Servlet 提供了四个封装类：
public class ServletRequestWrapper extends java.lang.Object implements ServletRequest // public class ServletResponseWrapper extends java.lang.Object implements ServletResponse // public class HttpServletRequestWrapper extends ServletRequestWrapper implements HttpServletRequest // public class HttpServletResponseWrapper extends ServletResponseWrapper implements HttpServletResponse //
直接扩展这些封装类就可以修饰相应的的 request 和 response 对象了。