SpringBoot - Generate pdf using flying-saucer-pdf result into empty file

Question

I'am tying to export a pdf file from html using fly-saucer, but the file is always empty and therefore can not be opened. Can anyone tell me what i am doing wrong.

Here is my current code:

        String templateName = "test-pdf";
        Context ctx = new Context();
        String processedHtml = templateEngine.process(templateName, ctx);

        ITextRenderer renderer = new ITextRenderer();
        renderer.setDocumentFromString(processedHtml);
        renderer.layout();

        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        renderer.createPDF(baos, false);

        // setting some response headers
        response.setHeader("Expires", "0");
        response.setHeader("Cache-Control",
                "must-revalidate, post-check=0, pre-check=0");
        response.setHeader("Pragma", "public");
        // setting the content type
        response.setContentType("application/pdf");
        // the contentLength
        response.setContentLength(baos.size());

        OutputStream os = response.getOutputStream();
        baos.writeTo(os);
        os.flush();
        os.close();

        System.out.println("PDF created successfully");