无法从给定的输入流获取certPath obj

Question

如何在下面的代码中获取编码类型为PKI_PATH的certPath obj（输入证书以字符串形式）

CertificateFactory fact = CertificateFactory.getInstance("X.509");
InputStream stream = new 
ByteArrayInputStream(certificateString.trim().getBytes());
CertPath certPath = fact.generateCertPath(stream, "PkiPath");