$ openssl x509 -in 1900009191_20180326_cert.pem -noout -serial
serial=1DDE55AD98ED71D6EDD4A4A16996DE7B47773A8C

/**
 * 獲取證書。
 *
 * @param filename 證書文件路徑  (required)
 * @return X509證書
 */
public static X509Certificate getCertificate(String filename) throws IOException {
	InputStream fis = new FileInputStream(filename);
	BufferedInputStream bis = new BufferedInputStream(fis);

	try {
		CertificateFactory cf = CertificateFactory.getInstance("X509");
		X509Certificate cert = (X509Certificate) cf.generateCertificate(bis);
		cert.checkValidity();
		return cert;
	} catch (CertificateExpiredException e) {
		throw new RuntimeException("證書已過期", e);
	} catch (CertificateNotYetValidException e) {
		throw new RuntimeException("證書尚未生效", e);
	} catch (CertificateException e) {
		throw new RuntimeException("無效的證書文件", e);
	} finally {
		bis.close();
	}
}

 
/**
* Read certificate from file
*
* @param string    $filepath     PEM encoded X.509 certificate file path
* 
* @return resource|bool  X.509 certificate resource identifier on success or FALSE on failure
*/
public static function getCertificate($filepath) {
    return openssl_x509_read(file_get_contents($filepath));}