keyStore.getKey() returns NULL - certificate

Question

I want to sign a PDF with a self generated certificate. In this process I need a keystore and private key. The signing will be made with PDFBox by using the class CreateSignature()
To generate a keyStore with a self generated certificate I am using this:
public KeyStore generateSampleKeyStoreWith509Certificate() throws KeyStoreException, NoSuchAlgorithmException,
CertificateException, IOException, UnrecoverableEntryException {
X509Certificate cert;
PrivateKey caKey;
try {
KeyPairGenerator keyPairGenerator = KeyPairGenerator.getInstance("RSA", "BC");
keyPairGenerator.initialize(1024, new SecureRandom());
KeyPair keyPair = keyPairGenerator.generateKeyPair();
caKey = keyPair.getPrivate();
Date notBefore = new Date();
Date notAfter = new Date(System.currentTimeMillis() + 1000 * 60 * 60 * 24 * 365);
SubjectPublicKeyInfo spkInfo = SubjectPublicKeyInfo.getInstance(keyPair.getPublic().getEncoded());
X509v3CertificateBuilder newGen = new X509v3CertificateBuilder(new X500Name(issuer), serial, notBefore,
notAfter, new X500Name(subject), spkInfo);
ContentSigner sigGen = new JcaContentSignerBuilder("SHA256WithRSAEncryption").setProvider("BC")
.build(caKey);
X509CertificateHolder certHolder = newGen.build(sigGen);
CertificateFactory cf = CertificateFactory.getInstance("X.509");
InputStream is1 = new ByteArrayInputStream(certHolder.getEncoded());
cert = (X509Certificate) cf.generateCertificate(is1);
is1.close();
} catch (OperatorCreationException | CertificateException | IOException | NoSuchProviderException
| NoSuchAlgorithmException e) {
throw new RuntimeException(e);
}
KeyStore keyStore = KeyStore.getInstance(KeyStore.getDefaultType());
keyStore.load(null, password);
keyStore.setCertificateEntry("SelfSigned", cert);
return keyStore;
}
The certificate is entered correctly, but shouldn't there be a key, too? Or am I wrong that the keystore should be holding a key?
I'm just figuring this sibject, so I'm thankful of every bit of help.

Answer 1

X509Certificate[] certChain = new X509Certificate[1];
certChain[0] = cert;
keyStore.setKeyEntry("SelfSigned",caKey, password, certChain);
Adding the above code, at the bottom, enters the privateKey previously created to the keystore. It seems most examples on the internet assume loading a keystore with privatekey already entered before.