检查窗口是否已经关闭的问题

Question

try
        {
            String s4 = "/work/UploadRzDataFile.jsp";
            RequestDispatcher requestdispatcher = getServletContext().getRequestDispatcher(s4);
            if(requestdispatcher != null)
                requestdispatcher.forward(httpservletrequest, httpservletresponse);
            else
                System.out.println("gotoPage failed: RequestDispatcher is null.");
        }
        catch(Exception exception)
        {
            System.out.println("gotoPage error: " + exception.getMessage());
            exception.printStackTrace();
            httpservletrequest.setAttribute("_error", "gotoPage failed: " + exception.toString());
         
        }