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.
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😏!
4. 代码
Tips
- 欢迎收藏和转发，感谢你的支持！(๑•̀ㅂ•́)و✧
- 欢迎关注我的公众号：庄里程序猿，读书笔记教程资源第一时间获得！
