Handle attachment in response with RequestBuilder in GWT

I am making a HTTP POST request from GWT Client to a HTTPServlet. This Servlet is creating a PDF file from request content and writing it to response stream.

Headers of the response stream are:

Content-Disposition: attachment; filename=report.pdf

I want to open this PDF in new window of the user's browser or prompt him to download it.

import com.google.gwt.http.client.*;
...

String url = "http://www.myserver.com/getData?type=3";
RequestBuilder builder = new RequestBuilder(RequestBuilder.POST, URL.encode(url));

try {
  Request request = builder.sendRequest(data, new RequestCallback() {
    public void onError(Request request, Throwable exception) {
       // Couldn't connect to server (could be timeout, SOP violation, etc.)     
    }

    public void onResponseReceived(Request request, Response response) {
      if (200 == response.getStatusCode()) {
          // Process the response in response.getText()
          // Window.open(url, "_blank", "");
      } else {
        // Handle the error.  Can get the status text from response.getStatusText()
      }
    }       
  });
} catch (RequestException e) {
  // Couldn't connect to server        
}

How should I handle response in onResponseRecieved?