《Spring实战》第4章--面向切面的Spring--处理通知中的参数（经验总结）

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
@Aspect
public class Audience {
    
    private Map<Integer, Integer> 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
@Aspect
public class Audience {
    
    private Map<Integer, Integer> 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;
    }

}