• 首先在阐述需求之前对一些名词做点解释：

1. 商户编号：有使用过POS机刷卡的同学，可能都会注意到POS签购单上有一个商户编号，这个编号有15位，前三位代表收单银行，第四位到第七位代表行政区划代码，第八位到第十一位代表商户类型代码及MCC码，最后四位就没什么特殊的了。
2. 手续费：每一笔订单都会产生一笔手续费，从结算给商户的金额中扣取，和刷卡的客户无太多关系，一般按发卡行：收单机构：银联的比例为7：3：1或者8：1：1进行清分。
3. 扣率：费率根据商户的类型（MCC）不同而不同，现在民生类的是0.38%的手续费，一般类是0.78%，餐娱类是1.25%。
4. 订单：订单就是订单啦，应该没人不理解啦。

• 然后描述需求：

现在针对每一笔订单，都会关联到一个商户；每一个商户关联一个固定商户编号；每个商户编号有不同的扣率。比如：1、按每笔收取固定手续费，没交易一笔订 单，收取5角；2、按百分比收取手续费，比如民生类商户按0.38%收取手续费，封顶金额16元；3、按不同交易金额区间收取不同的手续费，比如 0~5000收取每笔订单1元，5000~50000收取每笔订单5角，大于50000收取每笔订单2角；4、不同交易金额区间按不同百分比收取手续费等 等。

• 具体设计不做赘述，直接上类图：

 策略接口StrategyCharge定义了一个计算手续费的方法，有四个实现类StrategyWithCount、StrategyWithCountByStage、StrategyWithRatio和StrategyWithRatioByStage，顾名思义，这四个类分别负责计算1每笔收取固定手续费、2每笔按不同金额区间收取不同手续费、3每笔按固定百分比收取手续费和4每笔按不同金额区间根据不同百分比收取手续的计算。

• 所有类的代码如下：

package src.designpattern.strategy.ex2.model;/*** 扣率实体* * @author wusj* @time 2015年8月10日 上午11:23:06*/
public class DeductionRate {private String id;/*** 资金范围开始值*/private String rangeBottom;/*** 资金范围结束值*/private String rangeTop;/*** 扣率，(0,1)之间表示百分比，大于等于1表示每交易扣款金额(单位为分)*/private String ratio;/*** 最大值*/private String maximum;/*** 最小值*/private String minimum;public String getId() {return id;}public void setId(String id) {this.id = id;}public String getRangeBottom() {return rangeBottom;}public void setRangeBottom(String rangeBottom) {this.rangeBottom = rangeBottom;}public String getRangeTop() {return rangeTop;}public void setRangeTop(String rangeTop) {this.rangeTop = rangeTop;}public String getRatio() {return ratio;}public void setRatio(String ratio) {this.ratio = ratio;}public String getMaximum() {return maximum;}public void setMaximum(String maximum) {this.maximum = maximum;}public String getMinimum() {return minimum;}public void setMinimum(String minimum) {this.minimum = minimum;}}

package src.designpattern.strategy.ex2.model;/*** 扣率和商户编码关联关系** @author wusj* @date 2015年8月10日 上午11:38:34*/
public class DeRateRelateMerCode {private String id;/*** 扣率ID*/private String decutionRateId;/*** 商户编号ID*/private String merchantCodeId;public String getId() {return id;}public void setId(String id) {this.id = id;}public String getDecutionRateId() {return decutionRateId;}public void setDecutionRateId(String decutionRateId) {this.decutionRateId = decutionRateId;}public String getMerchantCodeId() {return merchantCodeId;}public void setMerchantCodeId(String merchantCodeId) {this.merchantCodeId = merchantCodeId;}}

package src.designpattern.strategy.ex2.model;/*** 商户号实体* * @author wusj* @time 2015年8月10日 上午11:23:20*/
public class MerchantCode {private String id;private String merchantName;/*** 扣率类型：*     1每笔收取固定手续费；*     2每笔按不同金额区间收取不同手续费；*  3每笔按固定百分比收取手续费；*     4每笔按不同金额区间根据不同百分比收取手续。*/private String rateType;/*** 手续费计算类*/private String chargeCalClass;private String others;public String getId() {return id;}public void setId(String id) {this.id = id;}public String getMerchantName() {return merchantName;}public void setMerchantName(String merchantName) {this.merchantName = merchantName;}public String getRateType() {return rateType;}public void setRateType(String rateType) {this.rateType = rateType;}public String getChargeCalClass() {return chargeCalClass;}public void setChargeCalClass(String chargeCalClass) {this.chargeCalClass = chargeCalClass;}public String getOthers() {return others;}public void setOthers(String others) {this.others = others;}}

package src.designpattern.strategy.ex2.model;/*** 订单实体** @author wusj* @date 2015年8月10日 上午11:54:43*/
public class Order {private String id;/*** 交易金额（单位分）*/private String amount;/*** 商户编号ID*/private String merchantCodeId;/*** 手续费（单位分）*/private String charge;public String getId() {return id;}public void setId(String id) {this.id = id;}public String getAmount() {return amount;}public void setAmount(String amount) {this.amount = amount;}public String getMerchantCodeId() {return merchantCodeId;}public void setMerchantCodeId(String merchantCodeId) {this.merchantCodeId = merchantCodeId;}public String getCharge() {return charge;}public void setCharge(String charge) {this.charge = charge;}}

package src.designpattern.strategy.ex2.service;import src.designpattern.strategy.ex2.model.Order;/*** 订单接口** @author wusj* @date 2015年8月10日 上午11:57:21*/
public interface OrderService {Order insert(Order order);void update(Order order);void delete(String orderId);void query(String orderId);
}

package src.designpattern.strategy.ex2.service;/*** 策略接口定义** @author wusj* @date 2015年8月10日 上午11:59:55*/
public interface StrategyCharge {/*** 计算手续费* * @param object* @return 返回手续费的字符串形式，单位为分*/String calcullateCharge(Object object);
}

package src.designpattern.strategy.ex2;import src.designpattern.strategy.ex2.service.StrategyCharge;/***** @author wusj* @date 2015年8月10日 上午11:59:24*/
public class ContextCharge {protected StrategyCharge strategyCharge;public String calculateCharge(Object object) {return strategyCharge.calcullateCharge(object);}
}

package src.designpattern.strategy.ex2;import src.designpattern.strategy.ex2.model.Order;
import src.designpattern.strategy.ex2.service.OrderService;
import src.designpattern.strategy.ex2.service.StrategyCharge;/*** 订单接口实现类** @author wusj* @date 2015年8月10日 下午1:19:32*/
public class OrderServiceImpl extends ContextCharge implements OrderService {public OrderServiceImpl(StrategyCharge strategyCharge) {this.strategyCharge = strategyCharge;}public Order insert(Order order) {String charge = this.calculateCharge(order);order.setCharge(charge);System.out.println("insert data");return order;}public void update(Order order) {System.out.println("update data.");}public void delete(String orderId) {System.out.println("delete data.");}public void query(String orderId) {System.out.println("query data.");}}

package src.designpattern.strategy.ex2;import java.util.ArrayList;
import java.util.List;import src.designpattern.strategy.ex2.model.DeductionRate;
import src.designpattern.strategy.ex2.model.Order;
import src.designpattern.strategy.ex2.service.StrategyCharge;/*** 计算每笔收取固定金额手续费的算法** @author wusj* @date 2015年8月10日 下午12:38:48*/
public class StrategyWithCount implements StrategyCharge {public String calcullateCharge(Object object) {// 计算订单的手续费，如果不是订单，抛出异常if (object instanceof Order) {Order order = (Order) object;String merchantCodeId = order.getMerchantCodeId();// 根据merchantCodeId查询DeRateRelateMerCode，再查询DeductionRateList<DeductionRate> rateList = query(merchantCodeId);DeductionRate rate = rateList.get(0);return rate.getRatio();} else {throw new UnsupportedOperationException();}}/*** 模拟查询* * @param merchantCodeId* @return*/private List<DeductionRate> query(String merchantCodeId) {// 需要实现DeductionRate rate = new DeductionRate();rate.setId("123");// 模拟每笔收取0.5元(即50fen)的手续费rate.setRatio("50");List<DeductionRate> list = new ArrayList<DeductionRate>(1);list.add(rate);return list;}
}

package src.designpattern.strategy.ex2;import src.designpattern.strategy.ex2.model.Order;
import src.designpattern.strategy.ex2.service.StrategyCharge;/*** 每笔按不同金额区间收取不同手续费的算法** @author wusj* @date 2015年8月10日 下午12:38:48*/
public class StrategyWithCountByStage implements StrategyCharge {public String calcullateCharge(Object object) {// 计算订单的手续费，如果不是订单，抛出异常if (object instanceof Order) {// 算法return "";} else {throw new UnsupportedOperationException();}}
}

package src.designpattern.strategy.ex2;import java.util.ArrayList;
import java.util.List;import src.designpattern.strategy.ex2.model.DeductionRate;
import src.designpattern.strategy.ex2.model.Order;
import src.designpattern.strategy.ex2.service.StrategyCharge;/*** 计算每笔收取“交易金额*固定百分比”的手续费算法** @author wusj* @date 2015年8月10日 下午12:38:48*/
public class StrategyWithRatio implements StrategyCharge {public String calcullateCharge(Object object) {// 计算订单的手续费，如果不是订单，抛出异常if (object instanceof Order) {Order order = (Order) object;String merchantCodeId = order.getMerchantCodeId();// 根据merchantCodeId查询DeRateRelateMerCode，再查询DeductionRateList<DeductionRate> rateList = query(merchantCodeId);DeductionRate rate = rateList.get(0);String ratio = rate.getRatio();String maximum = rate.getMaximum();String minimum = rate.getMinimum();Float ratioF = Float.parseFloat(ratio);Float maximumF = (maximum == null || "".equals(maximum)) ? -1f: Float.parseFloat(maximum);Float minimumF = (minimum == null || "".equals(minimum)) ? 0f: Float.parseFloat(minimum);Float amountF = Float.parseFloat(order.getAmount());Float chargeF = amountF * ratioF;chargeF = chargeF < minimumF ? minimumF : chargeF;chargeF = (maximumF != -1f && chargeF > maximumF) ? maximumF: chargeF;return String.valueOf(Math.round(chargeF));} else {throw new UnsupportedOperationException();}}/*** 模拟查询* * @param merchantCodeId* @return*/private List<DeductionRate> query(String merchantCodeId) {// 需要实现DeductionRate rate = new DeductionRate();rate.setId("123");// 模拟每笔手续交易金额*0.005，封顶手续费10元(1000分)rate.setRatio("0.005");rate.setMaximum("1000");List<DeductionRate> list = new ArrayList<DeductionRate>(1);list.add(rate);return list;}
}

package src.designpattern.strategy.ex2;import src.designpattern.strategy.ex2.model.Order;
import src.designpattern.strategy.ex2.service.StrategyCharge;/*** 每笔按不同金额区间根据不同百分比收取手续** @author wusj* @date 2015年8月10日 下午12:38:48*/
public class StrategyWithRatioByStage implements StrategyCharge {public String calcullateCharge(Object object) {// 计算订单的手续费，如果不是订单，抛出异常if (object instanceof Order) {// 算法return "";} else {throw new UnsupportedOperationException();}}
}

package src.designpattern.strategy.ex2;import src.designpattern.strategy.ex2.model.MerchantCode;
import src.designpattern.strategy.ex2.model.Order;
import src.designpattern.strategy.ex2.service.OrderService;
import src.designpattern.strategy.ex2.service.StrategyCharge;/*** 测试类** @author wusj* @date 2015年8月10日 下午1:24:23*/
public class MainTest {public static void main(String[] args) {String merchantCodeId = "159";Order order = new Order();order.setAmount("100");order.setId("123");order.setMerchantCodeId(merchantCodeId);try {OrderService orderService = new OrderServiceImpl(getContextCharge(merchantCodeId));Order temp = orderService.insert(order);System.out.println(temp.getCharge());} catch (Exception e) {e.printStackTrace();}}@SuppressWarnings("rawtypes")static StrategyCharge getContextCharge(String merchantCodeId)throws InstantiationException, IllegalAccessException,ClassNotFoundException {MerchantCode code = getMerchantCode(merchantCodeId);String className = code.getChargeCalClass();Class clazz = Class.forName(className);StrategyCharge charge = (StrategyCharge) clazz.newInstance();return charge;}static MerchantCode getMerchantCode(String merchantCodeId) {MerchantCode code = new MerchantCode();code.setId(merchantCodeId);code.setMerchantName("wusj");code.setRateType("1");// 测试每笔固定金额
//      code.setChargeCalClass("src.designpattern.strategy.ex2.StrategyWithCount");// 测试每笔固定比例，且最多可收取的手续费限额code.setChargeCalClass("src.designpattern.strategy.ex2.StrategyWithRatio");code.setOthers("others");return code;}
}