记一次Spring的aop代理Mybatis的DAO所遇到的问题
2017-08-29 14:44
483 查看
由来
项目中需要实现某个订单的状态改变后然后推送给第三方的功能,由于更改状态的项目和推送的项目不是同一个项目,所以为了不改变原项目的代码,我们考虑用spring的aop来实现。项目用的是springmvc + spring + mybatis 的架构,我们知道spring实现了两种代理方式:JDK动态代理和CGLB动态代理。所以spring对接口和类都可以实现代理。所以只需要考虑在DAO接口的相关update状态的方法上加aop就可以了。整理了下共有六个地方对订单的status做了update。所以配置如下:
<!-- 声明通知类 --> <bean id="aspectBean" class="com.info.web.service.BorrowOrderStatusAspect"></bean> <aop:config> <aop:aspect id="myAspect" ref="aspectBean"> <aop:pointcut expression="execution(public * com.info.risk.dao.IRiskCreditUserDao.updateAssetsSuc(..)) || execution(public * com.info.risk.dao.IRiskCreditUserDao.updateAssetsFail(..)) || execution(public * com.info.web.dao.IBorrowOrderDao.updateByPrimaryKeySelective(..)) || execution(public * com.info.web.dao.IBorrowOrderDao.updateByPrimaryKeyWithBLOBs(..)) || execution(public * com.info.web.dao.IBorrowOrderDao.updateByPrimaryKey(..))" id="servicePointcut" /> <aop:after-returning method="doAfter" pointcut-ref="servicePointcut" /> </aop:aspect> </aop:config>
可是启动项目的时候发现,启动失败,报错信息如下:
……………………………… Caused by: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'repaymentService': Injection of autowired dependencies failed; nested exception is org.springframework.beans.factory.BeanCreationException: Could not autowire field: private com.info.web.dao.IBorrowOrderDao com.info.web.service.RepaymentService.borrowOrderDao; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'IBorrowOrderDao': Post-processing of FactoryBean's singleton object failed; nested exception is org.springframework.aop.framework.AopConfigException: Could not generate CGLIB subclass of class [class com.sun.proxy.$Proxy39]: Common causes of this problem include using a final class or a non-visible class; nested exception is java.lang.IllegalArgumentException: Cannot subclass final class class com.sun.proxy.$Proxy39 at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessPropertyValues(AutowiredAnnotationBeanPostProcessor.java:334) at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1210) at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:537) at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:476) at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:303) at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:230) at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:299) at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:194) at org.springframework.beans.factory.support.DefaultListableBeanFactory.findAutowireCandidates(DefaultListableBeanFactory.java:1120) at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1044) at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:942) at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:533) ... 37 more Caused by: org.springframework.beans.factory.BeanCreationException: Could not autowire field: private com.info.web.dao.IBorrowOrderDao com.info.web.service.RepaymentService.borrowOrderDao; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'IBorrowOrderDao': Post-processing of FactoryBean's singleton object failed; nested exception is org.springframework.aop.framework.AopConfigException: Could not generate CGLIB subclass of class [class com.sun.proxy.$Proxy39]: Common causes of this problem include using a final class or a non-visible class; nested exception is java.lang.IllegalArgumentException: Cannot subclass final class class com.sun.proxy.$Proxy39 at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:561) at org.springframework.beans.factory.annotation.InjectionMetadata.inject(InjectionMetadata.java:88) at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessPropertyValues(AutowiredAnnotationBeanPostProcessor.java:331) ... 48 more Caused by: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'IBorrowOrderDao': Post-processing of FactoryBean's singleton object failed; nested exception is org.springframework.aop.framework.AopConfigException: Could not generate CGLIB subclass of class [class com.sun.proxy.$Proxy39]: Common causes of this problem include using a final class or a non-visible class; nested exception is java.lang.IllegalArgumentException: Cannot subclass final class class com.sun.proxy.$Proxy39 at org.springframework.beans.factory.support.FactoryBeanRegistrySupport.getObjectFromFactoryBean(FactoryBeanRegistrySupport.java:116) at org.springframework.beans.factory.support.AbstractBeanFactory.getObjectForBeanInstance(AbstractBeanFactory.java:1517) at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:251) at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:194) at org.springframework.beans.factory.support.DefaultListableBeanFactory.findAutowireCandidates(DefaultListableBeanFactory.java:1120) at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1044) at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:942) at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:533) ... 50 more Caused by: org.springframework.aop.framework.AopConfigException: Could not generate CGLIB subclass of class [class com.sun.proxy.$Proxy39]: Common causes of this problem include using a final class or a non-visible class; nested exception is java.lang.IllegalArgumentException: Cannot subclass final class class com.sun.proxy.$Proxy39 at org.springframework.aop.framework.CglibAopProxy.getProxy(CglibAopProxy.java:212) at org.springframework.aop.framework.ProxyFactory.getProxy(ProxyFactory.java:109) at org.springframework.aop.framework.autoproxy.AbstractAutoProxyCreator.createProxy(AbstractAutoProxyCreator.java:447) at org.springframework.aop.framework.autoproxy.AbstractAutoProxyCreator.wrapIfNecessary(AbstractAutoProxyCreator.java:333) at org.springframework.aop.framework.autoproxy.AbstractAutoProxyCreator.postProcessAfterInitialization(AbstractAutoProxyCreator.java:293) at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.applyBeanPostProcessorsAfterInitialization(AbstractAutowireCapableBeanFactory.java:422) at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.postProcessObjectFromFactoryBean(AbstractAutowireCapableBeanFactory.java:1719) at org.springframework.beans.factory.support.FactoryBeanRegistrySupport.getObjectFromFactoryBean(FactoryBeanRegistrySupport.java:113) ... 57 more Caused by: java.lang.IllegalArgumentException: Cannot subclass final class class com.sun.proxy.$Proxy39 at org.springframework.cglib.proxy.Enhancer.generateClass(Enhancer.java:446) at org.springframework.cglib.transform.TransformingClassGenerator.generateClass(TransformingClassGenerator.java:33) at org.springframework.cglib.core.DefaultGeneratorStrategy.generate(DefaultGeneratorStrategy.java:25) at org.springframework.cglib.core.AbstractClassGenerator.create(AbstractClassGenerator.java:216) at org.springframework.cglib.proxy.Enhancer.createHelper(Enhancer.java:377) at org.springframework.cglib.proxy.Enhancer.createClass(Enhancer.java:317) at org.springframework.aop.framework.ObjenesisCglibAopProxy.createProxyClassAndInstance(ObjenesisCglibAopProxy.java:57) at org.springframework.aop.framework.CglibAopProxy.getProxy(CglibAopProxy.java:202) ... 64 more
分析原因
从报错信息可以了解说是代理了final修饰的类。可是哪里来的final类? 原来,DAO层使用的是mybatis,可以只写接口不用写实现类。而我们项目中就是没有写实现类。但是spring也可以对接口进行代理,继续分析。Mapper开发规则
在mapper.xml中将namespace设置为mapper.java的全限定名
将mapper.java接口的方法名和mapper.xml中statement的id保持一致。
将mapper.java接口的方法输入参数类型和mapper.xml中statement的parameterType保持一致
将mapper.java接口的方法输出 结果类型和mapper.xml中statement的resultType保持一致。
注意遵循上边四点规范!这样抛弃Dao实现类的写法: 具有更好的可扩展性,提高了灵活度。
先来说明下mybatis为何可以只写接口而不写实现类,通过mybatis源码分析可知:
mybatis通过JDK的动态代理方式,在启动加载配置文件时,根据配置mapper的xml去生成Dao的实现。session.getMapper()使用了代理,当调用一次此方法,都会产生一个代理class的instance,看看这个代理class的实现.
public class MapperProxy implements InvocationHandler { ... public static <T> T newMapperProxy(Class<T> mapperInterface, SqlSession sqlSession) { ClassLoader classLoader = mapperInterface.getClassLoader(); Class<?>[] interfaces = new Class[]{mapperInterface}; MapperProxy proxy = new MapperProxy(sqlSession); return (T) Proxy.newProxyInstance(classLoader, interfaces, proxy); } public Object invoke(Object proxy, Method method, Object[] args) throws Throwable { if (!OBJECT_METHODS.contains(method.getName())) { final Class<?> declaringInterface = findDeclaringInterface(proxy, method); final MapperMethod mapperMethod = new MapperMethod(declaringInterface, method, sqlSession); final Object result = mapperMethod.execute(args); if (result == null && method.getReturnType().isPrimitive()) { throw new BindingException("Mapper method '" + method.getName() + "' (" + method.getDeclaringClass() + ") attempted to return null from a method with a primitive return type (" + method.getReturnType() + ")."); } return result; } return null; }
这里是用到了JDK的代理Proxy。 newMapperProxy()可以取得实现interfaces 的class的代理类的实例。
当执行interfaces中的方法的时候,会自动执行invoke()方法,其中public Object invoke(Object proxy, Method method, Object[] args)中 method参数就代表你要执行的方法.
MapperMethod类会使用method方法的methodName 和declaringInterface去取 sqlMapxml 取得对应的sql,也就是拿declaringInterface的类全名加上 sql-id..
因此,dao类被多次代理,第二次aop进行代理的时候拿到的是第一次代理后的对象,这个对象是个final形式的,因此报错。
解决方法:最后我在外层封装了一个service接口和接口的实现类,将dao注入到该service中,最后对该service实现aop,问题就解决了。
总结
动态代理解决问题的检查点:需要AOP拦截的类是否是final的,final类不可使用CGLIB来代理。
是否在给BEAN配AOP的时候强制使用CGLIB,如果是则可指定proxyTargetClass属性以让spring强制代理目标类。
类是否被多次代理了,如果类被多次代理过,则第二次进行代理的时候拿到的是第一次代理后的对象,这个对象是个final形式的,所以会出现这个错误。
基于第三点要注意,类是否被多次代理不紧紧取决于类是否被配置了多次AOP,如果类实现了某个接口,则还要看类实现的接口是否被aop拦截过。如果类实现了接口且接口也被AOP拦截了,则很可能出现上面的错误(是否出错取决于AOP代理执行的顺序)。
spring配置aop需要注意:
1、proxy-target-class属性值决定是基于接口的还是基于类的代理被创建,启动对@Aspectj的支持 true为cglib(基于类),false为jdk代理(基于接口),不写的话默认为false。为true的话,会导致拦截不了mybatis的mapper
<aop:aspectj-autoproxy proxy-target-class="false" />
2、在类没有实现任何接口,并且没有默认构造函数的情况下,通过构造函数注入时,目前的Spring是无法实现AOP切面拦截的。 参考通过CGLIB实现AOP的浅析(顺便简单对比了一下JDK的动态代理)
相关文章推荐
- mybatis-spring从1.1升级到1.2所带来的dao层级的编写问题
- spring和mybatis整合开发过程中遇到的问题SQLException
- mybatis+spring遇到的一点问题(不定更新)
- mybatis-spring集成:配置多数据库源中遇到的问题
- 在idea里使用SpringBoot整合MyBatis时遇到的Mapper扫描不到的问题
- [原创]java WEB学习笔记104:Spring学习---AOP 前奏,通过一个问题引入动态代理
- Spring+SpringMVC+MyBatis遇到的所有问题汇总
- mybatis遇到的一个问题Result Maps collection already contains value for com.schooldevice.dao.DeviceMapper.
- maven+springmvc+mybatis案例---遇到的2个问题:dataSource、方法找不到
- 搭建springMVC+Mybatis的Maven项目过程中遇到的问题汇总。
- Spring的Dao单元测试及运行遇到的Could not load driverClass ${jdbc.driverClass}问题解决
- Spring与Mybatis的整合过程中遇到的一些问题
- Mybatis和Spring整合(原始Dao)非mapper代理
- 关于MyBatis和Spring整合时,No bean named 'xxx' is defined我遇到的问题
- springMVC+MyBatis+Spring 整合(4) ---解决Spring MVC 对AOP不起作用的问题
- Springmvc+mybatis+Spring整合遇到的问题总结
- springmvc+mybatis+maven项目集成的时候遇到一个问题,项目搭起来以后,http请求怎么都进不到controller中,页面直接返回404错误,控制台没有报任何错误,请大神帮我看看
- spring mvc +mybatis+spring +shrio 项目开发遇到的问题及解决方案。
- Spring + Mybatis - 原始dao开发整合 与 Mapper代理整合
- 整合Spring和mybatis中遇到的问题(java.lang.AbstractMethodError)