GWT File Upload form submit POST request not able to read file

Question

I have tried FileUpload referring GWT source doc. Since I wanted to add it on different tab I have created GWT page for that and added FileUpload over there. Not implmented entryPoint since its been implemented in their root page. I am not using onModuleLoad method I am just creating method to display element and adding it to FormPanel.

I am able to submit POST request but not able to capture File on servlet. Am I doing something wrong at GWT side or servlet Side.

I have used similar kind of code at GWT side

public class FormPanelExample implements Composite {

  public void FormPanelExample() {
    // Create a FormPanel and point it at a service.
    final FormPanel form = new FormPanel();
    form.setAction("/myFormHandler");

    // Because we're going to add a FileUpload widget, we'll need to set the
    // form to use the POST method, and multipart MIME encoding.
    form.setEncoding(FormPanel.ENCODING_MULTIPART);
    form.setMethod(FormPanel.METHOD_POST);

    // Create a panel to hold all of the form widgets.
    VerticalPanel panel = new VerticalPanel();
    form.setWidget(panel);

    // Create a TextBox, giving it a name so that it will be submitted.
    final TextBox tb = new TextBox();
    tb.setName("textBoxFormElement");
    panel.add(tb);

    // Create a ListBox, giving it a name and some values to be associated with
    // its options.
    ListBox lb = new ListBox();
    lb.setName("listBoxFormElement");
    lb.addItem("foo", "fooValue");
    lb.addItem("bar", "barValue");
    lb.addItem("baz", "bazValue");
    panel.add(lb);

    // Create a FileUpload widget.
    FileUpload upload = new FileUpload();
    upload.setName("uploadFormElement");
    panel.add(upload);

    // Add a 'submit' button.
    panel.add(new Button("Submit", new ClickHandler() {
      public void onClick(ClickEvent event) {
        form.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 (tb.getText().length() == 0) {
          Window.alert("The text box must not be empty");
          event.cancel();
        }
      }
    });
    form.addSubmitCompleteHandler(new FormPanel.SubmitCompleteHandler() {
      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());
      }
    });

    RootPanel.get().add(form);
  }
}

At Servlet side

if (!ServletFileUpload.isMultipartContent(request)) {                                 
            throw new FileUploadException("error multipart request not found");              
        }       

        DiskFileItemFactory factory = new DiskFileItemFactory();            

        ServletFileUpload upload = new ServletFileUpload(factory);

        List<FileItem> items = upload.parseRequest(request);

        if (items == null) {            
            response.getWriter().write("File not correctly uploaded");
            return;
        }

        Iterator<FileItem> iter = items.iterator();

When I am calling iter.next(), it gives error no such elementFound Exception By exception it looks to be on submit file is not submitting to servlet request.

Answer 1

Try using postman to call the endpoint and upload a file directly to your running Servlet to ensure that is working correctly.

I checked my own implementation of this code and it almost matches yours exactly, except I'm not using anything but the FileUpload on the panel. Remove the TextBox and ListBox so we can check that just the file part is working on its own, then introduce each item and test it separately.

I found this to be more reliable on the server side

FileItemFactory factory = new DiskFileItemFactory();
ServletFileUpload servletFileUpload = new ServletFileUpload(factory);
FileItemIterator iter = servletFileUpload.getItemIterator(request);