java实现印章签名

要实现 Java 中的印章签名，可以使用数字证书和印章图片。具体操作步骤如下：

1. 获取数字证书和私钥，并使用私钥对印章图片进行签名。可以使用 Java 中的 KeyStore 类和 PrivateKey 接口来获取证书和私钥。

   KeyStore keyStore = KeyStore.getInstance("PKCS12");
   keyStore.load(new FileInputStream("path/to/certificate.pfx"), "password".toCharArray());
   
   String alias = keyStore.aliases().nextElement();
   X509Certificate cert = (X509Certificate) keyStore.getCertificate(alias);
   PrivateKey privateKey = (PrivateKey) keyStore.getKey(alias, "password".toCharArray());
   
   BufferedImage stamp = ImageIO.read(new FileInputStream("path/to/stamp.png"));
   Signature signature = Signature.getInstance("SHA256withRSA");
   signature.initSign(privateKey);
   
   ByteArrayOutputStream stampBytes = new ByteArrayOutputStream();
   ImageIO.write(stamp, "png", stampBytes);
   byte[] stampData = stampBytes.toByteArray();
   
   signature.update(stampData);
   byte[] signedData = signature.sign();

2. 将签名后的印章图片和证书一起写入 PDF 文件中。可以使用 iText 库来操作 PDF 文件。

   PdfReader reader = new PdfReader("path/to/unsigned.pdf");
   PdfStamper stamper = new PdfStamper(reader, new FileOutputStream("path/to/signed.pdf"));
   
   PdfSignatureAppearance appearance = stamper.getSignatureAppearance();
   appearance.setReason("I am the author");
   appearance.setLocation("Beijing");
   appearance.setVisibleSignature(new Rectangle(100, 100, 200, 200), 1, "signature");
   
   PdfTemplate template = PdfTemplate.createTemplate(stamper.getWriter(), stamp.getWidth(), stamp.getHeight());
   Graphics2D g2d = template.createGraphics(stamp.getWidth(), stamp.getHeight());
   g2d.drawImage(stamp, 0, 0, null);
   g2d.dispose();
   
   PdfImage image = PdfImage.getImage(template);
   appearance.setImage(image);
   
   ExternalSignature pks = new PrivateKeySignature(privateKey, "SHA-256", "BC");
   ExternalDigest digest = new BouncyCastleDigest();
   
   MakeSignature.signDetached(appearance, digest, pks, new X509Certificate[]{cert}, null, null, null, 0, MakeSignature.CryptoStandard.CMS);
   
   stamper.close();
   reader.close();

以上就是 Java 实现印章签名的基本步骤。需要注意的是，本例中使用了 BouncyCastle 库来实现签名算法，需要预先引入该库。