AOP (面向切面编程)
软件由多个独立的模块组成,但有些功能分布于各个模块之中,比如记日志,这些功能叫做“横切关注点”,cross-cutting concerns。面向切面编程的目的就是——将横切关注点与模块的业务逻辑相分离。
概念
通知,advice
切面要做的事情称作通知。五种类型的通知:before:在方法运行之前。
after:在方法运行之后,无论方法运行是否成功。
after-returning:在方法成功运行之后通知。
after-throwwing:在方法运行期间抛出异常时通知。
around::类似于jsp的Filter,切点的执行由around()方法调用。
切点,pointCut
切点定义了通知发生在何处。
切面,aspect
切面是“通知”和“切点”的结合。
AOP工具
有三大框架——AspectJ、JBossAOP、SpringAOP。通常用AspectJ。
常用类
org.aspectj.lang.
ProceedingJoinPoint
实现around通知的方法的形参。
org.aspectj.lang.ProceedingJoinPoint. proceed()
调用切点方法,类似于jsp的Filter的chain.doFilter(request, response)。
实现around通知的方法的形参。
org.aspectj.lang.ProceedingJoinPoint. proceed()
调用切点方法,类似于jsp的Filter的chain.doFilter(request, response)。
例子
演员表演前观众要入席,表演后观众要鼓掌。
App.java
package com.likeyichu.aop;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class App {
@SuppressWarnings("resource")
public static void main(String[] args)
{
ApplicationContext ctx ;
ctx=new ClassPathXmlApplicationContext("com/likeyichu/aop/beans.xml");
Performer performer=ctx.getBean("performer", Performer.class);
performer.perform();
}
}
/*the audience is taking seats
the performer is performing
clap clap
*/
Performer.java
package com.likeyichu.aop;
public class Performer{
public void perform(){
System.out.println("the performer is performing");
}
}
package com.likeyichu.aop;
public class Audience {
//表演之前要坐下
public void takeSeats(){
System.out.println("the audience is taking seats");
}
//表演成功,故障
public void applause(){
System.out.println("clap clap ");
}
//若表演失败 需要喝倒彩
public void boo(){
System.out.println("boo boo ");
}
}
beans.xml
<?xml version="1.0" encoding="GBK"?>
<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"
xmlns:context="http://www.springframework.org/schema/context"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-4.0.xsd
http://www.springframework.org/schema/context
http://www.springframework.org/schema/context/spring-context-4.0.xsd
http://www.springframework.org/schema/aop
http://www.springframework.org/schema/aop/spring-aop-2.5.xsd" >
<bean id="performer" class="com.likeyichu.aop.Performer"/>
<bean id="audience" class="com.likeyichu.aop.Audience"/>
<aop:config>
<aop:aspect ref="audience">
<aop:pointcut id="performance" expression="execution (* com.likeyichu.aop.Performer.perform(..))"/>
<aop:before pointcut-ref="performance" method="takeSeats"/>
<aop:after-returning pointcut-ref="performance" method="applause"/>
<aop:after-throwing pointcut-ref="performance" method="boo"/>
</aop:aspect>
</aop:config>
</beans>
maven依赖
<dependencies>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-context</artifactId>
<version>4.1.6.RELEASE</version>
</dependency>
<dependency>
<groupId>org.aspectj</groupId>
<artifactId>aspectjweaver</artifactId>
<version>1.6.11</version>
</dependency>
</dependencies>