巧用ThreadLocal实现责任链模式计数器(一)

责任链模式,请参阅:https://www.jianshu.com/p/75946acd80e3
文章中对责任链模式描述相当清楚,也讲述了几种实现方式,使用中当然选择最优的,也就是作者最后提出的优化方案,即参考OkHttp 里面的 Interceptor 实现方案。

此种方式写一个小Demo是没问题的,确实也写了,上代码前先简单说明,Demo逻辑很简单,根据枚举类型StrategyType决定向哪个方向走,原本用if...else或switch就能实现的功能,使用了责任链来模拟处理,几行的代码变成了几十上百行……

  1. 基类(BasePayload、接口与基类)
@Getter
@Builder
public class BasePayload {

    private StrategyType type;
    private Object data;

}
public interface IStrategy {

    /**
     * 处理方法
     *
     * @param payload
     * @param strategy
     */
    void handle(BasePayload payload, IStrategy strategy);

}
@Slf4j
public class BaseStrategy implements IStrategy {

    /**
     * 策略链
     */
    private final List strategies = Lists.newArrayList();

    /**
     * 计数器
     */
    private AtomicInteger index = new AtomicInteger(0);

    /**
     * 注册策略
     *
     * @param strategy
     */
    public BaseStrategy register(IStrategy strategy) {
        strategies.add(strategy);
        return this;
    }

    @Override
    public void handle(BasePayload payload, IStrategy strategy) {
        if (index.intValue() >= strategies.size()) {
            log.warn("无匹配的处理策略,请检查!");
            return;
        }
        // 获取策略后索引++
        IStrategy currStrategy = strategies.get(index.getAndIncrement());
        // 策略处理
        currStrategy.handle(payload, this);
    }

    /**
     * @ClassName BaseStrategy
     * @Description 支持策略类型
     * @Author frinder
     * @Date 2019/9/5 11:53
     * @Verion 1.0
     */
    public enum StrategyType {
        EAST,
        SOUTH,
        WEST,
        NORTH
    }
}
  1. 策略类
public class EastStrategy implements IStrategy {
    @Override
    public void handle(BasePayload payload, IStrategy strategy) {
        if (EAST.equals(payload.getType())) {
            System.out.println("向【北】走10步!");
        } else {
            // 无法处理,交给下一个处理
            strategy.handle(payload, strategy);
        }
    }
}
public class NorthStrategy implements IStrategy {

    @Override
    public void handle(BasePayload payload, IStrategy strategy) {
        if (NORTH.equals(payload.getType())) {
            System.out.println("向【北】走30步!");
        } else {
            // 无法处理,交给下一个处理
            strategy.handle(payload, strategy);
        }
    }

}
public class SouthStrategy implements IStrategy {

    @Override
    public void handle(BasePayload payload, IStrategy strategy) {
        if (SOUTH.equals(payload.getType())) {
            System.out.println("向【南】走5步!");
        } else {
            // 无法处理,交给下一个处理
            strategy.handle(payload, strategy);
        }
    }

}
public class WestStrategy implements IStrategy {

    @Override
    public void handle(BasePayload payload, IStrategy strategy) {
        if (WEST.equals(payload.getType())) {
            System.out.println("向【西】走20步!");
        } else {
            // 无法处理,交给下一个处理
            strategy.handle(payload, strategy);
        }
    }

}
  1. 测试方法
public class App {

    public static void main(String[] args) {
        BaseStrategy strategy = new BaseStrategy();
        strategy.register(new EastStrategy())
                .register(new SouthStrategy())
                .register(new WestStrategy())
                .register(new NorthStrategy());
        strategy.handle(BasePayload.builder()
                        .type(SOUTH)
                        .build(),
                strategy
        );
    }

}

运行结果:

向【南】走5步!
  1. 再次测试
public class App {

    public static void main(String[] args) {
        BaseStrategy strategy = new BaseStrategy();
        strategy.register(new EastStrategy())
                .register(new SouthStrategy())
                .register(new WestStrategy())
                .register(new NorthStrategy());
        strategy.handle(BasePayload.builder()
                        .type(SOUTH)
                        .build(),
                strategy
        );
        strategy.handle(BasePayload.builder()
                        .type(EAST)
                        .build(),
                strategy
        );
    }
}

运行结果

向【南】走5步!
15:40:03.893 [main] WARN com.kiktech.herd.strategy.base.BaseStrategy - EAST 无匹配的处理策略,请检查!

于是,问题出来了
15:40:03.893 [main] WARN com.kiktech.herd.strategy.base.BaseStrategy - EAST 无匹配的处理策略,请检查!
SOUTH正常处理了,EAST却处理不了,但确实有这个策略的,原因呢?对,计数器。

解决方案:

  • 方案一:每次使用策略时,重新实例化;

  • 方案二:每次调用都初始化计数器,保证不遗漏策略;

当然选择方案二了,每次实例化是个比较消耗资源的操作,特别是策略中有连接数据库啊、TCP连接啊之类的,就更加消耗资源了……

责任链不能滥用,否则会出现几行代码就能干的事变成了几十上百行,事倍功半就事与愿违了!!!

--end

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