(接上篇Spring通过切点来选择连接点)
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 [email protected] * @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:
| 注解 | 通知 |
|---|---|
| @After | 通知方法会在目标方法返回或抛出异常后调用 |
| @AfterReturning | 通知方法会在目标方法返回后调用 |
| @AfterThrowing | 通知方法会在目标方法抛出异常后调用 |
| @Around | 通知方法会将目标方法封装起来 |
| @Before | 通知方法会在目标方法调用之前执行 |
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 [email protected] * @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"/>
<!--启用AspectJ自动代理-->
<aop:aspectj-autoproxy/>
<!--声明Audience Bean-->
<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 [email protected] * @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 [email protected] * @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 [email protected] * @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 [email protected] * @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.