Java校验.CER、.pem证书格式以及获取证书有效期

public static void main(String[] args) throws CertificateException, FileNotFoundException {
        CertificateFactory cf = CertificateFactory.getInstance("X.509");
        FileInputStream in = new  FileInputStream("/Users/name/Downloads/cert.pem");
        X509Certificate cert = (X509Certificate) cf.generateCertificate(in);
        cert.checkValidity();    //校验格式，错误抛出异常，可捕捉
        Date effDate = cert.getNotBefore();
        Date expDate = cert.getNotAfter();
        long diff = expDate.getTime() - effDate.getTime();
        System.out.println(diff / (1000 * 60 * 60 * 24));
        System.out.println(effDate);
        System.out.println(expDate);
    }