GWT Progress Bar while buffering PDF content before displaying on browser - gwt

Question

In my GWT app I have written a servlet to download/stream a PDF file.
Following is the code.
protected void updateResponse(HttpServletResponse response, InputStream dataStream, long contentLength, KnownContentTypes contentType, String filename, int cacheSeconds) {
response.setHeader("Content-Type", contentType.getTypeString());
response.setHeader("Content-Length", String.valueOf(contentLength));
response.setHeader("Content-disposition", "inline;filename=" + filename);
response.setHeader("Cache-Control", "max-age=" + cacheSeconds);
byte[] buffer = new byte[BUFFER_SIZE];
try {
ServletOutputStream out = response.getOutputStream();
while ((dataStream.read(buffer)) != -1) {
out.write(buffer);
}
} catch (IOException e) {
sendError(response);
}
}
The pdf is successfully rendered on the browser.
The problem is some pdf's are really large in size and since this is called on window.open all I see is a blank browser.
I want to display a dynamic message like '1MB of 5MB downloaded' and display/render the entire PDF file once all bytes are streamed.
Please let me know how to do this.
I am new to GWT and any help will be appreciated.
Thanks.

Answer 1

This can not be done with synch request which we usually make by calling servlet with Window.open You have to make ajax request to calculate progress and display the response.
Take a look to this library: http://code.google.com/p/gwtupload/. It is really easy to to use and works fine in most of the browsers. It uses ajax requests to calculate progress.