WebApplicationException thrown when trying to stream download file

[Pauline McCall]

I am accessing a URL that downloads an xls file. I had code that saved it first, then streamed it to the user via Desktop.getDesktop().open(file);

However, I now would prefer to do it in the one step, access the file and stream it straight to the user. I have updated my code but everytime it downloads the file, I get this output:
WARN o.a.c.j.i.WebApplicationExceptionMapper - WebApplicationException has been caught : no cause is available

This is my code:

 url = "xxx";
  HttpClient client = new HttpClient();
        KerberizedNetegrityClient auth;       
        try {
            auth = new KerberizedNetegrityClient();
            cookie = auth.getCookieToken();
        } catch (NetegrityClientException e) {...}

 GetMethod method = new GetMethod(url);
        
        method.getParams().setParameter(HttpMethodParams.RETRY_HANDLER, new DefaultHttpMethodRetryHandler(3, false));
        method.setRequestHeader("Cookie", cookie);

 if(contentType.equals("application/octet-stream")){                 
                file = new File("xxxx");

                InputStream is = method.getResponseBodyAsStream();
                FileOutputStream fos = new FileOutputStream(file);
                byte kb[] = new byte[1024];
                int i=-1;
                while((i=is.read(kb))>-1) fos.write(i);
                fos.flush();
                fos.close();