演示spring aspectj aop的使用。

首先新建一个maven项目，在项目的pom.xml中添加spring aop相关的依赖项：

如下是完整的pom.xml：

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
	<modelVersion>4.0.0</modelVersion>

	<groupId>cn.outofmemory</groupId>
	<artifactId>spring-aop-aspect</artifactId>
	<version>0.0.1-SNAPSHOT</version>
	<packaging>jar</packaging>

	<name>spring-aop-aspect</name>
	<url>http://maven.apache.org</url>
	<properties>
		<spring.version>3.1.1.RELEASE</spring.version>
	</properties>
	<dependencies>
		<dependency>
			<groupId>org.springframework</groupId>
			<artifactId>spring-core</artifactId>
			<version>${spring.version}</version>
		</dependency>
		<dependency>
			<groupId>org.springframework</groupId>
			<artifactId>spring-context</artifactId>
			<version>${spring.version}</version>
		</dependency>
		<dependency>
			<groupId>org.springframework</groupId>
			<artifactId>spring-aop</artifactId>
			<version>${spring.version}</version>
		</dependency>
		<dependency>
			<groupId>org.aspectj</groupId>
			<artifactId>aspectjrt</artifactId>
			<version>1.6.12</version>
		</dependency>
		<dependency>
			<groupId>org.aspectj</groupId>
			<artifactId>aspectjweaver</artifactId>
			<version>1.6.12</version>
		</dependency>
		<dependency>
			<groupId>cglib</groupId>
			<artifactId>cglib</artifactId>
			<version>2.2</version>
		</dependency>
	</dependencies>
</project>
在maven中我们引入了spring aop相关的依赖，aspectj相关的包有两个，cglib是必须的。

下面我们在项目中新建一个Service类PersonService，它是业务代码，是我们AOP注入的目标类：

package cn.outofmemory.spring_aop_aspect;

import org.springframework.stereotype.Service;

@Service
public class PersonService {

	public void addPerson(String personName) {
		System.out.println("add person " + personName);
	}
	
	public boolean deletePerson(String personName) {
		System.out.println("delete person " + personName) ;
		return true;
	}
	
	public void editPerson(String personName) {
		System.out.println("edit person " + personName);
		throw new RuntimeException("edit person throw exception");
	}
	
}
PersonService类中定义了三个方法，addPerson方法无返回值，而deletePerson方法有返回值，而editPerson方法抛出运行时的异常。

下面我们看Aspect类：

package cn.outofmemory.spring_aop_aspect;

import org.aspectj.lang.JoinPoint;
import org.aspectj.lang.ProceedingJoinPoint;
import org.aspectj.lang.annotation.After;
import org.aspectj.lang.annotation.AfterReturning;
import org.aspectj.lang.annotation.AfterThrowing;
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;

@Component
@Aspect
public class SimpleAspect {
	@Pointcut("execution(* cn.outofmemory.spring_aop_aspect.*Service*.*(..))")
	public void pointCut() {
	}

	@After("pointCut()")
	public void after(JoinPoint joinPoint) {
		System.out.println("after aspect executed");
	}

	@Before("pointCut()")
	public void before(JoinPoint joinPoint) {
		//如果需要这里可以取出参数进行处理
		//Object[] args = joinPoint.getArgs();
		System.out.println("before aspect executing");
	}

	@AfterReturning(pointcut = "pointCut()", returning = "returnVal")
	public void afterReturning(JoinPoint joinPoint, Object returnVal) {
		System.out.println("afterReturning executed, return result is "
				+ returnVal);
	}

	@Around("pointCut()")
	public void around(ProceedingJoinPoint pjp) throws Throwable {
		System.out.println("around start..");
		try {
			pjp.proceed();
		} catch (Throwable ex) {
			System.out.println("error in around");
			throw ex;
		}
		System.out.println("around end");
	}

	@AfterThrowing(pointcut = "pointCut()", throwing = "error")
	public void afterThrowing(JoinPoint jp, Throwable error) {
		System.out.println("error:" + error);
	}
}
SimpleAspect类中的第一个方法是pointCut()方法，此方法无任何执行内容，只有一个@Pointcut的注解，其他方法都会引用这个注解中指定的pointcut表达式。

其他几个方法是各种Advice类型的方法实现，在这些方法中都可以通过JoinPoint实例来获得方法执行的上下文信息，参数信息。需要注意AfterReturning和AfterThrowing，After三种不同Advice的执行顺序。

有了spring框架和aspectj以及cglib的支持，我们只需要实现上面两个类就可以使用spring aop的功能了，下面我们看下如何在spring的配置文件中配置spring aop。

<?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: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-3.0.xsd
                           http://www.springframework.org/schema/aop
                           http://www.springframework.org/schema/aop/spring-aop-3.0.xsd
                           http://www.springframework.org/schema/context
                           http://www.springframework.org/schema/context/spring-context-3.1.xsd">
    <aop:aspectj-autoproxy />
    <context:component-scan base-package="cn.outofmemory" /> 
</beans>
注意在beans节点中需要指定aop命名空间，一家chemaLocation地址，启用aop只需要添加<aop:aspectj-autoproxy/>就可以了。<context:component-scan/>节点用来指定自动扫描bean的命名空间。

最后我们要测试下aop的效果，需要新建一个App类作为程序的入口类。

package cn.outofmemory.spring_aop_aspect;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;


/**
 * Hello world!
 *
 */
public class App 
{
    public static void main( String[] args )
    {
    	ApplicationContext appContext = new ClassPathXmlApplicationContext("/appContext.xml");
    	PersonService personService = appContext.getBean(PersonService.class);
    	String personName = "Jim";
    	personService.addPerson(personName);
    	personService.deletePerson(personName);
    	personService.editPerson(personName);
    	((ClassPathXmlApplicationContext)appContext).close();
    }
}
这个类中我们初始化了ApplicationContext，然后从中得到PersonService的实例，并执行其addPerson,deletePerson,editPerson方法，最后关闭ApplicationContext。

其执行结果如下：

before aspect executing
around start..
add person Jim
after aspect executed
around end
afterReturning executed, return result is null
-------------------------------------
before aspect executing
around start..
delete person Jim
after aspect executed
around end
afterReturning executed, return result is null
----------------------------------------
before aspect executing
around start..
edit person Jim
after aspect executed
error in around
error:java.lang.RuntimeException: edit person throw exception
Exception in thread ...
从上面执行结果可以看到我们要执行的Before，around，after以及around，afterReturning，afterThrowing都正常的执行了。

最后给出此示例项目的完整代码：spring-aop-aspect.zip