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.encoding;

import java.io.FilterOutputStream;
import java.io.IOException;
import java.io.OutputStream;

import org.bouncycastle.util.encoders.Base64;

public class Base64OutputStream
    extends FilterOutputStream
{
    byte[] buffer = new byte[54];
    int    bufOff;

    public Base64OutputStream(OutputStream stream)
    {
        super(stream);
    }

    public void write(int b)
        throws IOException
    {
        doWrite((byte)b);
    }

    public void write(byte[] buf, int bufOff, int len)
        throws IOException
    {
        for (int i = 0; i != len; i++)
        {
            doWrite(buf[bufOff + i]);
        }
    }

    public void write(byte[] buf)
        throws IOException
    {
        write(buf, 0, buf.length);
    }

    public void close()
        throws IOException
    {
        if (bufOff > 0)
        {
            Base64.encode(buffer, 0, bufOff, out);
        }
        out.close();
    }
    
    private void doWrite(byte b)
        throws IOException
    {
        buffer[bufOff++] = b;
        if (bufOff == buffer.length)
        {
            Base64.encode(buffer, 0, buffer.length, out);
            out.write('\r');
            out.write('\n');
            bufOff = 0;
        }
    }
}