I had some historical key material data in pkcs#1 format that needed to be in pkcs#8 for input into another system. Here's how to do it, using BouncyCastle:
import org.bouncycastle.asn1.ASN1InputStream;
import org.bouncycastle.asn1.DERObject;
import org.bouncycastle.asn1.pkcs.PKCSObjectIdentifiers;
import org.bouncycastle.asn1.pkcs.PrivateKeyInfo;
import org.bouncycastle.asn1.x509.AlgorithmIdentifier;
import java.security.PrivateKey;