設計模式-策略模式和工廠模式結合使用

• 怎么把策略模式和工廠模式結合起來使用

如果大家對策略模式和工廠模式不是很了解的話可以先看前面文章
策略模式：https://www.jianshu.com/p/958281936901
工廠模式：https://www.jianshu.com/p/9078481e00c6

大家可能都用過微信支付，在使用微信支付付錢時候：

1、當我們的付款金額大於我們的余額時，會讓我們使用銀行卡支付，
2、余額充足的時候會讓我們優先使用余額里面的錢
扣款策略一：
余額(blance) >= 付款金額(tradeAmout) 使用余額
扣款策略二：
余額(blance) < 付款金額(tradeAmout) 使用銀行卡
很明顯這是一個策略模式的實際應用，但是你還記得策略模式的缺陷嗎？它的具體策略必須暴露出去，而且還要由上層模塊初始化，這不適合，與迪米特法則不符( 迪米特法則（Law of Demeter）又叫作最少知識原則（Least Knowledge Principle 簡寫LKP），就是說一個對象應當對其他對象有盡可能少的了解,不和陌生人說話。注：摘自百度百科，這個迪米特法則下次再細講)沖突。高層模塊對底層模塊僅僅在接觸層次上，而不應該是耦合關系。問題出了，我們應該想辦法解決，正好工廠模式可以幫我們解決這個問題。但是引入工廠模式也有問題，工廠方法要指定一個類，它才能生產對象，我們用枚舉來完成。
首先我們先建兩個實體類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 { //余額 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 { @Override public 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 { @Override public boolean exec(WxBlance wxBlance, WxTrade wxTrade) { if (wxBlance.getBlance().compareTo(wxTrade.getTradeAmout()) < 0) { wxTrade.setUserAmout(wxTrade.getTradeAmout()); } return true; } } 

扣款策略封裝

/** * @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類都暴露出去，怎么修改呢？使用工廠模式根據映射產生策略對象

策略枚舉

/** * @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; } } 

策略工廠

/** * @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; } } 

扣款調用類

/** * @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); } //獲取扣款策略 private static StrategyEnum getStrate(WxBlance wxBlance,WxTrade wxTrade) { if (wxBlance.getBlance().compareTo(wxTrade.getTradeAmout()) < 0) { return StrategyEnum.IdCardDeduction; }else { return StrategyEnum.BlanceDeduction; } } } 

調用客戶端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()); } } 

執行結果

 

 

小結：
策略模式：負責對扣款封裝，保證兩個策略自由切換，以后增加策略也很容易

工廠模式：修正策略模式必須對外暴露問題，由工廠模式產生一個具體策略對象