if (doc.getFirstChild() != null) {

                doc.getFirstChild().appendChild(sig.getElement());
                Transforms transforms = new Transforms(doc);
                transforms.addTransform("http://www.w3.org/2000/09/xmldsig#enveloped-signature");
                transforms.addTransform("http://www.w3.org/TR/2001/REC-xml-c14n-20010315#WithComments");
                //transforms.addTransform("http://www.w3.org/2001/10/xml-exc-c14n#WithComments");
                sig.addDocument("", transforms, digestMethod); //while document
               // sig.addDocument("#"+"test", transforms, digestMethod);
                sig.addKeyInfo((X509Certificate) cert);
                sig.sign(privateKey);