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.mime;

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

public class ConstantMimeContext
    implements MimeContext, MimeMultipartContext
{
    public InputStream applyContext(Headers headers, InputStream contentStream)
        throws IOException
    {
        return contentStream;
    }

    public MimeContext createContext(int partNo)
        throws IOException
    {
        return this;
    }
}