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 - 1));
    }

}

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 + 1);
    }

    public int getPlayCount(int trackNumber) {
        return trackCounts.containsKey(trackNumber) ? trackCounts.get(trackNumber) : 0;
    }
}

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("11111");
        tracks.add("222222");
        tracks.add("3333333");
        tracks.add("44444444");
        tracks.add("555555555");
        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(1);
        cd.playTrack(2);
        cd.playTrack(2);
        cd.playTrack(3);
        cd.playTrack(3);
        cd.playTrack(3);
        cd.playTrack(4);
        cd.playTrack(4);
        cd.playTrack(4);
        cd.playTrack(5);
        cd.playTrack(5);
        for (int i = 1; i < 6; i++) {
            System.out.println("磁道" + i + "播放了" + counter.getPlayCount(i) + "次");
        }
    }
}

6.结果