Failed to convert property value of type [$Proxy0 implementing com.s2hs.dao.UserDAO

【转载】http://blog.163.com/liu_zhenxu@yeah/blog/static/6526635320108921247224/

异常信息：

13:47:01,093 ERROR ContextLoader:215 - Context initialization failed
org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'userService' defined in class path resource [applicationContext.xml]: Initialization of bean failed; nested exception is org.springframework.beans.TypeMismatchException: Failed to convert property value of type [$Proxy0 implementing com.s2hs.dao.UserDAO,org.springframework.beans.factory.InitializingBean,org.springframework.aop.SpringProxy,org.springframework.aop.framework.Advised] to required type [com.s2hs.dao.imp.UserDAOImp] for property 'userDao'; nested exception is java.lang.IllegalArgumentException: Cannot convert value of type [$Proxy0 implementing com.s2hs.dao.UserDAO,org.springframework.beans.factory.InitializingBean,org.springframework.aop.SpringProxy,org.springframework.aop.framework.Advised] to required type [com.s2hs.dao.imp.UserDAOImp] for property 'userDao': no matching editors or conversion strategy found
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:480)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory$1.run(AbstractAutowireCapableBeanFactory.java:409)
at java.security.AccessController.doPrivileged(Native Method)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:380)
at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:264)
at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222)
at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:261)
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:185)
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:164)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:429)
at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:728)
at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:380)
at org.springframework.web.context.ContextLoader.createWebApplicationContext(ContextLoader.java:255)
at org.springframework.web.context.ContextLoader.initWebApplicationContext(ContextLoader.java:199)
at org.springframework.web.context.ContextLoaderListener.contextInitialized(ContextLoaderListener.java:45)
at org.apache.catalina.core.StandardContext.listenerStart(StandardContext.java:3934)
at org.apache.catalina.core.StandardContext.start(StandardContext.java:4429)
at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:791)
at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:771)
at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:526)
at org.apache.catalina.startup.HostConfig.deployDirectory(HostConfig.java:987)
at org.apache.catalina.startup.HostConfig.deployDirectories(HostConfig.java:909)
at org.apache.catalina.startup.HostConfig.deployApps(HostConfig.java:495)
at org.apache.catalina.startup.HostConfig.start(HostConfig.java:1206)
at org.apache.catalina.startup.HostConfig.lifecycleEvent(HostConfig.java:314)
at org.apache.catalina.util.LifecycleSupport.fireLifecycleEvent(LifecycleSupport.java:119)
at org.apache.catalina.core.ContainerBase.start(ContainerBase.java:1053)
at org.apache.catalina.core.StandardHost.start(StandardHost.java:722)
at org.apache.catalina.core.ContainerBase.start(ContainerBase.java:1045)
at org.apache.catalina.core.StandardEngine.start(StandardEngine.java:443)
at org.apache.catalina.core.StandardService.start(StandardService.java:516)
at org.apache.catalina.core.StandardServer.start(StandardServer.java:710)
at org.apache.catalina.startup.Catalina.start(Catalina.java:583)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at org.apache.catalina.startup.Bootstrap.start(Bootstrap.java:288)
at org.apache.catalina.startup.Bootstrap.main(Bootstrap.java:413)
Caused by: org.springframework.beans.TypeMismatchException:Failed to convert property value of type [$Proxy0 implementing com.s2hs.dao.UserDAO,org.springframework.beans.factory.InitializingBean,org.springframework.aop.SpringProxy,org.springframework.aop.framework.Advised] to required type [com.s2hs.dao.imp.UserDAOImp] for property 'userDao'; nested exception is java.lang.IllegalArgumentException: Cannot convert value of type [$Proxy0 implementing com.s2hs.dao.UserDAO,org.springframework.beans.factory.InitializingBean,org.springframework.aop.SpringProxy,org.springframework.aop.framework.Advised] to required type [com.s2hs.dao.imp.UserDAOImp] for property 'userDao': no matching editors or conversion strategy found
at org.springframework.beans.BeanWrapperImpl.convertForProperty(BeanWrapperImpl.java:391)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.convertForProperty(AbstractAutowireCapableBeanFactory.java:1289)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.applyPropertyValues(AbstractAutowireCapableBeanFactory.java:1250)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1010)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:472)
... 38 more
Caused by: java.lang.IllegalArgumentException: Cannot convert value of type [$Proxy0 implementing com.s2hs.dao.UserDAO,org.springframework.beans.factory.InitializingBean,org.springframework.aop.SpringProxy,org.springframework.aop.framework.Advised] to required type [com.s2hs.dao.imp.UserDAOImp] for property 'userDao': no matching editors or conversion strategy found
at org.springframework.beans.TypeConverterDelegate.convertIfNecessary(TypeConverterDelegate.java:231)
at org.springframework.beans.TypeConverterDelegate.convertIfNecessary(TypeConverterDelegate.java:138)
at org.springframework.beans.BeanWrapperImpl.convertForProperty(BeanWrapperImpl.java:386)
... 42 more
2010-9-9 13:47:01 org.apache.catalina.core.StandardContext listenerStart

异常信息的大概意思就是不能够创建userService bean ,即spring不能为我们注入userService，所以我在userAction中不能正常使用userService才进行业务操作。

我再三检查了applicationContext.xml文件，发现各种<bean>配置均正确，最终经高人指点，原来是spring默认的注入为接口注入方式。如果我们想用实现类进行注入，需要做两方面的工作：

1、导入CGLIB库，即cglib.jar包

2、在spring配置文件applicationContext.xml中进行一下配置：<aop:aspectj-autoproxy proxy-target-/>

以上两个步骤缺一不可，我就犯在没有写第二步配置代码，添加上就好了。