Get file in a gwt

Hi all! Sorry but I have some dudes.

I want fill a ListBox (gwt) with a file txt. But some issues happen. I am doing a RequestBuilder in the widget

            Request request = builder.sendRequest(null, new RequestCallback() {
                public void onError(Request request, Throwable exception) {
                    displayError("Couldn't retrieve txt");
                }

                public void onResponseReceived(Request request,
                        Response response) {
                    if (200 == response.getStatusCode()) {
                        getFile(response.getText());
                    } else {
                        LOGGER.info("404!!!");    }
                }
            });
        } catch (RequestException e) {
            displayError("Couldn't retrieve txt");
        }

and in a servlet the next:

@Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException {
        String rootPath = "";
            rootPath = System.getProperty("catalina.home");
        File file = new File(rootPath+ File.separator +"file.txt");
        if (!file.exists()) {
            throw new ServletException("File doesn't exists on server: " + context);
        }
        InputStream fis = new FileInputStream(file);
        String mimeType = ctx.getMimeType(file.getAbsolutePath());
        resp.setContentType(mimeType != null ? mimeType
                : "application/octet-stream");
        resp.setContentLength((int) file.length());
        resp.setHeader("Content-Disposition", "attachment; filename=\""
                + "one.txt" + "\"");
        ServletOutputStream os = resp.getOutputStream();
        byte[] bufferData = new byte[1024];
        int read = 0;
        while ((read = fis.read(bufferData)) != -1) {
            os.write(bufferData, 0, read);
        }
        os.flush();
        os.close();
        fis.close();
        System.out.println("File downloaded at client successfully");
    }

But doesn't works. Never enters in the doGet. And I test the widget (without vaadin implementations, only with the google toolkit) and works. I don't know if I have to send a Vaddin Request in the doGet or something like that.

Thank you so much!