GWT getResults () SubmitCompleteEvent returns null after submitting form with FileUpload

After successfully implementing file upload using GWT

in one application, I tried to port this to another application, but the string returned from the boot servlet cannot be restored in the provided one SubmitCompleteHandler

. SubmitCompleteEvent.getResults()

just returns null.

The typical reason for returning null seems to be because the upload servlet is on a different domain. But since GWT and the loading servlet run in the same context, this shouldn't be a cross-domain access issue.

The widget is FileUpload

contained in FormPanel

. When the button is clicked, the form is submitted. This calls the servlet (indeed, a breakpoint is hit during debugging). In the real world it will save the file on the server side and return the filename. In this given example, it just writes a String to the Writer response.

FormPanel

with a FileUpload

snippet:

final FormPanel form = new FormPanel();
form.setAction("upload"); // results "upload" directly below context
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);

panel.add(new Button("Submit", new ClickHandler() {
    public void onClick(ClickEvent event) {
        form.submit();
    }
}));
form.addSubmitCompleteHandler(new FormPanel.SubmitCompleteHandler() {
    public void onSubmitComplete(SubmitCompleteEvent event) {
        Window.alert("===> " + event.getResults() + " <==="); // shows "===> null <==="
    }
});

      

        
        
        
      

    

web.xml

fragment:

<servlet> 
    <servlet-name>FileUploadServlet</servlet-name>
    <servlet-class>mypackage.FileUploadServlet</servlet-class> 
</servlet> 
<servlet-mapping>
    <servlet-name>FileUploadServlet</servlet-name>
    <url-pattern>/upload</url-pattern> 
</servlet-mapping>

      

        
        
        
      

    

FileUploadServlet

fragment:

public class FileUploadServlet extends HttpServlet {

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse response)
            throws ServletException, IOException {

        response.setContentType("text/html");
        response.getWriter().write("OK");
        response.getWriter().flush();
    }

}

      

        
        
        
      

    

Are there libraries or libraries known to conflict with the GWT SubmitCompleteHandler?

Any ideas are appreciated ...

UPDATE : After downgrading all artifacts belonging to spring-security from 4.0.4.RELEASE to 3.2.4.RELEASE, it works. With updating them to 4.1.2.RELEASE it doesn't work either.