如何使用iText旋转PDF中的水印(文本)?

我使用iText在PDF文件上打上水印(文本:“SuperEasy You Done”),如中所述 How to watermark PDFs using text or images? ( TransparentWatermark2.java See project source code on GitHub

现在我得到的PDF的一个例子是 this one (本文件其余部分略去):

如您所见,水印居中且水平。

我想去 在页面中间,但是 旋转45度 ,所以它逆时针旋转。像这样:

This is the code 用于在给定字节数组上加盖水印(pdf文档目前仅适用于我)

/**
 * Returns the same document with the watermark stamped on it.
 * @param documentBytes Byte array of the pdf which is going to be returned with the watermark
 * @return byte[] with the same byte array provided but now with the watermark stamped on it.
 * @throws IOException If any IO exception occurs while adding the watermark
 * @throws DocumentException If any DocumentException exception occurs while adding the watermark
 */
private byte[] getDocumentWithWaterMark(byte[] documentBytes) throws IOException, DocumentException {
    ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
    // pdf
    PdfReader reader = new PdfReader(documentBytes);
    int n = reader.getNumberOfPages();
    PdfStamper stamper = new PdfStamper(reader, outputStream);
    // text watermark
    Font font = new Font(Font.HELVETICA, 60);
    Phrase phrase = new Phrase("SuperEasy You Done", font);
    // transparency
    PdfGState gs1 = new PdfGState();
    gs1.setFillOpacity(0.06f);
    // properties
    PdfContentByte over;
    Rectangle pagesize;
    float x, y;
    // loop over every page (in case more than one page)
    for (int i = 1; i <= n; i++) {
        pagesize = reader.getPageSizeWithRotation(i);
        x = (pagesize.getLeft() + pagesize.getRight()) / 2;
        y = (pagesize.getTop() + pagesize.getBottom()) / 2;
        over = stamper.getOverContent(i);
        over.saveState();
        over.setGState(gs1);
        // add text
        ColumnText.showTextAligned(over, Element.ALIGN_CENTER, phrase, x, y, 0);
        over.restoreState();
    }
    stamper.close();
    reader.close();
    return outputStream.toByteArray();
}

附言:我读了这篇文章,但没用:

• http://itext.2136553.n4.nabble.com/rotate-a-watermark-td2155042.html