java - 使用 iText 旋转 PdfSignatureAppearance

Question

我在尝试在 iText 中旋转 PdfSignatureAppearance(例如 90 度)时遇到了一个大问题。我正在使用 MakeSignature.signDetached 方法签署 PDF，并为外观设置我自己的文本和图像。

这是一些代码:

PdfReader reader = new PdfReader("my input file");
FileOutputStream fout = new FileOutputStream("my output file");

PdfStamper stamper = PdfStamper.createSignature(reader, fout, '\0');
PdfSignatureAppearance sap = stamper.getSignatureAppearance();

sap.setLayer2Text("Signed by someone");
sap.setAcro6Layers(true);
sap.setSignatureGraphic("my signature image", null));
sap.setRenderingMode(PdfSignatureAppearance.RenderingMode.GRAPHIC_AND_DESCRIPTION);

Rectangle pageSize = reader.getPageSize(1); //the page to sign: 1 is the 1st one

Rectangle rect = new Rectangle(llx, lly, urx, ury, rotation);
//llx, lly ... come from a GUI. They are working fine, but the rotation is not considered

sap.setVisibleSignature(rect, 1, null); //1 is the page to sign

MakeSignature.signDetached(sap, ...); //sign the document

我的问题是“旋转”参数。无论我设置什么，文本和图像都不会旋转。查看 iText 代码(我使用的是 iText 5.3.2)，签名层边界框的旋转参数被丢弃，所以，以这种方式设置旋转根本没有效果。

现在的问题是:有没有一种方法可以在不重写整个 PdfSignatureAppearance 和 MakeSignature 类的情况下旋转我的签名层？

澄清一下:对文档进行数字签名的代码工作正常。我唯一的问题是签名的可视层:我无法旋转它。

谢谢。

Answer 1

允许重用 com.itextpdf.text.pdf.PdfSignatureAppearance 中代码的工作示例(例如自动计算字体大小):

public class RotateVisualSignature {
    public static void main(String[] args) throws IOException, DocumentException, GeneralSecurityException {
        // Loading private key and certificates.
        KeyStore keyStore = KeyStore.getInstance("PKCS12");
        keyStore.load(new FileInputStream("signer.p12"), "secret".toCharArray());
        String alias = keyStore.aliases().nextElement();
        PrivateKey privateKey = (PrivateKey) keyStore.getKey(alias, "secret".toCharArray());
        Certificate[] certificateChain = keyStore.getCertificateChain(alias);

        PdfReader reader = new PdfReader("sample.pdf");
        FileOutputStream os = new FileOutputStream("sample-signed.pdf");
        PdfStamper stamper = PdfStamper.createSignature(reader, os, '\0');
        PdfSignatureAppearance appearance = stamper.getSignatureAppearance();
        appearance.setCertificate(certificateChain[0]);

        // This method has to be called as an alternative to 'com.itextpdf.text.pdf.PdfSignatureAppearance.setVisibleSignature'.
        setVisibleSignatureRotated(stamper, appearance, new Rectangle(120, 650, 170, 770), 1, null);

        // Perform the signature.
        ExternalSignature externalSignature = new PrivateKeySignature(privateKey, "SHA-256", null);
        ExternalDigest externalDigest = new BouncyCastleDigest();
        MakeSignature.signDetached(appearance, externalDigest, externalSignature, certificateChain, null, null, null, 0, MakeSignature.CryptoStandard.CMS);
    }

    private static void setVisibleSignatureRotated(PdfStamper stamper, PdfSignatureAppearance appearance, Rectangle pageRect, int page, String fieldName) throws DocumentException, IOException {
        float height = pageRect.getHeight();
        float width = pageRect.getWidth();
        float llx = pageRect.getLeft();
        float lly = pageRect.getBottom();
        // Visual signature is configured as if it were going to be a regular horizontal visual signature.
        appearance.setVisibleSignature(new Rectangle(llx, lly, llx + height, lly + width), page, null);
        // We trigger premature appearance creation, so independent parts of it can be modified right away.
        appearance.getAppearance();
        // Now we correct the width and height.
        appearance.setVisibleSignature(new Rectangle(llx, lly, llx + width, lly + height), page, fieldName);
        appearance.getTopLayer().setWidth(width);
        appearance.getTopLayer().setHeight(height);
        PdfTemplate n2Layer = appearance.getLayer(2);
        n2Layer.setWidth(width);
        n2Layer.setHeight(height);
        // Then we rotate the n2 layer. See http://developers.itextpdf.com/question/how-rotate-paragraph.
        PdfTemplate t = PdfTemplate.createTemplate(stamper.getWriter(), height, width);
        ByteBuffer internalBuffer = t.getInternalBuffer();
        internalBuffer.write(n2Layer.toString().getBytes());
        n2Layer.reset();
        Image textImg = Image.getInstance(t);
        textImg.setInterpolation(true);
        textImg.scaleAbsolute(height, width);
        textImg.setRotationDegrees((float) 90);
        textImg.setAbsolutePosition(0, 0);
        n2Layer.addImage(textImg);
    }
}

如果结果是这样的:

要使用它，您只需按原样复制 setVisibleSignatureRotated 方法，并将对 com.itextpdf.text.pdf.PdfSignatureAppearance#setVisibleSignature 的调用替换为对 setVisibleSignatureRotated。