依旧是LogInterceptor的例子。下面是beans.xml:
<?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-2.5.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-2.5.xsd http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-2.5.xsd"> <context:annotation-config /> <context:component-scan base-package="com.bjsxt"/> <aop:aspectj-autoproxy /> </beans>
注意添加aop的namespace和<aop:aspectj-autoproxy />这一句。LogInterceptor的代码如下:
package com.bjsxt.aop; import org.aspectj.lang.ProceedingJoinPoint; import org.aspectj.lang.annotation.Around; import org.aspectj.lang.annotation.Aspect; import org.aspectj.lang.annotation.Before; import org.aspectj.lang.annotation.Pointcut; import org.springframework.stereotype.Component; @Aspect @Component public class LogInterceptor { @Pointcut("execution(public * com.bjsxt.service..*.add(..))") public void myMethod(){}; @Before("myMethod()") public void before() { System.out.println("method before"); } @Around("myMethod()") public void aroundMethod(ProceedingJoinPoint pjp) throws Throwable { System.out.println("method around start"); pjp.proceed(); System.out.println("method around end"); } }
这里需要注意两点:
(1) 这里必须要有@Component,让Spring来new一个LoginInterceptor对象(我们定义了<context:component-scan base-package="com.bjsxt"/>来让Spring来扫描com.bjsxt包;扫描到@Aspect就知道要织入这个类了)。这样才能把LoginInterceptor对象织入UserDAOImpl
(2) execution(public void com.bjsxt.dao.UserDAOImpl.save(com.bjsxt.model.User)"),这是AspectJ语法,execution表示在方法执行时切入。另有其他的切入点,比如属性初始化时、类加载时
根据这个例子,我们来理解一些AOP的概念:
(1) Target: UserDAOImpl是织入的Target
(2) JoinPoint: "execution(public void save())"这里就是JoinPoint,即切入点
(3) Advice: before()方法是Advice,Advice is an action taken by an Aspect at a certain JoinPoint
(4) AdviceType: @Before是AdviceType,表示这是一个Advice that executes before a JoinPoint
(5) PointCut: 从通配符(@Pointcut("execution(public * com.bjsxt.service.*.add(.))"))可以看出,PointCut是JoinPoint的集合,但是注意PointCut必须依赖于一个方法
(6) Aspect: LogInterceptor这个类,或者说LogInterceptor这个类的逻辑(即记录日志)是一个Aspect