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)

   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)

   ...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

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。