http://www.bouncycastle.org/java.html: The Bouncy Castle Java APIs for CMS, PKCS, EAC, TSP, CMP, CRMF, OCSP, and certificate generation. This jar contains APIs for JDK 1.5 to JDK 1.8. The APIs can be used in conjunction with a JCE/JCA provider such as the one provided with the Bouncy Castle Cryptography APIs.
  • The Legion of the Bouncy Castle Inc. 
package org.bouncycastle.openssl.jcajce;

import java.security.PrivateKey;

import org.bouncycastle.asn1.pkcs.PrivateKeyInfo;
import org.bouncycastle.openssl.PKCS8Generator;
import org.bouncycastle.operator.OutputEncryptor;
import org.bouncycastle.util.io.pem.PemGenerationException;

public class JcaPKCS8Generator
    extends PKCS8Generator
{
    public JcaPKCS8Generator(PrivateKey key, OutputEncryptor encryptor)
         throws PemGenerationException
    {
         super(PrivateKeyInfo.getInstance(key.getEncoded()), encryptor);
    }
}