如何干掉 if else 策略+工厂

2020-06-11 16:03:49来源：博客园阅读 ()

如何干掉 if else 策略+工厂

无论我们做什么业务都无法避免 if else, 但是多重又会导致很多if,今天我们来讲讲如何干掉if else 让你摆脱被if else 支配的恐惧.

　首先让我们来看看简单的if else 语句

public void test(TestUser testUser) {
    if (Objects.isNull(testUser)){
        System.out.println("执行业务 一");
    } else {
        System.out.println("执行业务 二");
    }
}

　　并没有什么问题.但是如果业务稍微复杂一些呢,我们再来看看
　　首先贴出用户实体类

@Data
public class TestUser {
    private Integer id;
    private String name;
    private Viplevel vipLevel;
}

　　在贴出用户VIP枚举

@Getter
@AllArgsConstructor
public enum Viplevel implements Serializable, IEnum {

    NOVIP(0, "普通用户","普通用户"),
    VIP_LEVEL1(1, "包月会员","包月会员"),
    VIP_LEVEL2(2, "季度会员","季度会员"),
    VIP_LEVEL3(3, "半年会员","半年会员"),
    VIP_LEVEL4(4, "年费会员","年费会员");
    
    private final Integer code;

    private final String desc;

    private final String msg;

    @JsonCreator
    public static Viplevel jsonCreator(Integer code) {
        for (Viplevel value : Viplevel.values()) {
            if (value.getCode().equals(code)) {
                return value;
            }
        }
        return null;
    }

    @JsonValue
    public Map getResult() {
        Map<String, Object> map = new LinkedHashMap<String, Object>();
        map.put("code", getCode());
        map.put("desc", getDesc());
        map.put("msg", getMsg());
        return map;
    }
    @Override
    public Serializable getValue() {
        return this.code;
    }
}

　　再来看看业务

public double sellMoney(TestUser testUser) {
    double proPrice = 3000;
    double resultMoney = proPrice;
    if (Objects.isNull(testUser)) {
        //抛出异常
        return proPrice;
    } else {
        if (Viplevel.NOVIP.equals(testUser.getVipLevel())) {
            System.out.println("普通用户");
            resultMoney = proPrice;
        } else if (Viplevel.VIP_LEVEL1.equals(testUser.getVipLevel())) {
            System.out.println("包月会员");
            resultMoney = proPrice - 100;
        } else if (Viplevel.VIP_LEVEL2.equals(testUser.getVipLevel())) {
            System.out.println("季度会员");
            resultMoney = proPrice - 300;
        } else if (Viplevel.VIP_LEVEL3.equals(testUser.getVipLevel())) {
            System.out.println("半年会员:");
            resultMoney = proPrice * 0.8;
        } else if (Viplevel.VIP_LEVEL4.equals(testUser.getVipLevel())) {
            System.out.println("年会员:");
            resultMoney = proPrice * 0.3;
        }
        return resultMoney;
    }
}

　　天哪,这只是一个简单的例子,竟然出现如此多让人懊恼的语句.那么该如何解决呢,别着急,让我们一步步来干掉讨厌的 if else
　　首先思考,最终结果就是要获取到最终产品的售价,那我们就写个计算结果的方法,再让接口去继承他,这样不就能根据需求计算得到结果了吗

/**
 * @author NYY
 * @decription 普通用户最终产品售价
 */
public class NormalStrategy implements ComputeStrategy {
    @Override
    public double compute(double money) {
        return money;
    }
}

/**
 * @author NYY
 * @date 2020/6/4$
 * @decription 月会员最后售价
 */
public class MonthStrategy implements ComputeStrategy {
    @Override
    public double compute(double money) {
        return money - 100;
    }
}

　　....以此类推
　　那么我们最终的业务实现是这样的

private static double getResultMoney(TestUser testUser) {
    double proPrice = 3000;
    double resultMoney = proPrice;
    if (Objects.isNull(testUser)) {
        //抛出异常
        return proPrice;
    } else {
        if (Viplevel.NOVIP.equals(testUser.getVipLevel())) {
            resultMoney = new NormalStrategy().compute(proPrice);
        } else if (Viplevel.VIP_LEVEL1.equals(testUser.getVipLevel())) {
            resultMoney = new MonthStrategy().compute(proPrice);
        }
        //......
    }
    return resultMoney;
}

　　在优化一下变成了这样

private static double getResultMoneyTwo(TestUser testUser) {
    double proPrice = 3000;
    double resultMoney = proPrice;
    ComputeStrategy computeStrategy = null;
    if (Objects.isNull(testUser)) {
        //抛出异常
        return proPrice;
    } else {
        if (Viplevel.NOVIP.equals(testUser.getVipLevel())) {
            computeStrategy = new NormalStrategy();
        } else if (Viplevel.VIP_LEVEL1.equals(testUser.getVipLevel())) {
            computeStrategy = new MonthStrategy();
        }
        //......
        //最后计算结果
        return computeStrategy.compute(proPrice);
    }
}

　　什么,if else 居然还在,我们发现,它需要的不仅是计算结果,主要是根据用户类型,好吧,那我们吧用户类型也提出来

public interface ComputeStrategyTwo {
    // 计算方法
    double compute(double money);
    //获取用户类型
    Integer getUserType();
}

　　接口继承时实现这两个方法

　　新增的 getUserType 方法,主要用来标示该策略的type 值。

/**
 * @author NYY
 * @decription 普通用户
 */
public class NewNormalStrategy implements ComputeStrategyTwo{
    @Override
    public double compute(double money) {
        return money;
    }
    @Override
    public Integer getUserType() {
        return Viplevel.NOVIP.getCode();
    }
}

/**
 * @author NYY
 * @decription 月会员最后售价
 */
public class NewMonthStrategy implements ComputeStrategyTwo {
    @Override
    public double compute(double money) {
        return money - 100;
    }
    @Override
    public Integer getUserType() {
        return Viplevel.VIP_LEVEL1.getCode();
    }
}

　　重点又来了,这时我们就再把策略的工厂加进来

/**
 * @author NYY
 * @decription
 */
public class ComputeStrategyFactory {
    private Map<Integer, ComputeStrategyTwo> map;
    public ComputeStrategyFactory() {

        List<ComputeStrategyTwo> strategies = new ArrayList<>();
        strategies.add(new NewNormalStrategy());//普通用户
        strategies.add(new NewMonthStrategy());//包月用户
        //.......

        // java 8 stream流
        map = strategies.stream().collect(Collectors.toMap(ComputeStrategyTwo::getUserType, computeStrategy -> computeStrategy));
    }

    public static class Possessor {
        public static ComputeStrategyFactory instance = new ComputeStrategyFactory();
    }

    public static ComputeStrategyFactory getInstance() {
        return Possessor.instance;
    }

    public ComputeStrategyTwo get(Integer type) {
        ComputeStrategyTwo computeStrategyTwo = map.get(type);
        return computeStrategyTwo;
    }
}

　　这样我们策略的工厂也有了.最终让我们看看处理业务的代码变成什么样了呢.

private static  double lastResultMoney(TestUser testUser){
    double proPrice = 3000;
    Objects.requireNonNull(testUser,"用户对象为空了");

    ComputeStrategyTwo computeStrategyTwo = ComputeStrategyFactory.getInstance().get(testUser.getVipLevel().getCode());
    if(Objects.isNull(computeStrategyTwo)){
        // throw new GlobalException("用户类型未知");
    //    抛出全局异常
    }
    return computeStrategyTwo.compute(proPrice);
}