为什么为依赖 bean 混合 Spring AOP 代理机制（CGLIB 和 JDKDynmic）不起作用

Question

我在 Spring 应用程序上下文中配置了两个公共类，如下所示：

public class LoadErrorData{
  private ExceptionData exceptionData;
  public LoadErrorData() { } 
  // reminder
}

public class ExceptionData implements Serializable{
  private Resource exceptionDataResource;
  public ExceptionData() { } 
  // reminder
}

Spring applicationContext.xml：

<beans:bean id="loadErrorData" class="com.startup.LoadErrorData" init-method="startup">
  <beans:property name="exceptionData" ref="exceptionData"/> 
</beans:bean>

<beans:bean id="exceptionData" class="com.server.ExceptionData" init-method="startup">
  <beans:property name="exceptionDataResource" value="classpath:${exception.datafile.path}"/>
</beans:bean>

初始化时出现以下异常：

Oct 07, 2013 1:45:21 PM org.apache.catalina.core.StandardContext
listenerStart SEVERE: Exception sending context initialized event to
listener instance of class
org.springframework.web.context.ContextLoaderListener
org.springframework.beans.factory.BeanCreationException: Error
creating bean with name 'loadErrorData' defined in class path resource
[spring/startup-config.xml]: Initialization of bean failed; nested
exception is
org.springframework.beans.ConversionNotSupportedException: Failed to
convert property value of type 'com.sun.proxy.$Proxy12 implementing
java.io.Serializable,org.springframework.aop.SpringProxy,org.springframework.aop.framework.Advised'
to required type 'com.server.IICExceptionData' for property
'exceptionData'; nested exception is java.lang.IllegalStateException:
Cannot convert value of type [com.sun.proxy.$Proxy12 implementing
java.io.Serializable,org.springframework.aop.SpringProxy,org.springframework.aop.framework.Advised]
to required type [com.server.IICExceptionData] for property
'exceptionData': no matching editors or conversion strategy found at
org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:527)
at
org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:456)
at
org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:294)
at
org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:225)
at
org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:291)
at
org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:193)
at
org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:609)
at
org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:918)
at
org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:469)
at
org.springframework.web.context.ContextLoader.configureAndRefreshWebApplicationContext(ContextLoader.java:383)
at
org.springframework.web.context.ContextLoader.initWebApplicationContext(ContextLoader.java:283)
at
org.springframework.web.context.ContextLoaderListener.contextInitialized(ContextLoaderListener.java:111)
at
org.apache.catalina.core.StandardContext.listenerStart(StandardContext.java:4723)
at
org.apache.catalina.core.StandardContext$1.call(StandardContext.java:5226)
at
org.apache.catalina.core.StandardContext$1.call(StandardContext.java:5221)
at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:334)
at java.util.concurrent.FutureTask.run(FutureTask.java:166) at
java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
at
java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
at java.lang.Thread.run(Thread.java:724) Caused by:
org.springframework.beans.ConversionNotSupportedException: Failed to
convert property value of type 'com.sun.proxy.$Proxy12 implementing
java.io.Serializable,org.springframework.aop.SpringProxy,org.springframework.aop.framework.Advised'
to required type 'com.server.IICExceptionData' for property
'exceptionData'; nested exception is java.lang.IllegalStateException:
Cannot convert value of type [com.sun.proxy.$Proxy12 implementing
java.io.Serializable,org.springframework.aop.SpringProxy,org.springframework.aop.framework.Advised]
to required type [com.server.IICExceptionData] for property
'exceptionData': no matching editors or conversion strategy found at
org.springframework.beans.BeanWrapperImpl.convertIfNecessary(BeanWrapperImpl.java:485)
at
org.springframework.beans.BeanWrapperImpl.convertForProperty(BeanWrapperImpl.java:516)
at
org.springframework.beans.BeanWrapperImpl.convertForProperty(BeanWrapperImpl.java:510)
at
org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.convertForProperty(AbstractAutowireCapableBeanFactory.java:1406)
at
org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.applyPropertyValues(AbstractAutowireCapableBeanFactory.java:1365)
at
org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1118)
at
org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:517)
... 19 more Caused by: java.lang.IllegalStateException: Cannot convert
value of type [com.sun.proxy.$Proxy12 implementing
java.io.Serializable,org.springframework.aop.SpringProxy,org.springframework.aop.framework.Advised]
to required type [com.server.IICExceptionData] for property
'exceptionData': no matching editors or conversion strategy found at
org.springframework.beans.TypeConverterDelegate.convertIfNecessary(TypeConverterDelegate.java:241)
at
org.springframework.beans.BeanWrapperImpl.convertIfNecessary(BeanWrapperImpl.java:470)
... 25 more

但是当我把

<aop:scoped-proxy proxy-target-class="true"/>

在ExceptionData bean 配置中或者如果我删除了

implements Serializable

来自ExceptionData

异常消失。我的AOP切入点如下：

expression="execution(* com..*(..))"

似乎 Spring 正在尝试为 bean LoadErrorData 创建 CGLIB 代理 （因为它没有实现任何接口） 并为其依赖项 ExceptionData 创建 JDKdynamicProxy （因为它确实实现了接口 Serializable）。它不能这样做。因为当我告诉 spring 为 ExceptionData 显式创建 CGLIB 代理时，它工作正常。为什么会这样？为什么它不能为一个 bean(ExceptionData) 创建 JDKDynamic Proxy，它是它试图创建 CGLIB 代理的 bean (LoadErrorData) 的依赖项？根据文档，它说 Spring 会自动检测到它。

Answer 1

其实你所描述的情况正是正在发生的事情。

LoadErrorData 将成为 CgLIB 代理（由于没有接口。 ExceptionData 将成为 JDK 动态代理。

但是您的LoadErrorData 需要ExceptionData 类型的bean，JDK 动态代理只是Serializable（因为它只会代理接口而不是类）。永远不可能将其转换为ExceptionData 的实例，因此上下文的加载将失败。 （这也是堆栈跟踪从错误消息中告诉您的内容）。

如果您对所有内容强制使用基于类的代理或删除Serializable 接口，它将起作用。无论哪种方式都会导致基于类的代理。