在Android Project上找不到认证路径的信任锚

InputStream caInput = getResources().openRawResource(R.raw.server_cert);
CertificateFactory certificateFactory = CertificateFactory.getInstance("X.509");
Certificate ca = certificateFactory.generateCertificate(caInput);

// Create a KeyStore containing the trusted CA
KeyStore keyStore = KeyStore.getInstance(KeyStore.getDefaultType());
keyStore.load(null, null);
keyStore.setCertificateEntry("ca", ca);

// Create a TrustManager that trusts the CA in the KeyStore
TrustManagerFactory trustManagerFactory = TrustManagerFactory.getInstance(TrustManagerFactory.getDefaultAlgorithm());
trustManagerFactory.init(keyStore);

// Create an SSLContext with the TrustManager
SSLContext sslContext = SSLContext.getInstance("TLS");
sslContext.init(null, trustManagerFactory.getTrustManagers(), null);

// Set the SSLContext on the OkHttpClient
OkHttpClient client = new OkHttpClient.Builder().sslSocketFactory(sslContext.getSocketFactory()).build();