AOP的XML配置：配置了两个BeanNameAutoProxyCreator，会怎么样？

在配置Spring AOP时，可以使用

org.springframework.aop.framework.autoproxy.BeanNameAutoProxyCreator

来完成目标服务的拦截。
比如：

<bean id="serviceInteceptorProxyCreator" class="org.springframework.aop.framework.autoproxy.BeanNameAutoProxyCreator">
        <property name="interceptorNames">
            <list>
                <value>helloServiceAOP</value>
            </list>
        </property>
        <property name="beanNames">
            <value>
                helloService
            </value>
        </property>
    </bean>
    <bean id="helloServiceAOP" class="com.bing.aoptest.aop.HelloServiceAOP" />
    <bean id="helloService" class="com.bing.aoptest.service.HelloServiceImpl"></bean>

会在helloService的方法执行之前，先执行helloServiceAOP。
HelloServiceImpl定义如下：

package com.bing.aoptest.service;

public class HelloServiceImpl implements HelloService {

    public void say() {
        System.out.println("Hello");
    }

}

HelloServiceAOP定义如下：

package com.bing.aoptest.aop;

import java.lang.reflect.Method;

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

public class HelloServiceAOP implements MethodInterceptor {

    public Object invoke(MethodInvocation invocation) throws Throwable {
        System.out.println("\nHelloServiceAOP: "
                + invocation.getMethod().getDeclaringClass().getName());
        return invocation.proceed();//放行,调用目标方法
    }

}

那么，如果定义了两个BeanNameAutoProxyCreator会怎么样呢？
xml配置如下：

<?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="helloService" class="com.bing.aoptest.service.HelloServiceImpl"></bean>

    <bean id="serviceInteceptorProxyCreator2" class="org.springframework.aop.framework.autoproxy.BeanNameAutoProxyCreator">
        <property name="interceptorNames">
            <list>
                <value>helloServiceInterceptor</value>
            </list>
        </property>
        <property name="beanNames">
            <value>
                helloService
            </value>
        </property>
    </bean>

    <bean id="serviceInteceptorProxyCreator" class="org.springframework.aop.framework.autoproxy.BeanNameAutoProxyCreator">
        <property name="interceptorNames">
            <list>
                <value>helloServiceAOP</value>
            </list>
        </property>
        <property name="beanNames">
            <value>
                helloService
            </value>
        </property>
    </bean>
    <bean id="helloServiceAOP" class="com.bing.aoptest.aop.HelloServiceAOP" />
    <bean id="helloServiceInterceptor" class="com.bing.aoptest.aop.HelloServiceInterceptor" />
</beans>

helloServiceAOP和helloServiceInterceptor都拦截目标对象，但定义在不同的BeanNameAutoProxyCreator里面。

helloServiceAOP定义如下：

package com.bing.aoptest.aop;

import java.lang.reflect.Method;

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

public class HelloServiceAOP implements MethodInterceptor {

public Object invoke(MethodInvocation invocation) throws Throwable {
    System.out.println("\nHelloServiceAOP: "
            + invocation.getMethod().getDeclaringClass().getName());
    Method m = AOPUtil.getMethod(invocation);
    System.out.println("HelloServiceAOP, method对象:" + m);
    System.out.println("HelloServiceAOP, invocation对象:" + invocation);
    return invocation.proceed();
}

}

helloServiceInterceptor定义如下：

package com.bing.aoptest.aop;

import java.lang.reflect.Method;

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

public class HelloServiceInterceptor implements MethodInterceptor {

    public Object invoke(MethodInvocation invocation) throws Throwable {
        System.out.println("\nHelloServiceInterceptor: "
                + invocation.getMethod().getDeclaringClass().getName());
        Method m = AOPUtil.getMethod(invocation);
        System.out.println("HelloServiceInterceptor, method对象:" + m);

        System.out.println("HelloServiceInterceptor, invocation对象:"
                + invocation);
        return invocation.proceed();
    }

}

调用方法：

package com.bing.aoptest;

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

import com.bing.aoptest.service.HelloService;

/** * Hello world! * */
public class App {
    public static void main(String[] args) {
        ApplicationContext context = new ClassPathXmlApplicationContext(
                "applicationContext.xml");
        HelloService hs = (HelloService) context.getBean("helloService");
        hs.say();

    }
}

输出结果：

HelloServiceAOP: com.bing.aoptest.service.HelloService
HelloServiceAOP, method对象:public final void com.sun.proxy.$Proxy0.say()
HelloServiceAOP, invocation对象:ReflectiveMethodInvocation: public abstract void com.bing.aoptest.service.HelloService.say(); target is of class [com.sun.proxy.$Proxy0]

HelloServiceInterceptor: com.bing.aoptest.service.HelloService
HelloServiceInterceptor, method对象:public void com.bing.aoptest.service.HelloServiceImpl.say()
HelloServiceInterceptor, invocation对象:ReflectiveMethodInvocation: public abstract void com.bing.aoptest.service.HelloService.say(); target is of class [com.bing.aoptest.service.HelloServiceImpl]
Hello

请注意：
HelloServiceAOP, method对象:public final void com.sun.proxy.$Proxy0.say()
HelloServiceInterceptor, method对象:public void com.bing.aoptest.service.HelloServiceImpl.say()

为什么method对象不都是public void com.bing.aoptest.service.HelloServiceImpl.say()呢？

原因
定义了两个org.springframework.aop.framework.autoproxy.BeanNameAutoProxyCreator，按照顺序分别计作A，B，A会为目标对象T生成代理对象P1，B会为P1生成代理对象P2，代理逻辑就变成：
P2代理P1，P1代理T，而不是P2、P1都代理T。

所以，调用T的方法时，应该先执行P1，但P2代理了P1，最终先执行P2，再执行P1，在执行T。

这种情况下，如果T的方法上有注解，只有P1能够拿到注解信息，P2是拿不到的。

所以，不要定义个多个org.springframework.aop.framework.autoproxy.BeanNameAutoProxyCreator的bean。