从证书获取公钥

我尝试使用以下方法获取证书的公钥：

I'm trying to obtain the public key of a Certificate using the method:

FileInputStream fin = new FileInputStream("PathToCertificate");
CertificateFactory f = CertificateFactory.getInstance("X.509");
X509Certificate certificate = (X509Certificate)f.generateCertificate(fin);
PublicKey pk = certificate.getPublicKey();

但我收到以下错误：

Exception in thread "main" java.lang.ClassCastException: sun.security.x509.X509CertImpl cannot be cast to codec.x509.X509Certificate
        at sergas_testcertificates.Main.main(Main.java:54)

有人知道这个错误是什么吗？

Does anyone know what this error is about?

提前感谢