还在用if else？策略模式了解一下！

在公司负责的就是订单取消业务，老系统中各种类型订单取消都是通过if else 判断不同的订单类型进行不同的逻辑。在经历老系统的折磨和产品需求的不断变更，决定进行一次大的重构：消灭 if else。

接下来就向大家介绍下是如何消灭 if else。

1. if else模式

@service
public class cancelorderservice {

    public void process(orderdto orderdto) {
        int servicetype = orderdto.getservicetype();
        if (1 == servicetype) {
            system.out.println("取消即时订单");
        } else if (2 == servicetype) {
            system.out.println("取消预约订单");
        } else if (3 == servicetype) {
            system.out.println("取消拼车订单");
        }
    }
}

若干个月再来看就是这样的感觉

2. 策略模式

2.1 策略模式实现的service

@service
public class cancelorderstrategyservice {

    @autowired
    private strategycontext context;

    public void process(orderdto orderdto) {
        ordertypeenum ordertypeenum = ordertypeenum.getbycode(orderdto.getservicetype());
        abstractstrategy strategy = context.getstrategy(ordertypeenum);
        strategy.process(orderdto);
    }
}

简洁的有点过分了是不是!!!

2.2 各种类型策略实现及抽象策略类

下面选取了即时订单和预约订单的策略.

@service
@ordertypeannotation(ordertype = ordertypeenum.instant)
public class instantorderstrategy extends abstractstrategy {
    @override
    public void process(orderdto orderdto) {
        system.out.println("取消即时订单");
    }
}

@service
@ordertypeannotation(ordertype = ordertypeenum.booking)
public class bookingorderstrategy extends abstractstrategy {
    @override
    public void process(orderdto orderdto) {
        system.out.println("取消预约订单");
    }
}

public abstract class abstractstrategy {
    abstract public void process(orderdto orderdto);
}

2.3 策略类型注解

每个策略中增加了注解ordertypeannotation,以标注适用于不同类型的策略内容.

@target({elementtype.type})
@retention(retentionpolicy.runtime)
@documented
@inherited
public @interface ordertypeannotation {
    ordertypeenum ordertype();
}

2.4 策略处理器类strategyprocessor和策略上下文strategycontext

其中最为核心的为strategyprocessor 策略处理器类和strategycontext 策略上下文,

@component
public class strategyprocessor implements beanfactorypostprocessor {

    private static final string strategy_package = "com.lujiahao.strategy";

    @override
    public void postprocessbeanfactory(configurablelistablebeanfactory configurablelistablebeanfactory) throws beansexception {
        map<ordertypeenum, class> handlermap = maps.newhashmapwithexpectedsize(3);
        classscanner.scan(strategy_package, ordertypeannotation.class).foreach(clazz -> {
            ordertypeenum type = clazz.getannotation(ordertypeannotation.class).ordertype();
            handlermap.put(type, clazz);
        });

        strategycontext context = new strategycontext(handlermap);
        configurablelistablebeanfactory.registersingleton(strategycontext.class.getname(), context);
    }
}

public class strategycontext {
    private map<ordertypeenum, class> strategymap;

    public strategycontext(map<ordertypeenum, class> strategymap) {
        this.strategymap = strategymap;
    }

    public abstractstrategy getstrategy(ordertypeenum ordertypeenum) {
        if (ordertypeenum == null) {
            throw new illegalargumentexception("not fond enum");
        }

        if (collectionutils.isempty(strategymap)) {
            throw new illegalargumentexception("strategy map is empty,please check you strategy package path");
        }

        class clazz = strategymap.get(ordertypeenum);
        if (clazz == null) {
            throw new illegalargumentexception("not fond strategy for type:" + ordertypeenum.getcode());
        }

        return (abstractstrategy) springbeanutils.getbean(clazz);
    }
}

• 首先会扫描指定包中标有@ordertypeannotation的类
• 将符合类的对应的枚举值作为key，对应的类作为value，保存在策略map中
• 初始化strategycontext,并注册到spring容器中,同时将策略map传入其中

我们使用了枚举作为map中的key,相信大家很少有人这样操作过,不过可以放心操作.通过下面两篇文章解答大家的疑问.

• 自定义枚举类 enum 是否可以作为 hashmap 的key
• java 在 map 中使用复杂数据类型作为 key

3. 总结

策略模式极大的减少if else等模板代码,在提升代码可读性的同时,也大大增加代码的灵活性,添加新的策略即可以满足业务需求.
本人在我司业务中对策略模式的应用得到了很好的验证,从此再也不用担心产品改需求.
用策略模式一时爽,一直用一直爽