JAVA【设计模式】策略模式
一、定义
策略模式:指定义了一系列算法，并将每个算法封装起来，使它们可以相互替换，且算法的变化不会影响使用算法的客户。策略模式属于对象行为模式，它通过对算法进行封装，把使用算法的责任和算法的实现分割开来,并委派给不同的对象对这些算法进行管理。
二、示例：
模拟场景：
1、在本案例中我们模拟在购买商品时候使⽤的各种类型优惠券(满减、直减、折扣、n元购)，这个场景⼏乎也是⼤家的⼀个⽇常购物省钱渠道，购买商品的时候都希望找⼀些优惠券，让购买的商品更加实惠。
传统编码
通过if判断，券的类型越多，if也就越多，代码冗余，臃肿
package com.qf.design.behavior.strategy.tradition;
public class CouponDiscountService {
public double discountAmount(int type, double typeContent, double skuPrice, double typeExt){
//1.直减券
if (type==1){
return skuPrice-typeContent;
}
//2.满减券
if (type==2){
if (skuPrice<typeExt) return skuPrice;
else return skuPrice-typeContent;
}
//3.折扣券
if (type==3){
return skuPrice*typeContent;
}
//4.n元购
if (type==4){
return typeContent;
}
return 0D;
}
}
package com.qf.design.behavior.strategy.tradition;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
public class ApiTest {
private static Logger logger= LoggerFactory.getLogger(ApiTest.class);
public static void main(String[] args) {
CouponDiscountService couponDiscountService=new CouponDiscountService();
//1.直减券
double desc = couponDiscountService.discountAmount(1, 23.5, 55.5, 0);
logger.info("直减券：{}",desc);
//3.折扣券
double discount = couponDiscountService.discountAmount(3, 0.5, 800, 0);
logger.info("折扣券：{}",discount);
}
}
策略模式设计
折扣接口
package com.qf.design.behavior.strategy.design;
import java.math.BigDecimal;
public interface ICouponDiscount<T> {
/**
* 优惠券⾦额计算
* @param couponInfo 券折扣信息；直减、满减、折扣、N元购
* @param skuPrice sku⾦额
* @return 优惠后⾦额
*/
BigDecimal discountAmount(T couponInfo,BigDecimal skuPrice);
}
满减
package com.qf.design.behavior.strategy.design.impl;
import com.qf.design.behavior.strategy.design.ICouponDiscount;
import java.math.BigDecimal;
import java.util.Map;
/**
* 满减
*/
public class MJCouponDiscount implements ICouponDiscount<Map<String,String>> {
@Override
public BigDecimal discountAmount(Map<String, String> couponInfo, BigDecimal skuPrice) {
String x = couponInfo.get("x");
String o = couponInfo.get("n");
// ⼩于商品⾦额条件的，直接返回商品原价
if (skuPrice.compareTo(new BigDecimal(x)) < 0) return skuPrice;
// 减去优惠⾦额判断
BigDecimal discountAmount = skuPrice.subtract(new BigDecimal(0));
if (discountAmount.compareTo(BigDecimal.ZERO) < 1) return
BigDecimal.ONE;
return discountAmount;
}
}
N元购
package com.qf.design.behavior.strategy.design.impl;
import com.qf.design.behavior.strategy.design.ICouponDiscount;
import java.math.BigDecimal;
public class NYGCouponDiscount implements ICouponDiscount<Double> {
@Override
public BigDecimal discountAmount(Double couponInfo, BigDecimal skuPrice) {
return new BigDecimal(couponInfo);
}
}
直减价
package com.qf.design.behavior.strategy.design.impl;
import com.qf.design.behavior.strategy.design.ICouponDiscount;
import java.math.BigDecimal;
public class ZJCouponDiscount implements ICouponDiscount<Double> {
@Override
public BigDecimal discountAmount(Double couponInfo, BigDecimal skuPrice) {
BigDecimal discountAmount = skuPrice.subtract(new
BigDecimal(couponInfo));
if (discountAmount.compareTo(BigDecimal.ZERO) < 1) return
BigDecimal.ONE;
return discountAmount;
}
}
折扣价
package com.qf.design.behavior.strategy.design.impl;
import com.qf.design.behavior.strategy.design.ICouponDiscount;
import java.math.BigDecimal;
public class ZKCouponDiscount implements ICouponDiscount<Double> {
@Override
public BigDecimal discountAmount(Double couponInfo, BigDecimal skuPrice) {
BigDecimal discountAmount = skuPrice.multiply(new
BigDecimal(couponInfo)).setScale(2, BigDecimal.ROUND_HALF_UP);
if (discountAmount.compareTo(BigDecimal.ZERO) < 1) return
BigDecimal.ONE;
return discountAmount;
}
}
策略控制类
package com.qf.design.behavior.strategy.design;
import java.math.BigDecimal;
public class Context<T> {
private ICouponDiscount<T> iCouponDiscount;
public Context(ICouponDiscount<T> iCouponDiscoun){
this.iCouponDiscount=iCouponDiscoun;
}
public BigDecimal discountAmount(T couponInfo,BigDecimal skuPrice){
return iCouponDiscount.discountAmount(couponInfo,skuPrice);
}
}
测试：ApiTest
package com.qf.design.behavior.strategy.design;
import com.qf.design.behavior.strategy.design.impl.MJCouponDiscount;
import com.qf.design.behavior.strategy.design.impl.NYGCouponDiscount;
import com.qf.design.behavior.strategy.design.impl.ZJCouponDiscount;
import com.qf.design.behavior.strategy.design.impl.ZKCouponDiscount;
import org.junit.Test;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import java.math.BigDecimal;
import java.util.HashMap;
import java.util.Map;
public class ApiTest {
private Logger logger= LoggerFactory.getLogger(ApiTest.class);
@Test
public void test_zj(){
Context<Double> doubleContext = new Context<>(new ZJCouponDiscount());
BigDecimal bigDecimal = doubleContext.discountAmount(12.3, new BigDecimal(56.3));
logger.info("直减后的价格：{}",bigDecimal);
}
@Test
public void test_zk(){
Context<Double> doubleContext = new Context<>(new ZKCouponDiscount());
BigDecimal bigDecimal = doubleContext.discountAmount(0.5, new BigDecimal(56.3));
logger.info("折扣后的价格：{}",bigDecimal);
}
@Test
public void test_mj(){
Context<Map<String, String>> doubleContext = new Context<Map<String, String>>(new MJCouponDiscount());
HashMap<String, String> hashMap = new HashMap<>();
hashMap.put("x","100");
hashMap.put("0","10");
BigDecimal bigDecimal = doubleContext.discountAmount(hashMap, new BigDecimal(100));
logger.info("满减后的价格：{}",bigDecimal);
}
@Test
public void test_nyg(){
Context<Double> doubleContext = new Context<>(new NYGCouponDiscount());
BigDecimal bigDecimal = doubleContext.discountAmount(60.3, new BigDecimal(56.3));
logger.info("一元购后的价格：{}",bigDecimal);
}
}
UML关系图
总结：
以上的策略模式案例相对来说不并不复杂，主要的逻辑都是体现在关于不同种类优惠券的计算折扣策略上。结构相对来说也⽐较简单，在实际的开发中这样的设计模式也是⾮常常⽤的。另外这样的设计与命令模式、适配器模式结构相似，但是思路是有差异的。
通过策略设计模式的使⽤可以把我们⽅法中的if语句优化掉，⼤量的if语句使⽤会让代码难以扩展，也不好维护，同时在后期遇到各种问题也很难维护。在使⽤这样的设计模式后可以很好的满⾜隔离性与和扩展性，对于不断新增的需求也⾮常⽅便承接。
