SPRING IN ACTION 第4版笔记-第四章ASPECT-ORIENTED SPRING-008-带参数的ADVICE

一、

假设有情形如：cd里有很多轨，当播放音乐时，要统计每个音轨的播放次数，这些统计操作不应放在播放方法里，因为统计不是播放音乐的主要职责，这种情况适合应用AOP。

二、

1.

package soundsystem;

public interface CompactDisc {

  void play();
  void playTrack(int trackNumber);
}

2.

 package soundsystem;

 import java.util.List;

 public class BlankDisc implements CompactDisc {

     private String title;
     private String artist;
     private List<String> tracks;

     public BlankDisc() {
         super();
     }

     public BlankDisc(String title, String artist, List<String> tracks) {
         this.title = title;
         this.artist = artist;
         this.tracks = tracks;
     }

     public void play() {
         System.out.println("Playing " + title + " by " + artist);
         for (String track : tracks) {
             System.out.println("-Track: " + track);
         }
     }

     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 trackNumber) {
         System.out.println("playTrack---->" + trackNumber);
     }

 }

3.

 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.CompactDisc.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;
     }
 }

The thing to focus on in the figure is the args(trackNumber) qualifier in the pointcut expression. This indicates that any int argument that is passed into the execution of playTrack() should also be passed into the advice. The parameter name,trackNumber , also matches the parameter in the pointcut method signature.

4.配置文件

 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 CompactDisc cd() {
         BlankDisc cd = new BlankDisc();
         cd.setTitle("Sgt. Pepper's Lonely Hearts Club Band");
         cd.setArtist("The Beatles");
         List<String> tracks = new ArrayList<String>();
         tracks.add("Sgt. Pepper's Lonely Hearts Club Band");
         tracks.add("With a Little Help from My Friends");
         tracks.add("Lucy in the Sky with Diamonds");
         tracks.add("Getting Better");
         tracks.add("Fixing a Hole");
         // ...other tracks omitted for brevity...
         cd.setTracks(tracks);
         return cd;
     }

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

5.或xml作配置文件

 <?xml version="1.0" encoding="UTF-8"?>
 <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:aop="http://www.springframework.org/schema/aop" xsi:schemaLocation="http://www.springframework.org/schema/aop
 http://www.springframework.org/schema/aop/spring-aop.xsd
 http://www.springframework.org/schema/beans
 http://www.springframework.org/schema/beans/spring-beans.xsd">
     <bean id="trackCounter" class="soundsystem.TrackCounter" />
     <bean id="cd" class="soundsystem.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>
                 <!-- ...other tracks omitted for brevity... -->
             </list>
         </property>
     </bean>
     <aop:config>
         <aop:aspect ref="trackCounter">
             <aop:pointcut id="trackPlayed" expression="execution(* soundsystem.CompactDisc.playTrack(int))
 and args(trackNumber)" />
             <aop:before pointcut-ref="trackPlayed" method="countTrack" />
         </aop:aspect>
     </aop:config>
 </beans>

6.测试

 package soundsystem;

 import static org.junit.Assert.assertEquals;

 import org.junit.Rule;
 import org.junit.Test;
 import org.junit.contrib.java.lang.system.StandardOutputStreamLog;
 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 = TrackCounterConfig.class)
 public class TrackCounterTest {
     @Rule
     public final StandardOutputStreamLog log = new StandardOutputStreamLog();
     @Autowired
     private CompactDisc cd;
     @Autowired
     private TrackCounter counter;

     @Test
     public void testTrackCounter() {
         cd.playTrack(1);
         cd.playTrack(2);
         cd.playTrack(3);
         cd.playTrack(3);
         cd.playTrack(3);
         cd.playTrack(3);
         cd.playTrack(7);
         cd.playTrack(7);
         assertEquals(1, counter.getPlayCount(1));
         assertEquals(1, counter.getPlayCount(2));
         assertEquals(4, counter.getPlayCount(3));
         assertEquals(0, counter.getPlayCount(4));
         assertEquals(0, counter.getPlayCount(5));
         assertEquals(0, counter.getPlayCount(6));
         assertEquals(2, counter.getPlayCount(7));
     }
 }