itext解析pdf中签章文件的证书

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itext可以生成pdf并对其进行各种操作，其中就包括签章，并且用其他工具签的章，itext也可以识别出来。

目前系统中有一个需求，系统要求上传的pdf必须进行签章，上传后需要对pdf进行验签和拿到pdf章的证书的所有者，

拿到章证书的所有者代码如下

	PdfReader reader = new PdfReader(pdfPath);
		AcroFields acroFields = reader.getAcroFields();
		if (acroFields == null) {
			return result;
		}
//签章名称
		List signatureNames = acroFields.getSignatureNames();
		if (signatureNames == null || signatureNames.size() == 0) {
			return result;
		}
		reader.close();
		for (String str : signatureNames) {
//签章对应的字典
			PdfDictionary sigDict = acroFields.getSignatureDictionary(str);
			if (sigDict == null) {
				continue;
			}
			PdfName sub = sigDict.getAsName(PdfName.SUBFILTER);
			if (PdfName.ADBE_X509_RSA_SHA1.equals(sub)) {
//签章对应的证书
				PdfString certStr = sigDict.getAsString(PdfName.CERT);
				if (certStr == null) {
					certStr = sigDict.getAsArray(PdfName.CERT).getAsString(0);
				}
				if (certStr == null) {
					continue;
				}
//签章对应的证书
				X509CertParser certParser = new X509CertParser();
				certParser.engineInit(new ByteArrayInputStream(certStr.getBytes()));
				Collection certs = certParser.engineReadAll();
				if (certs == null || certs.size() == 0) {
					continue;
				}
				X509Certificate certificate = (X509Certificate) certs.iterator().next();
				if (certificate == null) {
					continue;
				}
				X500Principal principal = certificate.getSubjectX500Principal();
				if (principal == null) {
					continue;
				}
//签章对应的证书的所有者
				LdapName ldapDN = new LdapName(principal.getName());
				for (Rdn rdn : ldapDN.getRdns()) {
					if ("CN".equals(rdn.getType())) {
						result.add((String) rdn.getValue());
					}
				}
			}
		}