I have the following bountycastle code and I need to switch it to use plain java only:

private PrivateKey getPrivateKeyFromCertificate(String certificate) throws Exception {
    PEMParser parser = new PEMParser(new StringReader(certificate));
    return new JcaPEMKeyConverter().getPrivateKey((PrivateKeyInfo) parser.readObject());
}

I tried this:

private PrivateKey getPrivateKeyFromCertificate(String certificate) throws Exception {
    String pemBase64 = certificate
            .replace("-----BEGIN PRIVATE KEY-----", "")
            .replaceAll("\r", "")
            .replaceAll("\n", "")
            .replace("-----END PRIVATE KEY-----", ""));
    byte[] pemData = Base64.decodeBase64(pemBase64);
    KeyFactory keyFactory = KeyFactory.getInstance("RSA");
    PrivateKey privateKey = keyFactory.generatePrivate(new PKCS8EncodedKeySpec(pemData));
    return privateKey;
}

But I get the following error: java.security.spec.InvalidKeySpecException: java.security.InvalidKeyException: Invalid RSA private key