http://www.bouncycastle.org/java.html: The Bouncy Castle Crypto package is a Java implementation of cryptographic algorithms. This jar contains JCE provider and lightweight API for the Bouncy Castle Cryptography APIs for JDK 1.5 to JDK 1.8.
  • The Legion of the Bouncy Castle Inc. 
package org.bouncycastle.crypto.params;

import java.math.BigInteger;

public class ECPrivateKeyParameters
    extends ECKeyParameters
{
    BigInteger d;

    public ECPrivateKeyParameters(
        BigInteger          d,
        ECDomainParameters  params)
    {
        super(true, params);
        this.d = d;
    }

    public BigInteger getD()
    {
        return d;
    }
}