wxtrade.gettradeamout()) < 0) {return strategyenum.idcarddeduction;}else {return strategyenum.blancededuction;}} }

调用客户端client

/*** @author shuliangzhao* @title: client* @projectname design-parent* @description: todo* @date 2019/5/29 0:10*/ public class client {public static void main(string[] args) {wxtrade wxtrade = new wxtrade();wxtrade.settradeamout(new bigdecimal("1000"));wxblance wxblance = new wxblance();wxblance.setblance(new bigdecimal("999"));deductionfacade.deduct(wxblance,wxtrade);system.out.println(wxtrade.getuseramout());} }

执行结果

 

image.png

小结：
策略模式：负责对扣款封装，保证两个策略自由切换，以后增加策略也很容易

工厂模式：修正策略模式必须对外暴露问题，由工厂模式产生一个具体策略对象

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