Spring aop @target注解问题

Question

我用在spring aop拦截类上的注解的时候用了一个@target的限制匹配方法。但是在调试的时候提示如下错误：

org.springframework.context.ApplicationContextException: Unable to start embedded container; nested exception is org.springframework.boot.context.embedded.EmbeddedServletContainerException: Unable to start embedded Tomcat
    at org.springframework.boot.context.embedded.EmbeddedWebApplicationContext.onRefresh(EmbeddedWebApplicationContext.java:138)
    at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:536)
    at org.springframework.boot.context.embedded.EmbeddedWebApplicationContext.refresh(EmbeddedWebApplicationContext.java:123)
    at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:666)
    at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:353)
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:300)
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1082)
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1071)
    at com.example.springbootdemo.SpringbootdemoApplication.main(SpringbootdemoApplication.java:20)
Caused by: org.springframework.boot.context.embedded.EmbeddedServletContainerException: Unable to start embedded Tomcat
    at org.springframework.boot.context.embedded.tomcat.TomcatEmbeddedServletContainer.initialize(TomcatEmbeddedServletContainer.java:135)
    at org.springframework.boot.context.embedded.tomcat.TomcatEmbeddedServletContainer.<init>(TomcatEmbeddedServletContainer.java:87)
    at org.springframework.boot.context.embedded.tomcat.TomcatEmbeddedServletContainerFactory.getTomcatEmbeddedServletContainer(TomcatEmbeddedServletContainerFactory.java:535)
    at org.springframework.boot.context.embedded.tomcat.TomcatEmbeddedServletContainerFactory.getEmbeddedServletContainer(TomcatEmbeddedServletContainerFactory.java:177)
    at org.springframework.boot.context.embedded.tomcat.TomcatEmbeddedServletContainerFactory$$FastClassBySpringCGLIB$$bc74f446.invoke(<generated>)
    at org.springframework.cglib.proxy.MethodProxy.invoke(MethodProxy.java:204)
    at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.invokeJoinpoint(CglibAopProxy.java:736)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:157)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:173)
    at org.springframework.aop.interceptor.ExposeInvocationInterceptor.invoke(ExposeInvocationInterceptor.java:92)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
    at org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:671)
    at org.springframework.boot.context.embedded.tomcat.TomcatEmbeddedServletContainerFactory$$EnhancerBySpringCGLIB$$bda70dbb.getEmbeddedServletContainer(<generated>)
    at org.springframework.boot.context.embedded.EmbeddedWebApplicationContext.createEmbeddedServletContainer(EmbeddedWebApplicationContext.java:162)
    at org.springframework.boot.context.embedded.EmbeddedWebApplicationContext.onRefresh(EmbeddedWebApplicationContext.java:135)
    ... 8 common frames omitted
Caused by: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'metricsFilter' defined in class path resource [org/springframework/boot/actuate/autoconfigure/MetricFilterAutoConfiguration.class]: Initialization of bean failed; nested exception is org.springframework.aop.framework.AopConfigException: Could not generate CGLIB subclass of class org.springframework.boot.actuate.autoconfigure.MetricsFilter: 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 org.springframework.boot.actuate.autoconfigure.MetricsFilter
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:562)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:481)
    at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:312)
    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:230)
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:308)
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:202)
    at org.springframework.boot.web.servlet.ServletContextInitializerBeans.getOrderedBeansOfType(ServletContextInitializerBeans.java:212)
    at org.springframework.boot.web.servlet.ServletContextInitializerBeans.addAsRegistrationBean(ServletContextInitializerBeans.java:165)
    at org.springframework.boot.web.servlet.ServletContextInitializerBeans.addAsRegistrationBean(ServletContextInitializerBeans.java:160)
    at org.springframework.boot.web.servlet.ServletContextInitializerBeans.addAdaptableBeans(ServletContextInitializerBeans.java:145)
    at org.springframework.boot.web.servlet.ServletContextInitializerBeans.<init>(ServletContextInitializerBeans.java:78)
    at org.springframework.boot.context.embedded.EmbeddedWebApplicationContext.getServletContextInitializerBeans(EmbeddedWebApplicationContext.java:240)
    at org.springframework.boot.context.embedded.EmbeddedWebApplicationContext.selfInitialize(EmbeddedWebApplicationContext.java:214)
    at org.springframework.boot.context.embedded.EmbeddedWebApplicationContext.access$000(EmbeddedWebApplicationContext.java:91)
    at org.springframework.boot.context.embedded.EmbeddedWebApplicationContext$1.onStartup(EmbeddedWebApplicationContext.java:205)
    at org.springframework.boot.context.embedded.tomcat.TomcatStarter.onStartup(TomcatStarter.java:53)
    at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5154)
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
    at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1412)
    at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1402)
    at java.util.concurrent.FutureTask.run$$$capture(FutureTask.java:266)
    at java.util.concurrent.FutureTask.run(FutureTask.java)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
    at java.lang.Thread.run(Thread.java:748)
Caused by: org.springframework.aop.framework.AopConfigException: Could not generate CGLIB subclass of class org.springframework.boot.actuate.autoconfigure.MetricsFilter: 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 org.springframework.boot.actuate.autoconfigure.MetricsFilter
    at org.springframework.aop.framework.CglibAopProxy.getProxy(CglibAopProxy.java:209)
    at org.springframework.aop.framework.ProxyFactory.getProxy(ProxyFactory.java:109)
    at org.springframework.aop.framework.autoproxy.AbstractAutoProxyCreator.createProxy(AbstractAutoProxyCreator.java:463)
    at org.springframework.aop.framework.autoproxy.AbstractAutoProxyCreator.wrapIfNecessary(AbstractAutoProxyCreator.java:346)
    at org.springframework.aop.framework.autoproxy.AbstractAutoProxyCreator.postProcessAfterInitialization(AbstractAutoProxyCreator.java:295)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.applyBeanPostProcessorsAfterInitialization(AbstractAutowireCapableBeanFactory.java:421)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1634)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:553)
    ... 24 common frames omitted
Caused by: java.lang.IllegalArgumentException: Cannot subclass final class org.springframework.boot.actuate.autoconfigure.MetricsFilter
    at org.springframework.cglib.proxy.Enhancer.generateClass(Enhancer.java:565)
    at org.springframework.cglib.transform.TransformingClassGenerator.generateClass(TransformingClassGenerator.java:33)
    at org.springframework.cglib.core.DefaultGeneratorStrategy.generate(DefaultGeneratorStrategy.java:25)
    at org.springframework.aop.framework.CglibAopProxy$ClassLoaderAwareUndeclaredThrowableStrategy.generate(CglibAopProxy.java:1001)
    at org.springframework.cglib.core.AbstractClassGenerator.generate(AbstractClassGenerator.java:329)
    at org.springframework.cglib.proxy.Enhancer.generate(Enhancer.java:492)
    at org.springframework.cglib.core.AbstractClassGenerator$ClassLoaderData$3.apply(AbstractClassGenerator.java:93)
    at org.springframework.cglib.core.AbstractClassGenerator$ClassLoaderData$3.apply(AbstractClassGenerator.java:91)
    at org.springframework.cglib.core.internal.LoadingCache$2.call(LoadingCache.java:54)
    at java.util.concurrent.FutureTask.run$$$capture(FutureTask.java:266)
    at java.util.concurrent.FutureTask.run(FutureTask.java)
    at org.springframework.cglib.core.internal.LoadingCache.createEntry(LoadingCache.java:61)
    at org.springframework.cglib.core.internal.LoadingCache.get(LoadingCache.java:34)
    at org.springframework.cglib.core.AbstractClassGenerator$ClassLoaderData.get(AbstractClassGenerator.java:116)
    at org.springframework.cglib.core.AbstractClassGenerator.create(AbstractClassGenerator.java:291)
    at org.springframework.cglib.proxy.Enhancer.createHelper(Enhancer.java:480)
    at org.springframework.cglib.proxy.Enhancer.createClass(Enhancer.java:337)
    at org.springframework.aop.framework.ObjenesisCglibAopProxy.createProxyClassAndInstance(ObjenesisCglibAopProxy.java:54)
    at org.springframework.aop.framework.CglibAopProxy.getProxy(CglibAopProxy.java:201)
    ... 31 common frames omitted

主要是这个错误，就是无法用cglib代理一个final的类

Cannot subclass final class org.springframework.boot.actuate.autoconfigure.MetricsFilter

我的切点是这样的

    @Pointcut("@target(com.example.springbootdemo.aspect.TimeIt)")
    public void calcTime() {}

其中TimeIt是一个注解

@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.TYPE,ElementType.METHOD})
public @interface TimeIt {
    boolean enabled() default true;
}

我把切点改成这样就可以运行了

    @Pointcut("@within(com.example.springbootdemo.aspect.TimeIt)")
    public void calcTime() {}

我不太理解的是MetricsFilter这个类上并没有这个注解，为什么会去生成代理呢？
有没有大神懂的，麻烦指点一下，多谢