org.springframework.aop.framework.AopConfigException: Could not generate CGLIB subclass of class [c

Exception in thread "main" org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'forumService': FactoryBean threw
exception on object creation; nested exception is org.springframework.aop.framework.AopConfigException: Could not generate CGLIB subclass of class
[class java.lang.String]: 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 java.lang.String
at org.springframework.beans.factory.support.FactoryBeanRegistrySupport.doGetObjectFromFactoryBean(FactoryBeanRegistrySupport.java:149)
at org.springframework.beans.factory.support.FactoryBeanRegistrySupport.getObjectFromFactoryBean(FactoryBeanRegistrySupport.java:102)
at org.springframework.beans.factory.support.AbstractBeanFactory.getObjectForBeanInstance(AbstractBeanFactory.java:1443)
at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:249)
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:194)
at org.springframework.context.support.AbstractApplicationContext.getBean(AbstractApplicationContext.java:1117)
at com.dhcc.advice.TestIntroduction.main(TestIntroduction.java:31)
Caused by: org.springframework.aop.framework.AopConfigException: Could not generate CGLIB subclass of class [class java.lang.String]:
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 java.lang.String
at org.springframework.aop.framework.CglibAopProxy.getProxy(CglibAopProxy.java:217)
at org.springframework.aop.framework.ProxyFactoryBean.getProxy(ProxyFactoryBean.java:362)
at org.springframework.aop.framework.ProxyFactoryBean.getSingletonInstance(ProxyFactoryBean.java:316)
at org.springframework.aop.framework.ProxyFactoryBean.getObject(ProxyFactoryBean.java:242)
at org.springframework.beans.factory.support.FactoryBeanRegistrySupport.doGetObjectFromFactoryBean(FactoryBeanRegistrySupport.java:142)
... 6 more
Caused by: java.lang.IllegalArgumentException: Cannot subclass final class class java.lang.String
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.create(Enhancer.java:285)
at org.springframework.aop.framework.CglibAopProxy.getProxy(CglibAopProxy.java:205)
... 10 more

这就是 sting   value="forumSrviceTarget"  报错，这里，不能用value要用ref

Could not generate CGLIB subclass of class [class java.lang.String]

<?xml version="1.0" encoding="UTF-8" ?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:p="http://www.springframework.org/schema/p"
xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.0.xsd"> 
<bean id="pmonitor" class="com.baobaotao.introduce.ControllablePerformaceMonitor" />
<bean id="forumServiceTarget" class="com.baobaotao.introduce.ForumService" />
<bean id="forumService" class="org.springframework.aop.framework.ProxyFactoryBean"
>

<property name="interfaces" value="com.baobaotao.introduce.Monitorable"></property>

<!-- 	<property name="target" value="forumServiceTarget"></property> -->
<!--    注意这里是ref而不是 value    -->

<property name="target" value="forumServiceTarget"></property>
<property name="interceptorNames" value="pmonitor"></property>
<property name="proxyTargetClass" value="true"></property>

</bean>
</beans>