Servlet生命周期中的service方法分析

问题
ServletLifeCycle中的service方法内,有super.service(request, response); 会执行this.doGet(HttpServletRequest request, HttpServletResponse response);
没有super.service(request, response);,则不执行this.doGet(...). 是怎么实现的?

举一反三:
一个子类,覆写的方法内,如果调用了父类的该方法,会执行子类内的另一个方法;
覆写的方法内,如果没有调用父类的该方法,就不会执行子类内的另一个方法;

分析 ----->符号是关键注释

 public class ServletLifeCycle extends HttpServlet {
     private static final long serialVersionUID = 1L;

     @Override
     public void service(ServletRequest request, ServletResponse response) throws ServletException, IOException {
         // TODO Auto-generated method stub
         //this.doGet((HttpServletRequest)request, (HttpServletResponse)response);
         super.service(request, response);//------------------->执行父类的service(ServletRequest request, ServletResponse response)方法

         System.out.println("处理客户端请求");
     }

     protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
         // TODO Auto-generated method stub
         System.out.println("处理过程");
         response.getWriter().append("Served at: ").append(request.getContextPath());
     }

 }

 public abstract class HttpServlet extends GenericServlet {
 public void service(ServletRequest req, ServletResponse res)
     throws ServletException, IOException {

     HttpServletRequest  request;
     HttpServletResponse response;

     try {
         request = (HttpServletRequest) req;
         response = (HttpServletResponse) res;
     } catch (ClassCastException e) {
         throw new ServletException("non-HTTP request or response");
     }
     service(request, response);//------------------->父类的方法的重载执行父类的service(HttpServletRequest request, HttpServletResponse response)方法
     //------------------->我的理解是,如果没有重载,会出现死循环.   走到此处又执行子类ServletLifeCycle的service方法,子类又调用父类service方法,循环嵌套.
 }

 protected void service(HttpServletRequest req, HttpServletResponse resp)
         throws ServletException, IOException {

         String method = req.getMethod();

         if (method.equals(METHOD_GET)) {
             long lastModified = getLastModified(req);
             if (lastModified == -1) {
                 // servlet doesn't support if-modified-since, no reason
                 // to go through further expensive logic
                 doGet(req, resp);//------------------->调用子类ServletLifeCycle的doGet方法
             } else {
                 long ifModifiedSince;
                 try {
                     ifModifiedSince = req.getDateHeader(HEADER_IFMODSINCE);
                 } catch (IllegalArgumentException iae) {
                     // Invalid date header - proceed as if none was set
                     ifModifiedSince = -1;
                 }
                 if (ifModifiedSince < (lastModified / 1000 * 1000)) {
                     // If the servlet mod time is later, call doGet()
                     // Round down to the nearest second for a proper compare
                     // A ifModifiedSince of -1 will always be less
                     maybeSetLastModified(resp, lastModified);
                     doGet(req, resp);
                 } else {
                     resp.setStatus(HttpServletResponse.SC_NOT_MODIFIED);
                 }
             }

         } else if (method.equals(METHOD_HEAD)) {
             long lastModified = getLastModified(req);
             maybeSetLastModified(resp, lastModified);
             doHead(req, resp);

         } else if (method.equals(METHOD_POST)) {
             doPost(req, resp);

         } else if (method.equals(METHOD_PUT)) {
             doPut(req, resp);

         } else if (method.equals(METHOD_DELETE)) {
             doDelete(req, resp);

         } else if (method.equals(METHOD_OPTIONS)) {
             doOptions(req,resp);

         } else if (method.equals(METHOD_TRACE)) {
             doTrace(req,resp);

         } else {
             //
             // Note that this means NO servlet supports whatever
             // method was requested, anywhere on this server.
             //

             String errMsg = lStrings.getString("http.method_not_implemented");
             Object[] errArgs = new Object[1];
             errArgs[0] = method;
             errMsg = MessageFormat.format(errMsg, errArgs);

             resp.sendError(HttpServletResponse.SC_NOT_IMPLEMENTED, errMsg);
         }
     }

 protected void doGet(HttpServletRequest req, HttpServletResponse resp)
     throws ServletException, IOException
 {
     String protocol = req.getProtocol();
     String msg = lStrings.getString("http.method_get_not_supported");
     if (protocol.endsWith("1.1")) {
         resp.sendError(HttpServletResponse.SC_METHOD_NOT_ALLOWED, msg);
     } else {
         resp.sendError(HttpServletResponse.SC_BAD_REQUEST, msg);
     }
 }
 }