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.cms;

import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.io.InputStream;

import org.bouncycastle.asn1.ASN1Encodable;
import org.bouncycastle.asn1.ASN1Encoding;
import org.bouncycastle.asn1.ASN1ObjectIdentifier;

public class PKCS7TypedStream
    extends CMSTypedStream
{
    private final ASN1Encodable content;

    public PKCS7TypedStream(ASN1ObjectIdentifier oid, ASN1Encodable encodable)
        throws IOException
    {
        super(oid);

        content = encodable;
    }

    public ASN1Encodable getContent()
    {
        return content;
    }

    public InputStream getContentStream()
    {
        try
        {
            return getContentStream(content);
        }
        catch (IOException e)
        {
            throw new CMSRuntimeException("unable to convert content to stream: " + e.getMessage(), e);
        }
    }

    public void drain()
        throws IOException
    {
        getContentStream(content); // this will parse in the data
    }

    private InputStream getContentStream(ASN1Encodable encodable)
        throws IOException
    {
        byte[] encoded = encodable.toASN1Primitive().getEncoded(ASN1Encoding.DER);
        int index = 1;

        while ((encoded[index] & 0xff) > 127)
        {
            index++;
        }

        index++;

        return new ByteArrayInputStream(encoded, index, encoded.length - index);
    }
}