>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>StandardWrapperValve--->Servlet>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

    请求转出，都由valve来调用servlet的service方法

    [1] 直接转出

    StandardWrapperValve

    void java.org.apache.catalina.core.StandardWrapperValve.invoke(Request request, Response response) throws IOException, ServletException

    --->filterChain.doFilter

    ------------>servlet.service(request, response);

    [2] 内部循环再转出

    -------->((AsyncContextImpl)request.getAsyncContext()).doInternalDispatch();

           ----> void java.org.apache.catalina.core.AsyncContextImpl.doInternalDispatch() throws ServletException, IOException

                ---->

                         Runnable runnable = dispatch;

                         dispatch = null;

                         runnable.run();

                         ------------->

                          void java.org.apache.catalina.core.AsyncContextImpl.dispatch(ServletContext context, String path)

                                 ---->applicationDispatcher.dispatch(servletRequest, servletResponse);

                                 AsyncDispatcher=applicationDispatcher

                                 final class ApplicationDispatcher implements AsyncDispatcher, RequestDispatcher

                                 ------>final class ApplicationDispatcher implements AsyncDispatcher, RequestDispatcher

                                         ---------> void java.org.apache.catalina.core.ApplicationDispatcher.doDispatch(ServletRequest request, ServletResponse response) throws ServletException, IOException

                                                    -------------> void java.org.apache.catalina.core.ApplicationDispatcher.doDispatch(ServletRequest request, ServletResponse response) throws ServletException, IOException

                                                                 //Servlet Service Method is called by the FilterChain

                                                                   ----------->void java.org.apache.catalina.core.ApplicationFilterChain.doFilter(ServletRequest request, ServletResponse response) throws IOException, ServletException

                                                                      --> void java.org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ServletRequest request, ServletResponse response) throws IOException, ServletException

                                                                             ------------>servlet.service(request, response);

     最终都是由servlet.service(request, response);

 >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>StandardWrapperValve--->Servlet>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>