Aspect Oriented Programming 面向切面编程

在Spring中使用这些面向切面相关的注解可以结合使用aspectJ,aspectJ是专门搞动态代理技术的，所以比较专业。

需要在bean.xml中这样写：

<?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>

使用aspectJ需要导入aspectj的jar包 aspectjrt（runtime）和aspectjweave（编织）

如果被代理的类没有实现接口还要导入cglib-nodep的jar包，它可以修改字节码来实现代理。

在代码中的写法：

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//这个注解不能少，这样spring才会将其识别为组件
public class LogInterceptor {
    @Pointcut("execution(public * com.bjsxt.service..*.add(..))")
    public void myMethod(){};//这个method相当于上面定义Pointcut的name，写法比较特殊，但是aspectj就这么搞的。
   
    @Before("myMethod()")//这里的myMethod就相当于Pointcut所指的内容了（"execution(public * com.bjsxt.service..*.add(..))"）。
    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();//表示放行，可以执行其他拦截器，没有就执行方法本身
        System.out.println("method around end");
    }
   
}

附几种Pointcut写法：

package com.xyz.someapp;import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.Pointcut;@Aspect
public class SystemArchitecture {/*** A join point is in the web layer if the method is defined* in a type in the com.xyz.someapp.web package or any sub-package* under that.*/@Pointcut("within(com.xyz.someapp.web..*)")public void inWebLayer() {}/*** A join point is in the service layer if the method is defined* in a type in the com.xyz.someapp.service package or any sub-package* under that.*/@Pointcut("within(com.xyz.someapp.service..*)")public void inServiceLayer() {}/*** A join point is in the data access layer if the method is defined* in a type in the com.xyz.someapp.dao package or any sub-package* under that.*/@Pointcut("within(com.xyz.someapp.dao..*)")public void inDataAccessLayer() {}/*** A business service is the execution of any method defined on a service* interface. This definition assumes that interfaces are placed in the* "service" package, and that implementation types are in sub-packages.** If you group service interfaces by functional area (for example,* in packages com.xyz.someapp.abc.service and com.xyz.def.service) then* the pointcut expression "execution(* com.xyz.someapp..service.*.*(..))"* could be used instead.** Alternatively, you can write the expression using the 'bean'* PCD, like so "bean(*Service)". (This assumes that you have* named your Spring service beans in a consistent fashion.)*/@Pointcut("execution(* com.xyz.someapp.service.*.*(..))")public void businessService() {}/*** A data access operation is the execution of any method defined on a* dao interface. This definition assumes that interfaces are placed in the* "dao" package, and that implementation types are in sub-packages.*/@Pointcut("execution(* com.xyz.someapp.dao.*.*(..))")public void dataAccessOperation() {}}