我有下一个问题......当我提交表单并且我的 Post 方法结束时。表单(或不)抛出空警报窗口。我怎样才能删除这个投掷窗口?
客户端
 ....            
        final FormPanel form = new FormPanel();
        form.setAction(GWT.getModuleBaseURL()+"upload");
        form.setEncoding(FormPanel.ENCODING_MULTIPART);
        form.setMethod(FormPanel.METHOD_POST);
        VerticalPanel panel = new VerticalPanel();
        form.setWidget(panel);
        FileUpload upload = new FileUpload();
        upload.setName("uploadFormElement");
        panel.add(upload);
        fileButton.addClickHandler(new ClickHandler() {
            public void onClick(ClickEvent event) {
                form.submit();
            }
        });
FileUploadServlet
public class FileUploadServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException {
        super.doGet(req, resp);
    }
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException {
        if (ServletFileUpload.isMultipartContent(req)) {   
            FileItemFactory factory = new DiskFileItemFactory();
            ServletFileUpload upload = new ServletFileUpload(factory);
            try {
                List<FileItem> items = upload.parseRequest(req);
                for (FileItem fileItem : items) {
                    if (fileItem.isFormField()) continue;
                    String fileName = fileItem.getName();
                    if (fileName != null) {
                        fileName = FilenameUtils.getName(fileName);
                    }
                    File uploadedFile = new File("test.txt");
                    if (uploadedFile.createNewFile()) {
                        fileItem.write(uploadedFile);
                    }
                }
            } catch (FileUploadException e) {
                e.printStackTrace();
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }
也许有人知道这个警报的原因?