ContentHandlerBase64Encoder.java

/*
 * Copyright 2005-2015 by BerryWorks Software, LLC. All rights reserved.
 *
 * This file is part of EDIReader. You may obtain a license for its use directly from
 * BerryWorks Software, and you may also choose to use this software under the terms of the
 * GPL version 3. Other products in the EDIReader software suite are available only by licensing
 * with BerryWorks. Only those files bearing the GPL statement below are available under the GPL.
 *
 * EDIReader is free software: you can redistribute it and/or modify it under the terms of the
 * GNU General Public License as published by the Free Software Foundation, either version 3 of
 * the License, or (at your option) any later version.
 *
 * EDIReader is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without
 * even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along with EDIReader.  If not,
 * see <http://www.gnu.org/licenses/>.
 */

package com.berryworks.edireader.util;

import com.berryworks.edireader.util.base64.AbstractEncoder;
import org.xml.sax.ContentHandler;
import org.xml.sax.SAXException;

import java.nio.ByteBuffer;
import java.nio.CharBuffer;
import java.nio.charset.CharsetEncoder;
import java.nio.charset.CoderResult;

/**
 * Encode char data using base-64 conventions
 * before presenting that data to a SAX ContentHandler.
 */
public class ContentHandlerBase64Encoder extends AbstractEncoder {

    private ContentHandler contentHandler;
    private ByteBuffer base64Bytes;

    public void encode(char[] dataObject, ContentHandler contentHandler) {
        this.contentHandler = contentHandler;
        CharBuffer charBuffer = CharBuffer.wrap(dataObject);

        // Allocate a modest sized non-direct ByteBuffer to receive the
        // bytes as they are encoded from the chars
        ByteBuffer byteBuffer = ByteBuffer.allocate(100);

        // Allocate a similar ByteBuffer to receive the bytes as they are emitted
        // by the Base 64 encoder.
        base64Bytes = ByteBuffer.allocate(100);

        // Use an encoder repeatedly until all of the chars have been encoded as bytes
        // and presented as input for base 64 encoding.
        CharsetEncoder encoder = charset.newEncoder();
        while (true) {
            CoderResult coderResult = encoder.encode(charBuffer, byteBuffer, true);
            if (coderResult.isError())
                throw new RuntimeException("Unrecoverable failure in Base64 encoding");
            byteBuffer.flip();
            while (byteBuffer.hasRemaining())
                consume(byteBuffer.get());
            if (coderResult.isUnderflow()) break;
            byteBuffer.clear();
        }
        endOfData();
        feedContentHandler();
    }

    @Override
    protected void emit(byte b) {

        if (!base64Bytes.hasRemaining()) {
            // Whenever the ByteBuffer gets full, use the CharSetEncoder
            // to turn the bytes into chars in a CharBuffer.
            // Whenever the CharBuffer gets full, give those chars
            // to the SAX ContentHandler.
            feedContentHandler();
            base64Bytes.clear();
        }
        // Put the byte into a byteBuffer.
        base64Bytes.put(b);
    }

    private void feedContentHandler() {
        base64Bytes.flip();
        CharBuffer charBuffer = charset.decode(base64Bytes);
        try {
            contentHandler.characters(charBuffer.array(), 0, charBuffer.length());
        } catch (SAXException e) {
            throw new RuntimeException("Unrecoverable failure in Base64 encoding");
        }
    }

}