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

切面类TraceCount

/**  * 切面类的任务：记录每个磁道被播放的次数  * Created by Administrator on 2017/12/1.  */ @Component @Aspect public class TrackCounter {    private Map<String, Integer> 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

<context:component-scan base-package="aop_test,chapter04"/>  <bean id="compactDisc"   >   <property name="title" value="Sgt. Pepper's Lonely Hearts Club Band" />   <property name="artist" value="The Beatles" />   <property name="tracks">     <list>       <value>Sgt. Pepper's Lonely Hearts Club Band</value>       <value>With a Little Help from My Friends</value>       <value>Lucy in the Sky with Diamonds</value>       <value>Getting Better</value>       <value>Fixing a Hole</value>       <value>She's Leaving Home</value>       <value>Being for the Benefit of Mr. Kite!</value>       <value>Within You Without You</value>       <value>When I'm Sixty-Four</value>       <value>Lovely Rita</value>       <value>Good Morning Good Morning</value>       <value>Sgt. Pepper's Lonely Hearts Club Band (Reprise)</value>       <value>A Day in the Life</value>     </list>   </property> </bean>  <!-- 开启aop注解 --> <aop:aspectj-autoproxy/> 

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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