我们在项目中，为了方便及统一管理，经常会用Aop的方式进行日志统一打印，如果这时候你对一个接口实现类进行Aop拦截打印日志，就可能出现org.springframework.beans.factory.BeanNotOfRequiredTypeException的异常

我们先来复现这个异常的出现场景

首先定义一个接口：

package com.xh.spring.aop;

public interface Iface {
    public void say();
}

定义一个接口的实现类：

package com.xh.spring.aop;

import org.springframework.stereotype.Service;

@Service
public class IfaceImpl implements Iface{

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

一个业务处理类，持有接口实现类

package com.xh.spring.aop;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

@Service
public class BusinessService {

    @Autowired
    private IfaceImpl iface;
    
}

关键的代码，通过Aop进行日志打印

package com.xh.spring.aop;

import org.aspectj.lang.ProceedingJoinPoint;
import org.aspectj.lang.annotation.Around;
import org.aspectj.lang.annotation.Aspect;

@Aspect
public class LoggerAspect {
    
    @Around("execution(* com.xh.spring.aop.IfaceImpl.*(..))")
    public void aspectb(ProceedingJoinPoint joinPoint) throws Throwable{
        System.out.println("方法调用前");
        joinPoint.proceed();
        System.out.println("方法调用后");
    }

}

Spring配置文件：

<?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"
        xmlns:tx="http://www.springframework.org/schema/tx"
        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/tx
                http://www.springframework.org/schema/tx/spring-tx-2.5.xsd
                http://www.springframework.org/schema/aop
                http://www.springframework.org/schema/aop/spring-aop-2.5.xsd">
    
    
    <context:component-scan base-package="com.xh.spring.aop">
        <context:include-filter type="annotation" 
                 expression="org.aspectj.lang.annotation.Aspect"/>
    </context:component-scan>
    
    <aop:aspectj-autoproxy/>
    
 </beans>

package com.xh.spring.aop;

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

public class Test {
    public static void main(String[] args) {
        ApplicationContext ctx=new ClassPathXmlApplicationContext("beans.xml");
    }
}

执行结果：

2018-08-29 11:20:32,339 INFO [org.springframework.context.support.ClassPathXmlApplicationContext] - Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@dcf3e99: startup date [Wed Aug 29 11:20:32 CST 2018]; root of context hierarchy
2018-08-29 11:20:32,426 INFO [org.springframework.beans.factory.xml.XmlBeanDefinitionReader] - Loading XML bean definitions from class path resource [beans.xml]
2018-08-29 11:20:33,072 WARN [org.springframework.context.support.ClassPathXmlApplicationContext] - Exception encountered during context initialization - cancelling refresh attempt: org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'businessService': Unsatisfied dependency expressed through field 'iface'; nested exception is org.springframework.beans.factory.BeanNotOfRequiredTypeException: Bean named 'ifaceImpl' is expected to be of type 'com.xh.spring.aop.IfaceImpl' but was actually of type 'com.sun.proxy.$Proxy10'
Exception in thread "main" org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'businessService': Unsatisfied dependency expressed through field 'iface'; nested exception is org.springframework.beans.factory.BeanNotOfRequiredTypeException: Bean named 'ifaceImpl' is expected to be of type 'com.xh.spring.aop.IfaceImpl' but was actually of type 'com.sun.proxy.$Proxy10'
    at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:588)
    at org.springframework.beans.factory.annotation.InjectionMetadata.inject(InjectionMetadata.java:88)
    at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessPropertyValues(AutowiredAnnotationBeanPostProcessor.java:366)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1225)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:552)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:483)
    at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:306)
    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:230)
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:302)
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:197)
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:759)
    at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:866)
    at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:542)
    at org.springframework.context.support.ClassPathXmlApplicationContext.<init>(ClassPathXmlApplicationContext.java:139)
    at org.springframework.context.support.ClassPathXmlApplicationContext.<init>(ClassPathXmlApplicationContext.java:83)
    at com.xh.spring.aop.Test.main(Test.java:8)
Caused by: org.springframework.beans.factory.BeanNotOfRequiredTypeException: Bean named 'ifaceImpl' is expected to be of type 'com.xh.spring.aop.IfaceImpl' but was actually of type 'com.sun.proxy.$Proxy10'
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:378)
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:202)
    at org.springframework.beans.factory.config.DependencyDescriptor.resolveCandidate(DependencyDescriptor.java:207)
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1136)
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:1064)
    at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:585)
    ... 15 more

异常信息的意思大致为，我们需要注入的bean（ifaceImpl）的类型为com.xh.spring.aop.IfaceImpl，而实际的类型为com.sun.proxy.$Proxy10，类型不一致导致的错误。

出现这个异常的原因是Spring Aop默认使用的Jdk动态代理，对com.xh.spring.aop.IfaceImpl生成一个代理类com.sun.proxy.$Proxy10

If the target object to be proxied implements at least one interface then a JDK dynamic proxy will be used. All of the interfaces implemented by the target type will be proxied. If the target object does not implement any interfaces then a CGLIB proxy will be created.
如果要代理的目标对象实现至少一个接口，则将使用JDK动态代理。 目标类型实现的所有接口都将被代理。 如果目标对象未实现任何接口，则将创建CGLIB代理。
以上是Spring AOP官方文档：（更多官方文档参考我的另外一篇博客：面向切面的Spring编程（官方文档翻译））

解决方法：

让Spring强制使用CGLiib生成代理类，修改Spring配置文件，增加proxy-target-class="true"配置

<?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"
        xmlns:tx="http://www.springframework.org/schema/tx"
        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/tx
                http://www.springframework.org/schema/tx/spring-tx-2.5.xsd
                http://www.springframework.org/schema/aop
                http://www.springframework.org/schema/aop/spring-aop-2.5.xsd">
    
    
    <context:component-scan base-package="com.xh.spring.aop">
        <context:include-filter type="annotation" 
                 expression="org.aspectj.lang.annotation.Aspect"/>
    </context:component-scan>
    
    <aop:aspectj-autoproxy proxy-target-class="true"/>
    
 </beans>

proxy-target-class属性的作用
true表示基于类的代理将使用,false表示默认使用Jdk基于接口的代理

我们来看下proxy-target-class标签的实现原理

打开Spring-aop包里，META-INF下的spring.handlers

http\://www.springframework.org/schema/aop=org.springframework.aop.config.AopNamespaceHandler

AopNamespaceHandler就是aop标签的处理类

public class AopNamespaceHandler extends NamespaceHandlerSupport {

    /**
     * Register the {@link BeanDefinitionParser BeanDefinitionParsers} for the
     * '{@code config}', '{@code spring-configured}', '{@code aspectj-autoproxy}'
     * and '{@code scoped-proxy}' tags.
     */
    @Override
    public void init() {
        // In 2.0 XSD as well as in 2.1 XSD.
        registerBeanDefinitionParser("config", new ConfigBeanDefinitionParser());
        registerBeanDefinitionParser("aspectj-autoproxy", new AspectJAutoProxyBeanDefinitionParser());
        registerBeanDefinitionDecorator("scoped-proxy", new ScopedProxyBeanDefinitionDecorator());

        // Only in 2.0 XSD: moved to context namespace as of 2.1
        registerBeanDefinitionParser("spring-configured", new SpringConfiguredBeanDefinitionParser());
    }

}

AspectJAutoProxyBeanDefinitionParser是aspectj-autoproxy标签的解析类，解析aspectj-autoproxy标签的各个属性

class AspectJAutoProxyBeanDefinitionParser implements BeanDefinitionParser {

    @Override
    public BeanDefinition parse(Element element, ParserContext parserContext) {
        AopNamespaceUtils.registerAspectJAnnotationAutoProxyCreatorIfNecessary(parserContext, element);
        extendBeanDefinition(element, parserContext);
        return null;
    }

继续跟踪AopNamespaceUtils.registerAspectJAnnotationAutoProxyCreatorIfNecessary方法

    public static void registerAspectJAutoProxyCreatorIfNecessary(
            ParserContext parserContext, Element sourceElement) {

        BeanDefinition beanDefinition = AopConfigUtils.registerAspectJAutoProxyCreatorIfNecessary(
                parserContext.getRegistry(), parserContext.extractSource(sourceElement));
        useClassProxyingIfNecessary(parserContext.getRegistry(), sourceElement);
        registerComponentIfNecessary(beanDefinition, parserContext);
    }

    public static void registerAspectJAnnotationAutoProxyCreatorIfNecessary(
            ParserContext parserContext, Element sourceElement) {

        BeanDefinition beanDefinition = AopConfigUtils.registerAspectJAnnotationAutoProxyCreatorIfNecessary(
                parserContext.getRegistry(), parserContext.extractSource(sourceElement));
        useClassProxyingIfNecessary(parserContext.getRegistry(), sourceElement);
        registerComponentIfNecessary(beanDefinition, parserContext);
    }

    private static void useClassProxyingIfNecessary(BeanDefinitionRegistry registry, Element sourceElement) {
        if (sourceElement != null) {
- [x]           boolean proxyTargetClass = Boolean.valueOf(sourceElement.getAttribute(PROXY_TARGET_CLASS_ATTRIBUTE));
            if (proxyTargetClass) {
                AopConfigUtils.forceAutoProxyCreatorToUseClassProxying(registry);
            }
            boolean exposeProxy = Boolean.valueOf(sourceElement.getAttribute(EXPOSE_PROXY_ATTRIBUTE));
            if (exposeProxy) {
                AopConfigUtils.forceAutoProxyCreatorToExposeProxy(registry);
            }
        }
    }

重点看下useClassProxyingIfNecessary方法，

    boolean proxyTargetClass = Boolean.valueOf(sourceElement.getAttribute(PROXY_TARGET_CLASS_ATTRIBUTE));
            if (proxyTargetClass) {
                AopConfigUtils.forceAutoProxyCreatorToUseClassProxying(registry);
            }

取出proxy-target-class的属性，如果是true，则使用基于Class的代理

    public static void forceAutoProxyCreatorToUseClassProxying(BeanDefinitionRegistry registry) {
        if (registry.containsBeanDefinition(AUTO_PROXY_CREATOR_BEAN_NAME)) {
            BeanDefinition definition = registry.getBeanDefinition(AUTO_PROXY_CREATOR_BEAN_NAME);
            definition.getPropertyValues().add("proxyTargetClass", Boolean.TRUE);
        }
    }

forceAutoProxyCreatorToUseClassProxying方法会将proxyTargetClass值为true的属性添加到BeanDefinition中，初始化bean的时候，会取出此字段

    public static void forceAutoProxyCreatorToUseClassProxying(BeanDefinitionRegistry registry) {
        if (registry.containsBeanDefinition(AUTO_PROXY_CREATOR_BEAN_NAME)) {
            BeanDefinition definition = registry.getBeanDefinition(AUTO_PROXY_CREATOR_BEAN_NAME);
            definition.getPropertyValues().add("proxyTargetClass", Boolean.TRUE);
        }
    }

打开DefaultAopProxyFactory，createAopProxy方法中，会校验是不是配置了proxyTargetClass为true，如果配置了（config.isProxyTargetClass()）就会使用Cglib来创建代理类（ObjenesisCglibAopProxy(config)）

public class DefaultAopProxyFactory implements AopProxyFactory, Serializable {

@Override
public AopProxy createAopProxy(AdvisedSupport config) throws AopConfigException {
    if (config.isOptimize() || config.isProxyTargetClass() || hasNoUserSuppliedProxyInterfaces(config)) {
        Class<?> targetClass = config.getTargetClass();
        if (targetClass == null) {
            throw new AopConfigException("TargetSource cannot determine target class: " +
                    "Either an interface or a target is required for proxy creation.");
        }
        if (targetClass.isInterface() || Proxy.isProxyClass(targetClass)) {
            return new JdkDynamicAopProxy(config);
        }
        return new ObjenesisCglibAopProxy(config);
    }
    else {
        return new JdkDynamicAopProxy(config);
    }
}