详解spring切面使用传递给被通知方法的参数

本文介绍了详解spring切面使用传递给被通知方法的参数，分享给大家，具体如下：

场景：

BlankDisc代表CD实体，可以通过playTrack()方法直接播放某一个磁道中的歌曲。

需求是记录每个磁道被播放的次数。

一种方法就是修改playTrack()方法，直接在每次调用的时候记录这个数量。但是，记录磁道的播放次数与播放本身是不同的关注点，因此不应该属于playTrack()方法。这应该是切面要完成的任务。

CompactDisc接口

public interface CompactDisc { 
 
  //播放某一个磁道中的歌曲 
  void playTrack(String track); 
 
} 

实现类BlankDisc

public class BlankDisc implements CompactDisc { 
 
  private String title; 
  private String artist; 
  private List tracks; 
 
  public void setTitle(String title) { 
    this.title = title; 
  } 
 
  public void setArtist(String artist) { 
    this.artist = artist; 
  } 
 
  public void setTracks(List tracks) { 
    this.tracks = tracks; 
  } 
 
  @Override 
  public void playTrack(String track) { 
    System.out.println("-Track: " + track); 
  } 
 
} 

切面类TraceCount 

 
@Component 
@Aspect 
public class TrackCounter { 
 
  private Map trackCounts = new HashMap<>(); 
 
  @Pointcut("execution(* chapter04.aop_args.BlankDisc.playTrack(String)) && args(track)") 
  public void trackPlayed(String track) { 
  } 
 
  //在播放前，为该磁道计数 
  @Before("trackPlayed(track)") 
  public void countTrack(String track) { 
    int currentCount = getPlayCount(track); 
    trackCounts.put(track, currentCount + 1); 
  } 
 
  public int getPlayCount(String track) { 
    return trackCounts.containsKey(track) ? trackCounts.get(track) : 0; 
  } 
} 

applicationContext.xml配置文件

 
 
 
   
   
   
     
      Sgt. Pepper's Lonely Hearts Club Band 
      With a Little Help from My Friends 
      Lucy in the Sky with Diamonds 
      Getting Better 
      Fixing a Hole 
      She's Leaving Home 
      Being for the Benefit of Mr. Kite! 
      Within You Without You 
      When I'm Sixty-Four 
      Lovely Rita 
      Good Morning Good Morning 
      Sgt. Pepper's Lonely Hearts Club Band (Reprise) 
      A Day in the Life 
     
   
 
 
 
 

测试

@RunWith(SpringJUnit4ClassRunner.class) 
@ContextConfiguration("classpath:applicationContext.xml") 
public class test_aop_args { 
 
  @Autowired 
  CompactDisc cd; 
 
  @Autowired 
  TrackCounter trackCounter; 
 
  @Test 
  public void test(){ 
    cd.playTrack("Sgt. Pepper's Lonely Hearts Club Band"); 
    cd.playTrack("With a Little Help from My Friends"); 
    cd.playTrack("Lucy in the Sky with Diamonds"); 
    cd.playTrack("Sgt. Pepper's Lonely Hearts Club Band"); 
    cd.playTrack("With a Little Help from My Friends"); 
    cd.playTrack("Sgt. Pepper's Lonely Hearts Club Band"); 
 
    System.out.println(trackCounter.getPlayCount("Sgt. Pepper's Lonely Hearts Club Band")); 
    System.out.println(trackCounter.getPlayCount("With a Little Help from My Friends")); 
    System.out.println(trackCounter.getPlayCount("Lucy in the Sky with Diamonds")); 
    System.out.println(trackCounter.getPlayCount("Getting Better")); 
  } 
} 

测试结果 3，2，1，0

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