Retrieve Subject alternative names of X.509 certificate in java

Question

I have tried using the solution provided in this link.

I am getting following error when i tried reading subject alternative names of X.509 Certificate

Answer 1

Many examples use hard-coded integers. For readability, I much prefer to use:

• GeneralName.dNSName = 2
• GeneralName.iPAddress = 7
• ... etc

The code:

public static String[] parseHostNames(X509Certificate cert) {
    List hostNameList = new ArrayList<>();
    try {
        Collection> altNames = cert.getSubjectAlternativeNames();
        if (altNames != null) {
            for(List altName : altNames) {
                if(altName.size()< 2) continue;
                switch((Integer)altName.get(0)) {
                    case GeneralName.dNSName:
                    case GeneralName.iPAddress:
                        Object data = altName.get(1);
                        if (data instanceof String) {
                            hostNameList.add(((String)data));
                        }
                        break;
                    default:
                }
            }
        }
        System.out.println("Parsed hostNames: " + String.join(", ", hostNameList));
    } catch(CertificateParsingException | IOException e) {
        System.err.println("Can't parse hostNames from this cert.");
        e.printStackTrace();
    }
    return hostNameList.toArray(new String[hostNameList.size()]);
}

Note: The accepted answer checks for byte[], but won't compile on my system. I found some other examples using byte[] by calling new ASN1InputStream((byte[])data).readObject();, but I have no certificate to test it with, so I've removed it from my example.