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);
    }
}
}