今天学习《Spring实战》第4章《面向切面的Spring》，根据4.3.3小节写出如下切面类：

package proxy;import java.util.HashMap;import java.util.Map;import org.aspectj.lang.ProceedingJoinPoint;import org.aspectj.lang.annotation.AfterReturning;import org.aspectj.lang.annotation.Around;import org.aspectj.lang.annotation.Aspect;import org.aspectj.lang.annotation.Pointcut;import org.springframework.stereotype.Component;@Component@Aspectpublic class Audience {        private Map
    
      trackCounts = new HashMap<>();        @Pointcut("execution(** concert.JayPerform.playTrack(int)) && args(trackNum)")  //<1>    public void track(int trackNum) {}  //<2>        @AfterReturning("track(trackNum)")  //<3>    public void countTrack(int trackNum)    //<4>    {                int currentCount = getPlayCount(trackNum);        trackCounts.put(trackNum, currentCount+1);        System.out.println("------- 这首歌播放了"+(currentCount+1)+"次");    }        public int getPlayCount(int trackNumber)    {        return trackCounts.containsKey(trackNumber)?trackCounts.get(trackNumber):0;    }}
    

代码中 <1>、<2>、<3>、<4> 处，int型参数的名称都是trackNum，这样保证了从命名切点到通知方法的参数转移。并且，这里的参数trackNum与concert.JayPerform.playTrack(int trackNum) 的参数命名相同。

经过实验，发现这4处的参数名称与concert.JayPerform.playTrack(int trackNum)中的参数名称不必相同，只要<1>与<2>处参数名称相同、<3>与<4>处参数名称相同即可。这四处代码可修改如下：

package proxy;import java.util.HashMap;import java.util.Map;import org.aspectj.lang.ProceedingJoinPoint;import org.aspectj.lang.annotation.AfterReturning;import org.aspectj.lang.annotation.Around;import org.aspectj.lang.annotation.Aspect;import org.aspectj.lang.annotation.Pointcut;import org.springframework.stereotype.Component;@Component@Aspectpublic class Audience {        private Map
    
      trackCounts = new HashMap<>();        @Pointcut("execution(** concert.JayPerform.playTrack(int)) && args(num1)")  //<1>    public void track(int num1) {}  //<2>        @AfterReturning("track(val1)")  //<3>    public void countTrack(int val1)    //<4>    {                int currentCount = getPlayCount(val1);        trackCounts.put(val1, currentCount+1);        System.out.println("------- 这首歌播放了"+(currentCount+1)+"次");    }        public int getPlayCount(int trackNumber)    {        return trackCounts.containsKey(trackNumber)?trackCounts.get(trackNumber):0;    }}