Iframe: blank page invoking a servlet which produces a pdf outputstream (using Mozilla Firefox)

<window title="---" width="90%" height="90%" mode="modal" border="normal" closable="true">

	<zscript>
		labelsPDFDocuments = ...   // servlet to invoke plus parameters
	</zscript>
	<iframe id="iframe" src="${labelsPDFDocuments}" width="100%" height="100%"/>
	
	<attribute name="onCreate">
		self.setParent(parentWin);
	</attribute>
	<attribute name="onClose">
		FileUtil.deleteLabelFiles(labelsPDFDocuments.substring(labelsPDFDocuments.indexOf("=") + 1), "|");
	</attribute>
</window>

public class LabelViewerServlet extends HttpServlet {

	private static final long serialVersionUID = -7306259114973684722L;

	private static final String K_PARM_LABELS = "labels";

	private static final String K_HTML_MIME_TYPE = "text/html";
	private static final String K_PDF_MIME_TYPE = "application/pdf";

	protected void doGet(HttpServletRequest request,
			HttpServletResponse response) throws ServletException, IOException {
		try {
			process(request, response);
		} catch (Exception e) {
			response.setContentType(K_HTML_MIME_TYPE);
			response.getOutputStream().println(e.toString());
		}
	}

	private void process(HttpServletRequest a_request,
			HttpServletResponse a_response) throws Exception {

		// gets the list of pdf files to concatenate (they are specified as labels=filename1.pdf|filename2.pdf|filename3.pdf
		String ls_labelsPDF = a_request.getParameter(K_PARM_LABELS);
		if (StringUtil.isEmpty(ls_labelsPDF))
			throw new Exception("Error...");

		StringTokenizer l_lpst = new StringTokenizer(ls_labelsPDF, "|");

		ArrayList<InputStream> l_labelsPDF = new ArrayList<InputStream>(5);
		while (l_lpst.hasMoreTokens()) {
			String ls_labelPDF = l_lpst.nextToken();
			l_labelsPDF.add(new FileInputStream(this.getServletContext().getRealPath("/labels") + "\\" + ls_labelPDF));
		}

		a_response.setContentType(K_PDF_MIME_TYPE);

		OutputStream l_os = a_response.getOutputStream();

		// merging...
		PdfUtil.mergePdf(l_labelsPDF, l_os);

		l_os.flush();
		l_os.close();

	}
}