java 数字证书信息的获取实例 java学习笔记(2)

用java提供的api实现从证书文件(本实例实验对象为*.cer文件)中获取有效信息的方法..
public static X509Certificate getCert(String fileName) throws Exception {//从一个有效的证书文件来创建证书..
InputStream inStream = new FileInputStream(fileName);
CertificateFactory cf = CertificateFactory.getInstance("X.509");//用证书工厂来创建证书..
X509Certificate cert = (X509Certificate)cf.generateCertificate(inStream);
inStream.close();
return cert;
}
public static void showCert( X509Certificate cert ) {//输出证书的各项信息..
System.out.println("Version: " + cert.getVersion());//证书版本..
System.out.println("SerialNumber: " + cert.getSerialNumber().toString(16) );//证书序列号..
System.out.println("SignatureAlgorithm: " + cert.getSigAlgName());//证书签名算法..
X500Principal principal = cert.getIssuerX500Principal();
System.out.println("IssuerName: \n" + principal.getName(X500Principal.RFC1779));//证书颁发者
//System.out.println(principal.hashCode());
GregorianCalendar gcal = new GregorianCalendar();
System.out.print("Validityfrom: ");
gcal.setTime(cert.getNotBefore());//证书有效期从..
System.out.println(gcal.get(GregorianCalendar.YEAR)+"/"+gcal.get(GregorianCalendar.MONTH)+"/"+gcal.get(GregorianCalendar.DAY_OF_MONTH)+" "+gcal.get(GregorianCalendar.HOUR_OF_DAY)+":"+gcal.get(GregorianCalendar.MINUTE)+":"+gcal.get(GregorianCalendar.SECOND));
System.out.print("ValidityTo: ");
gcal.setTime(cert.getNotAfter());//证书有效期到..
System.out.println(gcal.get(GregorianCalendar.YEAR)+"/"+gcal.get(GregorianCalendar.MONTH)+"/"+gcal.get(GregorianCalendar.DAY_OF_MONTH)+" "+gcal.get(GregorianCalendar.HOUR_OF_DAY)+":"+gcal.get(GregorianCalendar.MINUTE)+":"+gcal.get(GregorianCalendar.SECOND));
principal = cert.getSubjectX500Principal();
System.out.println("SubjectName: \n" + principal.getName(X500Principal.RFC1779));//证书使用者
PublicKey pkey = cert.getPublicKey();//获得公钥