Cannot draw elements on already flushed pages

问题:

I wanted to generate the pdf with page numbers and also having table of content which has page numbers in it. I am up to generating PDF but cannot add page numbers to it.

ol.anchorLink a::after {  
    content: leader('.') target-counter(attr(href), page);
}
@page {
    @bottom-right { 
        padding-right:20px; 
        content: "Page " counter(page); 
    } 
}

this piece of cs is not woking in the dependency i am using which is itextpdf. so I have made changes in the java file

 @Override
public DataHandler getPDFVersion(StringBuffer htmlSrc, String documentTitle) throws Exception {
    DataHandler dataHandler = null;
    String outputFile = "test.pdf";

    try (InputStream inputStream = new ByteArrayInputStream(htmlSrc.toString().getBytes());
            OutputStream os = new FileOutputStream(new File(outputFile));) {
        ConverterProperties converterProperties = new ConverterProperties();
        PdfWriter writer = new PdfWriter(os, new WriterProperties().setFullCompressionMode(true));
        PdfDocument pdfDoc = new PdfDocument(writer);
        List<IElement> elements = HtmlConverter.convertToElements(inputStream, converterProperties);
        Document document = new Document(pdfDoc);
        document.setProperty(Property.SPLIT_CHARACTERS, new DefaultSplitCharacters() {
            @Override
            public boolean isSplitCharacter(GlyphLine text, int glyphPos) {
                return true;
            }
        });


            for (IElement element : elements) {
            if (element instanceof AreaBreak) {
                document.add((AreaBreak) element);
            } else {
                document.add((IBlockElement) element);
            }
        }

            int n = pdfDoc.getNumberOfPages();
            for(int i=1; i<=n; i++)
            {
                document.showTextAligned(new Paragraph(String.format("page %s of %s", i, n)),
                        559, 806, i, TextAlignment.RIGHT, VerticalAlignment.TOP, 0);
            }
        int g= pdfDoc.getNumberOfPages();
        document.close();
        dataHandler = new DataHandler(new FileDataSource(outputFile));
        } catch (Exception e) {
        //do not throw error
        log.error("Error @ getPDFVersion() :" + e);
    }
    return dataHandler;
}

and When the run the PDF I am getting exception saying com.itextpdf.kernel.PdfException: Cannot draw elements on already flushed pages. so I have moved code before IELEMENT there I am able to print the page numbers of pdf but If I hard code the value. page number is 0 I think may be PDF is not generated by then how to solve this issue?