Spring使用注解创建切面

￡神魔★判官ぃ 2022-05-27 11:43 224阅读 0赞

## **(接上篇[Spring通过切点来选择连接点][Spring])** ##

## **定义切面:** ##

下面将展示Audience类,它定义了一个切面:

package main.java;
    
    import org.aspectj.lang.annotation.*;
    
    /**
     * @author myvina@qq.com
     * @date 18-4-18 上午8:56
     */
    
    @Aspect
    public class Audience {
        @Pointcut("execution(** main.java.Performance.perform(..))")
        public void performance() {}
    
        @Before("performance()")
        public void silenceCellPhones(){
            System.out.println("Silecing cell phones");
        }
    
        @Before("performance()")
        public void takeSeats(){
            System.out.println("Taking seats");
        }
        
        @AfterReturning("performance()")
        public void applause(){
            System.out.println("CLAP CLAP CLAP");
        }
        
        @AfterThrowing("performance()")
        public void demandRefund(){
            System.out.println("Demanding a refund");
        }
    }

Audience类使用了@AspectJ注解进行了标注.该注解表明Audience不仅仅是一个POJO,还是一个切面.

AspectJ提供了五个注解来定义通知:

<table> 
 <tbody> 
  <tr> 
   <th>注解</th> 
   <th>通知</th> 
  </tr> 
 </tbody> 
 <tbody> 
  <tr> 
   <td>@After</td> 
   <td>通知方法会在目标方法返回或抛出异常后调用</td> 
  </tr> 
  <tr> 
   <td>@AfterReturning</td> 
   <td>通知方法会在目标方法返回后调用</td> 
  </tr> 
  <tr> 
   <td>@AfterThrowing</td> 
   <td>通知方法会在目标方法抛出异常后调用</td> 
  </tr> 
  <tr> 
   <td>@Around</td> 
   <td>通知方法会将目标方法封装起来</td> 
  </tr> 
  <tr> 
   <td>@Before</td> 
   <td>通知方法会在目标方法调用之前执行</td> 
  </tr> 
 </tbody> 
</table>

以上注解都要给定一个切点表达式作为它的值

在Audience类中,performance方法使用了@Pointcut注解,为该注解设置的值是一个切点表达式;设置之后,可以用Performance代替冗长的切点表达式.

## **在JavaConfig中设置自动代理:** ##

package main.java;
    
    import org.springframework.context.annotation.Bean;
    import org.springframework.context.annotation.ComponentScan;
    import org.springframework.context.annotation.Configuration;
    import org.springframework.context.annotation.EnableAspectJAutoProxy;
    
    /**
     * @author myvina@qq.com
     * @date 18-4-18 上午9:24
     */
    
    @Configuration
    @EnableAspectJAutoProxy
    public class Config {
        @Bean
        public Audience audience(){
            return new Audience();
        }
    }

在类级别上使用@EnableAspectJProxy注解启用自动代理功能.

## **在XML配置中设置自动代理:** ##

<?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:context="http://www.springframework.org/schema/context"
           xmlns:aop="http://www.springframework.org/schema/aop"
           xsi:schemaLocation="http://www.springframework.org/schema/beans
            http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop.xsd">
    
        <context:component-scan base-package="main.java"/>
    
        
        <aop:aspectj-autoproxy/>
    
        
        <bean id="Audience" class="main.java.Audience"/>
    
    </beans>

不管是JavaConfig还是XML,AspectJ自动代理都会为使用@Aspect注解的Bean创建一个代理,这个代理会围绕着所有该切面的切点所匹配的Bean.这种情况下,将会为main.java bean创建一个代理,Audience类中的通知方法将会在perform()调用前后执行.

## **创建环绕通知: ** ##

package main.java;
    
    import org.aspectj.lang.ProceedingJoinPoint;
    import org.aspectj.lang.annotation.*;
    
    /**
     * @author myvina@qq.com
     * @date 18-4-18 上午8:56
     */
    
    @Aspect
    public class Audience {
        @Pointcut("execution(** main.java.Performance.perform(..))")
        public void performance() {}
    
        @Around("performance()")
        public void watchPerformance(ProceedingJoinPoint joinPoint){
            try{
                System.out.println("Silecing cell phones");
                System.out.println("Taking seats");
                joinPoint.proceed();
                System.out.println("CLAP CLAP CLAP");
            }catch (Throwable e){
                System.out.println("Demanding a refund");
            }
        }
    }

@Around注解表明watchPerformance()方法会做为Performance()切点的环绕通知.该通知达到的效果与上面四个通知达到的效果是一样的.

关于环绕通知,它接受ProceedingJoinPoint作为参数,必须要有这个对象,因为要在通知中通过此参数调用被通知的方法.

如果忘记调用proceed()方法,会阻塞对被通知方法的调用.

## **对以上代码进行测试:** ##

package main.java;
    
    import org.springframework.stereotype.Component;
    
    /**
     * @author myvina@qq.com
     * @date 18-4-18 上午9:48
     */
    
    public class VinaPerform implements Performance {
        @Override
        public void perform() {
            System.out.println("Vina is singing");
        }
    }

创建一个实现类.

package main.java;
    
    import org.springframework.beans.factory.annotation.Autowired;
    import org.springframework.context.annotation.Bean;
    import org.springframework.context.annotation.ComponentScan;
    import org.springframework.context.annotation.Configuration;
    import org.springframework.context.annotation.EnableAspectJAutoProxy;
    
    /**
     * @author myvina@qq.com
     * @date 18-4-18 上午9:24
     */
    
    @Configuration
    @EnableAspectJAutoProxy
    public class Config {
        @Bean
        public VinaPerform vinaPerform(){
            return new VinaPerform();
        }
    
        @Bean
        public Audience audience(){
            return new Audience();
        }
    }

JavaConfig配置文件如上;

package main.java;
    
    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;
    
    /**
     * @author myvina@qq.com
     * @date 18-4-18 上午9:46
     */
    
    @RunWith(SpringJUnit4ClassRunner.class)
    @ContextConfiguration(classes = main.java.Config.class)
    public class Test {
        @Autowired
        private Performance performance;
    
        @org.junit.Test
        public void AudienceTest(){
            performance.perform();
        }
    }

测试代码如上,测试结果为:

四月 18, 2018 10:30:19 上午 org.springframework.test.context.support.DefaultTestContextBootstrapper getDefaultTestExecutionListenerClassNames
    信息: Loaded default TestExecutionListener class names from location [META-INF/spring.factories]: [org.springframework.test.context.web.ServletTestExecutionListener, org.springframework.test.context.support.DirtiesContextBeforeModesTestExecutionListener, org.springframework.test.context.support.DependencyInjectionTestExecutionListener, org.springframework.test.context.support.DirtiesContextTestExecutionListener, org.springframework.test.context.transaction.TransactionalTestExecutionListener, org.springframework.test.context.jdbc.SqlScriptsTestExecutionListener]
    四月 18, 2018 10:30:19 上午 org.springframework.test.context.support.DefaultTestContextBootstrapper getTestExecutionListeners
    信息: Using TestExecutionListeners: [org.springframework.test.context.support.DirtiesContextBeforeModesTestExecutionListener@26ba2a48, org.springframework.test.context.support.DependencyInjectionTestExecutionListener@5f2050f6, org.springframework.test.context.support.DirtiesContextTestExecutionListener@3b81a1bc, org.springframework.test.context.transaction.TransactionalTestExecutionListener@64616ca2, org.springframework.test.context.jdbc.SqlScriptsTestExecutionListener@13fee20c]
    四月 18, 2018 10:30:19 上午 org.springframework.context.support.GenericApplicationContext prepareRefresh
    信息: Refreshing org.springframework.context.support.GenericApplicationContext@2ef5e5e3: startup date [Wed Apr 18 10:30:19 CST 2018]; root of context hierarchy
    Silecing cell phones
    Taking seats
    Vina is singing
    CLAP CLAP CLAP
    
    Process finished with exit code 0

测试结果和预期一样.

[Spring]: https://blog.csdn.net/weixin_41704428/article/details/79983513