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Spring AOP常见错误解析
Spring 3.0以后的版本相比于2时代的版本一个重要的变化就是aop所依赖的jar包没有一起发布，需要自己单独下载。
Spring AOP部分使用JDK动态代理或者CGLIB来为目标对象创建代理。如果被代理的目标实现了至少一个接口，则会使用JDK动态代理，如果用JDK动态代理，就必须为被代理的目标实现一个接口（要注意的地方是：需要将ctx.getBean()方法的返回值用接口类型接收）；。所有该目标类型实现的接口都将被代理。若该目标对象没有实现任何接口，则创建一个CGLIB代理，如果使用CGLIB强制代理，就必选事先将CGLIB包导入项目，设置beanNameAutoProxyCreator的proxyTargetClass属性为true。
在编写aop程序时，常见的错误有以下几种：
1.如果提示如下错误：
Exception in thread "main"org.springframework.beans.factory.BeanDefinitionStoreException: Unexpected exception parsing XML document from class path resource[applicationContext.xml]; nested exception is java.lang.NoClassDefFoundError:org/aopalliance/aop/Advice
atorg.springframework.beans.factory.xml.XmlBeanDefinitionReader.doLoadBeanDefinitions(XmlBeanDefinitionReader.java:412)
atorg.springframework.beans.factory.xml.XmlBeanDefinitionReader.loadBeanDefinitions(XmlBeanDefinitionReader.java:334)
atorg.springframework.beans.factory.xml.XmlBeanDefinitionReader.loadBeanDefinitions(XmlBeanDefinitionReader.java:302)
atorg.springframework.beans.factory.support.AbstractBeanDefinitionReader.loadBeanDefinitions(AbstractBeanDefinitionReader.java:174)
atorg.springframework.beans.factory.support.AbstractBeanDefinitionReader.loadBeanDefinitions(AbstractBeanDefinitionReader.java:209)
atorg.springframework.beans.factory.support.AbstractBeanDefinitionReader.loadBeanDefinitions(AbstractBeanDefinitionReader.java:180)
atorg.springframework.beans.factory.support.AbstractBeanDefinitionReader.loadBeanDefinitions(AbstractBeanDefinitionReader.java:243)
atorg.springframework.context.support.AbstractXmlApplicationContext.loadBeanDefinitions(AbstractXmlApplicationContext.java:127)
atorg.springframework.context.support.AbstractXmlApplicationContext.loadBeanDefinitions(AbstractXmlApplicationContext.java:93)
atorg.springframework.context.support.AbstractRefreshableApplicationContext.refreshBeanFactory(AbstractRefreshableApplicationContext.java:131)
atorg.springframework.context.support.AbstractApplicationContext.obtainFreshBeanFactory(AbstractApplicationContext.java:522)
atorg.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:436)
atorg.springframework.context.support.ClassPathXmlApplicationContext.<init>(ClassPathXmlApplicationContext.java:139)
atorg.springframework.context.support.ClassPathXmlApplicationContext.<init>(ClassPathXmlApplicationContext.java:83)
atcom.aoptest.com.Test.main(Test.java:14)
Caused by:java.lang.NoClassDefFoundError: org/aopalliance/aop/Advice
atjava.lang.ClassLoader.defineClass1(Native Method)
atjava.lang.ClassLoader.defineClass(ClassLoader.java:800)
atjava.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
atjava.net.URLClassLoader.defineClass(URLClassLoader.java:449)
atjava.net.URLClassLoader.access$100(URLClassLoader.java:71)
atjava.net.URLClassLoader$1.run(URLClassLoader.java:361)
atjava.net.URLClassLoader$1.run(URLClassLoader.java:355)
atjava.security.AccessController.doPrivileged(NativeMethod)
atjava.net.URLClassLoader.findClass(URLClassLoader.java:354)
atjava.lang.ClassLoader.loadClass(ClassLoader.java:425)
atsun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:308)
atjava.lang.ClassLoader.loadClass(ClassLoader.java:358)
atjava.lang.ClassLoader.defineClass1(Native Method)
atjava.lang.ClassLoader.defineClass(ClassLoader.java:800)
atjava.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
atjava.net.URLClassLoader.defineClass(URLClassLoader.java:449)
atjava.net.URLClassLoader.access$100(URLClassLoader.java:71)
atjava.net.URLClassLoader$1.run(URLClassLoader.java:361)
atjava.net.URLClassLoader$1.run(URLClassLoader.java:355)
atjava.security.AccessController.doPrivileged(NativeMethod)
atjava.net.URLClassLoader.findClass(URLClassLoader.java:354)
atjava.lang.ClassLoader.loadClass(ClassLoader.java:425)
atsun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:308)
atjava.lang.ClassLoader.loadClass(ClassLoader.java:358)
atjava.lang.ClassLoader.defineClass1(Native Method)
atjava.lang.ClassLoader.defineClass(ClassLoader.java:800)
atjava.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
atjava.net.URLClassLoader.defineClass(URLClassLoader.java:449)
atjava.net.URLClassLoader.access$100(URLClassLoader.java:71)
atjava.net.URLClassLoader$1.run(URLClassLoader.java:361)
atjava.net.URLClassLoader$1.run(URLClassLoader.java:355)
atjava.security.AccessController.doPrivileged(NativeMethod)
atjava.net.URLClassLoader.findClass(URLClassLoader.java:354)
atjava.lang.ClassLoader.loadClass(ClassLoader.java:425)
atsun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:308)
atjava.lang.ClassLoader.loadClass(ClassLoader.java:358)
atorg.springframework.aop.config.ConfigBeanDefinitionParser.getAdviceClass(ConfigBeanDefinitionParser.java:410)
atorg.springframework.aop.config.ConfigBeanDefinitionParser.createAdviceDefinition(ConfigBeanDefinitionParser.java:366)
atorg.springframework.aop.config.ConfigBeanDefinitionParser.parseAdvice(ConfigBeanDefinitionParser.java:332)
atorg.springframework.aop.config.ConfigBeanDefinitionParser.parseAspect(ConfigBeanDefinitionParser.java:227)
atorg.springframework.aop.config.ConfigBeanDefinitionParser.parse(ConfigBeanDefinitionParser.java:115)
atorg.springframework.beans.factory.xml.NamespaceHandlerSupport.parse(NamespaceHandlerSupport.java:73)
atorg.springframework.beans.factory.xml.BeanDefinitionParserDelegate.parseCustomElement(BeanDefinitionParserDelegate.java:1419)
atorg.springframework.beans.factory.xml.BeanDefinitionParserDelegate.parseCustomElement(BeanDefinitionParserDelegate.java:1409)
atorg.springframework.beans.factory.xml.DefaultBeanDefinitionDocumentReader.parseBeanDefinitions(DefaultBeanDefinitionDocumentReader.java:184)
atorg.springframework.beans.factory.xml.DefaultBeanDefinitionDocumentReader.doRegisterBeanDefinitions(DefaultBeanDefinitionDocumentReader.java:140)
atorg.springframework.beans.factory.xml.DefaultBeanDefinitionDocumentReader.registerBeanDefinitions(DefaultBeanDefinitionDocumentReader.java:111)
atorg.springframework.beans.factory.xml.XmlBeanDefinitionReader.registerBeanDefinitions(XmlBeanDefinitionReader.java:493)
atorg.springframework.beans.factory.xml.XmlBeanDefinitionReader.doLoadBeanDefinitions(XmlBeanDefinitionReader.java:390)
...14 more
Caused by: java.lang.ClassNotFoundException: org.aopalliance.aop.Advice
atjava.net.URLClassLoader$1.run(URLClassLoader.java:366)
atjava.net.URLClassLoader$1.run(URLClassLoader.java:355)
atjava.security.AccessController.doPrivileged(NativeMethod)
atjava.net.URLClassLoader.findClass(URLClassLoader.java:354)
atjava.lang.ClassLoader.loadClass(ClassLoader.java:425)
atsun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:308)
atjava.lang.ClassLoader.loadClass(ClassLoader.java:358)
...63 more
则说明缺少aop运行所依赖的jar包，需要下载，jar包为
aopalliance-1.0.jar
cglib-nodep-2.2.jar
com.springsource.org.aspectj.tools-1.6.6.RELEASE.jar
com.springsource.org.aspectj.weaver-1.6.8.RELEASE.jar
commons-logging-1.1.3.jar
为了下载方面，我把这几个jar包共享出来，下载地址为：
2.提示以下错误：
Pre-instantiating singletons inorg.springframework.beans.factory.support.DefaultListableBeanFactory@72f08d6f:defining beans [persondaoImpl,transaction,org.springframework.aop.config.internalAutoProxyCreator,org.springframework.aop.aspectj.AspectJPointcutAdvisor#0];root of factory hierarchy
Exception in thread "main"java.lang.ClassCastException:com.sun.proxy.$Proxy0 cannot be cast to com.aoptest.com.PersonDaoImpl
atcom.aoptest.com.Test.main(Test.java:15)
这是由于ctx.getBean()方法的返回值用接口的实现类接收，需要将ctx.getBean()方法的返回值改为用接口类型接收。
Spring AOP常见错误解析