用CGLib对Tomcat的RequestFacade类构造动态代理类时发生的类型转换异常

Question

我想在过滤器里返回代理后的servletrequest,发现其底层是tomcat的catlina包下的RequestFacade类,所以准备对它用cglib进行代理,增强其方法,此时发现对servletrequest强类转为RequestFacade时,报异常:
org.apache.catalina.connector.RequestFacade cannot cast to org.apache.catalina.connector.RequestFacade
RequestFacade这个类的包我是在lib中放入了tomcat/lib下的catlina.jar后才有的,这个包应该就是tomcat使用的包,请问问题出在哪里呢?~~

    public void doFilter(ServletRequest servletrequest,
            ServletResponse servletresponse, FilterChain filterchain)
            throws IOException, ServletException {
        //此处发生类型转换异常
        RequestFacade request = (RequestFacade)servletrequest;
        HttpServletResponse response = (HttpServletResponse)servletresponse;
        HttpServletRequest newrequest=new CGLibProxy(request).createProxy();
        String testString = newrequest.getRequestURL().toString();
        System.out.println(testString);
        filterchain.doFilter(newrequest, response);
    }

Answer 1

传进来的requestfecade应该是由加载tomcat lib的类加载器加载的，而前面的requestfacade和当前filter类是同一个类加载器，而后面的类加载器
是filter类的父类加载器，所以无法从父类加载器转向子类，也有可能二者没有继承关系，没有试验，但是应该是这个原因导致的