Construct secure networked applications with certificates, Part 2

import java.util.Set;
import java.util.Iterator;
import java.io.FileInputStream;
import java.security.cert.CertificateFactory;
import java.security.cert.X509Certificate;
public
class Main
{
  public
  static
  void
  main(String [] arstring)
  {
    try
    {
      // Get the correct certificate factory.
      CertificateFactory certificatefactory = CertificateFactory.getInstance("X.509");
      // Each file specified on the command line must contain a single
      // DER-encoded X.509 certificate.  The DER-encoded certificate
      // can be in either binary or ASCII format.
      for (int i = 0; i < arstring.length; i++)
      {
        // Open the file.
        FileInputStream fileinputstream = new FileInputStream(arstring[i]);
        // Generate a certificate from the data in the file.
        X509Certificate x509certificate =
          (X509Certificate)certificatefactory.generateCertificate(fileinputstream);
        // First, let's print out information about the certificate itself.
        System.out.println("---Certificate---");
        System.out.println("type = " + x509certificate.getType());
        System.out.println("version = " + x509certificate.getVersion());
        System.out.println("subject = " + x509certificate.getSubjectDN().getName());
        System.out.println("valid from = " + x509certificate.getNotBefore());
        System.out.println("valid to = " + x509certificate.getNotAfter());
        System.out.println("serial number = " + x509certificate.getSerialNumber().toString(16));
        System.out.println("issuer = " + x509certificate.getIssuerDN().getName());
        System.out.println("signing algorithm = " + x509certificate.getSigAlgName());
        System.out.println("public key algorithm = " + x509certificate.getPublicKey().getAlgorithm());
        // Next, let's print out information about the extensions.
        System.out.println("---Extensions---");
        Set setCritical = x509certificate.getCriticalExtensionOIDs();
        if (setCritical != null && setCritical.isEmpty() == false)
          for (Iterator iterator = setCritical.iterator(); iterator.hasNext(); )
            System.out.println(iterator.next().toString() + " *critical*");
        Set setNonCritical = x509certificate.getNonCriticalExtensionOIDs();
        if (setNonCritical != null && setNonCritical.isEmpty() == false)
          for (Iterator iterator = setNonCritical.iterator(); iterator.hasNext(); )
            System.out.println(iterator.next().toString());
        // We're done.
        System.out.println("---");
        // Close the file.
        fileinputstream.close();
      }
    }
    catch (Exception exception)
    {
      exception.printStackTrace();
    }
  }
}