Java servlet 未触发 onSubmitComplete（Google 应用引擎）答案

【问题标题】：Java servlet not firing onSubmitComplete (Google app engine)Java servlet 未触发 onSubmitComplete（Google 应用引擎）
【发布时间】：2014-03-11 08:54:15
【问题描述】：

GWT 2.5.1/ App Engine SDK 1.8.9

我正在尝试将 .CVS 文件上传到要使用 FormPanel 解析的 servlet，但是我没有收到 servlet 的响应。

客户端代码

// Create a FormPanel and point it at a service
    final FormPanel form = new FormPanel();
    form.setAction(GWT.getModuleBaseURL() + "uploadServlet");
    System.out.println(GWT.getModuleBaseURL() + "uploadServlet");
            //gives me http:// . .  . /healthybc/uploadServlet

    // set form to use the POST method, and multipart MIME encoding
    form.setEncoding(FormPanel.ENCODING_MULTIPART);
    form.setMethod(FormPanel.METHOD_POST);
    form.setWidget(buttonPanel);


    final FileUpload fileUpload = new FileUpload();
    fileUpload.setName("Browse");
    buttonPanel.add(fileUpload);

    // Add a 'submit' button.
    Button submit = new Button("Submit");
    submit.addClickHandler(new ClickHandler() {
        @Override
        public void onClick(ClickEvent event) {
            form.submit();                              
        }
    });

    buttonPanel.add(submit);

    // Add an event handler to the form.
    form.addSubmitHandler(new FormPanel.SubmitHandler() {
        public void onSubmit(SubmitEvent event) {
            // This event is fired just before the form is submitted. We can take
            // this opportunity to perform validation.

            if (fileUpload.getFilename().length() == 0) {
                Window.alert("The text box must not be empty");
                event.cancel();
            }
            else if (!fileUpload.getFilename().endsWith(".csv")){
                Window.alert("Can only upload .csv files");
                event.cancel();
            }

        }
    });

    form.addSubmitCompleteHandler(new FormPanel.SubmitCompleteHandler() {
        @Override
        public void onSubmitComplete(SubmitCompleteEvent event) {
          // When the form submission is successfully completed, this event is
          // fired. Assuming the service returned a response of type text/html,
          // we can get the result text here (see the FormPanel documentation for
          // further explanation).

          Window.alert(event.getResults());
        }
      });

我从 onSubmit() 得到窗口，但从 onSubmitComplete 没有响应。

web.xml

服务器代码

public class UploadedCSVParser extends HttpServlet{   
@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException 
{
    doPost(request, response);
}

@Override
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException 
{
    response.setContentType("text/html");
    PrintWriter out = response.getWriter();


    out.println("<html>");
             out.println("<head>");
             out.println("<title> servlet title</title>");
             out.println("</head>");
              out.println("<body>");
              out.println("</body>");

         out.println("TEXT GOES HERE");

                out.println("</html>");
                out.close();


}

现在服务器代码就在那里，看看我是否真的得到了响应。在我的浏览器（我使用的是 firefox）中直接输入 URL ...“/healthybc/uploadServlet”会给我预期的“TEXT GOES HERE”输出，但我没有收到任何迹象表明提交表单时 onSubmitComplete 曾经运行过。我开始认为信息永远不会到达 servlet。

我做错了吗？有什么简单的方法可以检查 servlet 是否真的被调用了？

【问题讨论】：

标签： java google-app-engine servlets gwt

【解决方案1】：

我以某种方式修复了它。我从一个已知的工作模板重做了客户端，我认为它的顺序可能与我最初的顺序略有不同。

    final FormPanel form = new FormPanel();
    form.setMethod(FormPanel.METHOD_POST);
    form.setEncoding(FormPanel.ENCODING_MULTIPART);
    form.setAction("/healthybc/uploadServlet");

        // then there's a button they can click which calls form.submit();
    form.setWidget(new Button("Submit", (new ClickHandler() {
      @Override
      public void onClick(ClickEvent event) {
        form.submit();
      }
    })));

    buttonPanel.add(form);

    final FileUpload fileUpload = new FileUpload();
    fileUpload.setName("Browse");
    buttonPanel.add(clinicFileUpload);

    // Add an event handler to the form.
    form.addSubmitHandler(new FormPanel.SubmitHandler() {
        public void onSubmit(SubmitEvent event) {
            // This event is fired just before the form is submitted. We can take
            // this opportunity to perform validation.

            if (fileUpload.getFilename().length() == 0) {
                Window.alert("The text box must not be empty");
                event.cancel();
            }
            else if (!fileUpload.getFilename().endsWith(".csv")){
                Window.alert("Can only upload .csv files");
                event.cancel();
            }

        }
    });

    form.addSubmitCompleteHandler(new FormPanel.SubmitCompleteHandler() {
        @Override
        public void onSubmitComplete(SubmitCompleteEvent event) {
          // When the form submission is successfully completed, this event is
          // fired. Assuming the service returned a response of type text/html,
          // we can get the result text here (see the FormPanel documentation for
          // further explanation).
          Window.alert(event.getResults());
        }
      });

【讨论】：