笔记8 AOP练习2

场景描述：

　　一张唱片有好多磁道，假设每个磁道只有一首歌，现在需要记录每首歌的播放次数，然后输出。

　　主要业务：歌曲播放

　　辅助功能：记录播放次数（切面）

1.创建唱片接口，CompactDiscs.java

 package soundsystem;

 public interface CompactDiscs {
     void playTrack(int number);
 }

2.创建唱片接口的实现类，BlankDisc.java  里面包含一个方法playTrack(int number)，根据传入的磁道编号，播放对应的歌曲。

 package soundsystem;

 import java.util.List;

 public class BlankDisc implements CompactDiscs {
     private String title;
     private String artist;
     private List<String> tracks;

     public String getTitle() {
         return title;
     }

     public void setTitle(String title) {
         this.title = title;
     }

     public String getArtist() {
         return artist;
     }

     public void setArtist(String artist) {
         this.artist = artist;
     }

     public List<String> getTracks() {
         return tracks;
     }

     public void setTracks(List<String> tracks) {
         this.tracks = tracks;
     }

     @Override
     public void playTrack(int number) {
         System.out.println(tracks.get(number - ));
     }

 }

3.创建记录播放次数的类，TrackCounter.java<切面>

 package soundsystem;

 import java.util.HashMap;
 import java.util.Map;

 import org.aspectj.lang.annotation.Aspect;
 import org.aspectj.lang.annotation.Before;
 import org.aspectj.lang.annotation.Pointcut;

 @Aspect
 public class TrackCounter {
     private Map<Integer, Integer> trackCounts = new HashMap<Integer, Integer>();

     @Pointcut("execution(* soundsystem.CompactDiscs.playTrack(int))" + "&& args(trackNumber)")
     public void trackPlayed(int trackNumber) {
     }

     @Before("trackPlayed(trackNumber)")
     public void countTrack(int trackNumber) {
         int currentCount = getPlayCount(trackNumber);
         trackCounts.put(trackNumber, currentCount + );
     }

     public int getPlayCount(int trackNumber) {
         return trackCounts.containsKey(trackNumber) ? trackCounts.get(trackNumber) : ;
     }
 }

这个切面使用@Pointcut注解定义命名的切点，并使用@Before将一个方法声明为前置通知，切点还声明了要提供给通知方法的参数。

在切点表达式中的args(trackNumber)限定符。它表明传递给playTrack()方法的int类型参数也会传递到通知中去。参数的名称trackNumber也与切点方法签名中的参数相匹 配。这个参数会传递到通知方法中，这个通知方法是通过@Before注解和命名切点trackPlayed(trackNumber)定义的。切点定义中的参数与切点方法中的参数名称是一样的，这样就完成了从命名切点到 通知方法的参数转移。

4.创建配置文件，TrackCounterConfig.java   <声明两个Bean>

 package soundsystem;

 import java.util.ArrayList;
 import java.util.List;

 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.context.annotation.EnableAspectJAutoProxy;

 @Configuration
 @EnableAspectJAutoProxy
 public class TrackCounterConfig {
     @Bean
     public CompactDiscs sgtPeppers() {
         BlankDisc cd = new BlankDisc();
         cd.setTitle("ABCCCCCCCCCCCCCCC");
         cd.setArtist("CCCCCCCCCCCCCCAB");
         List<String> tracks = new ArrayList<String>();
         tracks.add("");
         tracks.add("");
         tracks.add("");
         tracks.add("");
         tracks.add("");
         cd.setTracks(tracks);
         return cd;
     }

     @Bean
     public TrackCounter trackCounter() {
         return new TrackCounter();
     }
 }

5.测试，TrackCounterTest.java

 package soundsystem;

 import org.junit.Test;
 import org.junit.runner.RunWith;
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.test.context.ContextConfiguration;
 import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;

 @RunWith(SpringJUnit4ClassRunner.class)
 @ContextConfiguration(classes = soundsystem.TrackCounterConfig.class)
 public class TrackCounterTest {
     @Autowired
     private CompactDiscs cd;
     @Autowired
     private TrackCounter counter;

     @Test
     public void test() {
         cd.show();
         cd.playTrack();
         cd.playTrack();
         cd.playTrack();
         cd.playTrack();
         cd.playTrack();
         cd.playTrack();
         cd.playTrack();
         cd.playTrack();
         cd.playTrack();
         cd.playTrack();
         cd.playTrack();
         for (int i = ; i < ; i++) {
             System.out.println("磁道" + i + "播放了" + counter.getPlayCount(i) + "次");
         }
     }
 }

6.结果