SPRING IN ACTION 第4版笔记-第四章ASPECT-ORIENTED SPRING-010-Introduction为类增加新方法

Posted 2020-06-18 shamgod

一、

1.Introduction的作用是给类动态的增加方法

When Spring discovers a bean annotated with @Aspect , it will automatically create a proxy that delegates calls to either the proxied bean or to the introduction implementation, depending on whether the method called belongs to the proxied bean or to the introduced interface.

二、例子

要为演出者增加encore功能

1.

package concert;

public interface Performance {
  void performance();
}

2.

 1 package concert;
 2 
 3 import org.springframework.stereotype.Component;
 4 
 5 @Component
 6 public class Eminem implements Performance{
 7 
 8     @Override
 9     public void performance() {
10         System.out.println("you can do anything set to your mind");
11     }
12 
13 }

3.

package concert;

public interface Encoreable {
    void performEncore();
}

4.

 1 package concert;
 2 
 3 public class DefaultEncoreable implements Encoreable{
 4 
 5     @Override
 6     public void performEncore() {
 7         System.out.println("DefaultEncoreable---> performEncore()");
 8     }
 9 
10 }

5.

 1 package concert;
 2 
 3 import org.aspectj.lang.annotation.Aspect;
 4 import org.aspectj.lang.annotation.DeclareParents;
 5 import org.springframework.stereotype.Component;
 6 
 7 @Aspect
 8 @Component
 9 public class EncoreableIntroducer {
10     @DeclareParents(value = "concert.Performance+", defaultImpl = DefaultEncoreable.class)
11     public static Encoreable encoreable;
12 }

解析：

 @DeclareParents的作用是把"Encoreable"介绍给"Performance",它由三部分组成

(1)value:要增加新功能的bean的接口类型

(2)defaultImpl：要增加的功能接口的实现

(3)增加的功能接口的静态变量

6.配置文件

package concert;

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

@Configuration
@ComponentScan
@EnableAspectJAutoProxy
public class Config {

}

 

7.测试

 1 import org.junit.Test;
 2 import org.junit.runner.RunWith;
 3 import org.springframework.beans.factory.annotation.Autowired;
 4 import org.springframework.context.ApplicationContext;
 5 import org.springframework.test.context.ContextConfiguration;
 6 import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;
 7 
 8 import concert.Config;
 9 import concert.Encoreable;
10 
11 @RunWith(SpringJUnit4ClassRunner.class)
12 @ContextConfiguration(classes=Config.class)
13 public class IntroductionTest {
14   @Autowired
15   ApplicationContext context;
16 
17   @Test
18   public void eddieShouldBeAContestant() {
19     Encoreable eminem = (Encoreable) context.getBean("eminem");
20     eminem.performEncore();
21 //      Performance eminem = (Performance) context.getBean("eminem");
22 //      eminem.performance();
23   }
24 }

 

另外：xml的配置方法：

 1 <?xml version="1.0" encoding="UTF-8"?>
 2 <beans xmlns="http://www.springframework.org/schema/beans"
 3  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
 4  xmlns:aop="http://www.springframework.org/schema/aop"
 5  xsi:schemaLocation="http://www.springframework.org/schema/beans 
 6      http://www.springframework.org/schema/beans/spring-beans.xsd
 7      http://www.springframework.org/schema/aop
 8      http://www.springframework.org/schema/aop/spring-aop.xsd">
 9 
10   <bean id="eddie"
11       class="com.springinaction.springidol.Instrumentalist">
12     <property name="instrument">
13       <bean class="com.springinaction.springidol.Guitar" />
14     </property>
15   </bean>
16 
17   <!--<start id="audience_bean"/>--> 
18   <bean id="audience" 
19       class="com.springinaction.springidol.Audience" />
20   <!--<end id="audience_bean"/>-->
21 
22   <!--<start id="audience_aspect"/>--> 
23   <aop:config>
24     <aop:aspect ref="audience">
25       <aop:pointcut id="performance" expression=
26         "execution(* com.springinaction.springidol.Performer.perform(..))" 
27       /> 
28       <aop:before 
29           pointcut-ref="performance"
30           method="takeSeats()" />
31       <aop:before 
32           pointcut-ref="performance"
33           method="turnOffCellPhones" />
34       <aop:after-returning
35           pointcut-ref="performance"
36           method="applaud" />
37       <aop:after-throwing 
38           pointcut-ref="performance"
39           method="demandRefund" />
40     </aop:aspect>
41     
42     <!--<start id="contestant_introduction"/>--> 
43 <aop:aspect>
44   <aop:declare-parents 
45     types-matching="com.springinaction.springidol.Performer+" 
46     implement-interface="com.springinaction.springidol.Contestant"
47     default-impl="com.springinaction.springidol.GraciousContestant"
48     />
49 </aop:aspect>
50     <!--<end id="contestant_introduction"/>-->
51 
52     <!--
53 <start id="delegate_ref"/>    
54 <aop:declare-parents 
55   types-matching="com.springinaction.springidol.Performer+" 
56   implement-interface="com.springinaction.springidol.Contestant"
57   delegate-ref="contestantDelegate"
58   />
59     <end id="delegate_ref"/>   
60 
61 <start id="contestant_delegate"/>    
62 <bean id="contestantDelegate"
63     class="com.springinaction.springidol.GraciousContestant" />
64     <end id="contestant_delegate"/>   
65 
66      -->
67     
68   </aop:config>
69   <!--<end id="audience_aspect" />-->
70 
71 </beans>

 

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