gistfile1.java

The signing implementation
The SignImp class isn’t much different from all the examples we’ve written before. When I write 
Servlets that involve the use of iText, I always start by writing a short standalone application with a 
main() method. This way I can test the code before integrating it into a web application.
In code sample 4.11, I’ve removed the main() method for brevity.
Code sample 4.11: the SignImp class
public class SignImp {
 private PrivateKey pk;
 private Certificate[] chain;
 public SignImp(PrivateKey pk, Certificate[] chain) {
 this.pk = pk;
 this.chain = chain;
 }
 public byte[] signDoc(InputStream pdf, String reason, String location)
 throws GeneralSecurityException, IOException, DocumentException {
 // Creating the reader and the stamper
 PdfReader reader = new PdfReader(pdf, null);
 ByteArrayOutputStream baos = new ByteArrayOutputStream();
 PdfStamper stamper =
 PdfStamper.createSignature(reader, baos, '\0', null, true);
 // Creating the appearance
 PdfSignatureAppearance appearance = stamper.getSignatureAppearance();
 appearance.setReason(reason);
 appearance.setLocation(location);
 // Creating the signature
 ExternalSignature pks =
 new PrivateKeySignature(pk, DigestAlgorithms.SHA256, null);
 ExternalDigest digest = new BouncyCastleDigest();
 MakeSignature.signDetached(appearance, digest, pks, chain,
 null, null, null, 0, CryptoStandard.CMS);
 return baos.toByteArray();
 }
}