框架：一个使用spring框架AOP的 例子

首先，你必须对增强(advice)有所了解，增强就是在特定连接点执行的动作。advice contains the logic of your aspect。增强，分为4类：

前增强(before) 在连接点之前调用
后增强(after) 在连接点执行之后调用、
环绕增强(around) 完整控制整个方法流程，必须调用MethodInvocation的proceed促使真实操作发生
异常增强 针对某个异常抛出时调用
书店，一个buyBook业务：

package com.denny_blue.springdemo.aop;

public interface BuyBook {
public void buyBook(String customer,String book)throws NoThisBookException;
}

实现此接口的一个业务对象，如果顾客要买< spring in action>就抛出NoThisBookException异常。

package com.denny_blue.springdemo.aop;

public class MyBuyBook implements BuyBook {
public void buyBook(String customer,String book)throws NoThisBookException{
if(book.equals("< spring in action>"))
throw new NoThisBookException("对不起，没有"+book+"存货了！");
System.out.println(customer+",你好，你已经购买了一本"+book+"!");
}
}

自定义两个异常类，其中NoThisBookException被抛出时将触发MyThrowsAdvice调用：

//NoThisBookException.java

package com.denny_blue.springdemo.aop;

public class NoThisBookException extends RuntimeException {
public NoThisBookException(String msg){
super(msg);
}

}

//BuyBookException.java

package com.denny_blue.springdemo.aop;

public class BuyBookException extends RuntimeException {
public BuyBookException(String msg){
super(msg);
System.out.println(msg);
}

}

OK，接下来就是各类增强了，前增强，在业务方法buyBook之前调用，显示欢迎信息：

package com.denny_blue.springdemo.aop;

import java.lang.reflect.Method;

import org.springframework.aop.MethodBeforeAdvice;

public class MyBeforeAdvice implements MethodBeforeAdvice {

public void before(Method arg0, Object[] arg1, Object target)
throws Throwable {
String customer=(String)arg1[0]; //第2个参数组就是被增强的方法传入的参数，本例中即customer,book
System.out.println("欢迎光临!"+customer+"!"); //显示欢迎信息！，在buyBook方法前调用

}

}

然后是后增强，当顾客已经买了书之后，显示欢送信息：

package com.denny_blue.springdemo.aop;

import java.lang.reflect.Method;

import org.springframework.aop.AfterReturningAdvice;

public class MyAfterAdvice implements AfterReturningAdvice {

public void afterReturning(Object arg0, Method arg1, Object[] arg2,
Object arg3) throws Throwable {
String customer=(String)arg2[0]; //同前增强一样，参数组3为传入参数，具体见spring doc
System.out.println("欢迎下次再来！"+customer+"!"); //显示欢送信息!
}

}

OK，有了上面两个advice我们就能提供给顾客很好的服务态度了，等等？我们还有规则没实现，不是说一名顾客只能买一本书吗？OK，我们用环绕增强来解决，在环绕增强中保存一个HashSet，判断顾客是否来过，来过就抛出一个异常，没来过再放入此Set中：

package com.denny_blue.springdemo.aop;

import java.util.HashSet;
import java.util.Set;

import org.aopalliance.intercept.MethodInterceptor;
import org.aopalliance.intercept.MethodInvocation;

public class MyAroundAdvice implements MethodInterceptor {

private Set customers=new HashSet(); //保存购过书的顾客信息
public Object invoke(MethodInvocation invocation) throws Throwable {
String customer=(String)invocation.getArguments()[0];
if(customers.contains(customer)){
throw new BuyBookException("对不起，一名顾客只能买一本打折书！");
}
Object result=invocation.proceed(); //调用MyBuyBook中的buyBook方法，即真实操作
customers.add(customer);
return result;
}

}

好了，最后一个，异常增强，当顾客要买< spring in action>时，我们的书店没书了，请仓库部门赶快订货！！

package com.denny_blue.springdemo.aop;

import org.springframework.aop.ThrowsAdvice;

public class MyThrowsAdvice implements ThrowsAdvice {
public void afterThrowing(NoThisBookException e){ //可以定义多个方法，只要传入的参数是不同异常
System.out.print("通知仓库，赶紧加订书！");
}

}

好了没？还没，我们需要一个XML文件来组装这些对象，来代理业务接口，完整的beans.xml如下，各元素的含义请自己查看spring reference

?xml version="1.0" encoding="UTF-8"?>
< !DOCTYPE beans PUBLIC "-//SPRING//DTD BEAN//EN" "http://www.springframework.org/dtd/spring-beans.dtd">

< beans>
< bean id="myBuyBookTarget" class="com.denny_blue.springdemo.aop.MyBuyBook"/>
< bean id="myBeforeAdvice" class="com.denny_blue.springdemo.aop.MyBeforeAdvice"/>
< bean id="myAroundAdvice" class="com.denny_blue.springdemo.aop.MyAroundAdvice"/>
< bean id="myAfterAdvice" class="com.denny_blue.springdemo.aop.MyAfterAdvice"/>
< bean id="myThrowsAdvice" class="com.denny_blue.springdemo.aop.MyThrowsAdvice"/>
< bean id="buyBook" class="org.springframework.aop.framework.ProxyFactoryBean">
< property name="proxyInterfaces">
< value>com.denny_blue.springdemo.aop.BuyBook< /value>
< /property>
< property name="interceptorNames">
< list>
< value>myBeforeAdvice< /value>
< value>myAfterAdvice< /value>
< value>myAroundAdvice< /value>
< value>myThrowsAdvice< /value>
< /list>
< /property>
< property name="target">
< ref bean="myBuyBookTarget"/>
< /property>
< /bean>
< /beans>

我们先声明所有的bean，通过

< bean id="myBuyBookTarget" class="com.denny_blue.springdemo.aop.MyBuyBook"/>
确定将要被增强的对象??目标对象(target)，我们可以很容易地替换这个目标对象，只要它实现业务接口。代理的接口通过:

< property name="proxyInterfaces">
< value>com.denny_blue.springdemo.aop.BuyBook< /value>
< /property>
设定，然后是要用到一系列增强，注意，顺序是很有影响的！你可以尝试着改变顺序看看结果：）

< property name="interceptorNames">
< list>
< value>myBeforeAdvice< /value>
< value>myAfterAdvice< /value>
< value>myAroundAdvice< /value>
< value>myThrowsAdvice< /value>
< /list>
< /property>

一切准备好了，我们来测试吧，GO GO GO

package test;

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

import com.denny_blue.springdemo.aop.BuyBook;

public class TestAdvice {
public static void main(String args[]){
ApplicationContext ctx=new FileSystemXmlApplicationContext("/src/beans.xml");

//我的beans.xml放在项目下的src目录，eclipse环境下，请自己调整
BuyBook buybook=(BuyBook)ctx.getBean("buyBook");
buybook.buyBook("jordan","< 深入浅出hibernate>");
// buybook.buyBook("dennis","< spring in action>"); //去掉注释即可观察异常增强
// buybook.buyBook("jordan","< 深入浅出hibernate>"); //去掉注释即可观察环绕增强

}
}