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"
   class="chapter04.aop_args.BlankDisc">
  <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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