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jBasics is a collection of useful utility classes for Java. This includes helper for XML, mathematic functions, restful web services helper, pattern oriented programming interfaces and more. Currently Java7 and up is supported. Version 1.0 will required at leaset Java8.
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/*
 * Copyright (c) 2009-2015
 * 	IT-Consulting Stephan Schloepke (http://www.schloepke.de/)
 * 	klemm software consulting Mirko Klemm (http://www.klemm-scs.com/)
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */
package org.jbasics.codec;

import org.jbasics.arrays.ArrayConstants;
import org.jbasics.pattern.coder.Codec;
import org.jbasics.text.StringUtilities;

import java.io.ByteArrayOutputStream;

/**
 * Codec for the RFC3548 base 16 coding. This is one of the three codecs defined in the RFC3548. The codec is also known
 * as the hex codec because it results. in two character hex values for one byte.
 *
 * @author Stephan Schloepke
 * @since 1.0
 */
public class RFC3548Base64Codec implements Codec {
	public static final String BASE64_ALPHABET = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"; //$NON-NLS-1$
	public static final String BASE64_ALPHABET_ALT = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_"; //$NON-NLS-1$
	public static final char PADDING_CHARACTER = '=';

	public static final RFC3548Base64Codec INSTANCE = new RFC3548Base64Codec();
	public static final RFC3548Base64Codec INSTANCE_ALT = new RFC3548Base64Codec(true);

	private final String alphabet;
	private final boolean fillWithoutPadding;

	public RFC3548Base64Codec() {
		this(false, false);
	}

	public RFC3548Base64Codec(final boolean alternate, final boolean fillWithoutPadding) {
		this.alphabet = alternate ? RFC3548Base64Codec.BASE64_ALPHABET_ALT : RFC3548Base64Codec.BASE64_ALPHABET;
		this.fillWithoutPadding = fillWithoutPadding;
	}

	public RFC3548Base64Codec(final boolean alternate) {
		this(alternate, false);
	}

	/**
	 * Returns the input block size used for encoding.
	 *
	 * @return The input block size
	 */
	public int getInputBlockSize() {
		return 3;
	}

	/**
	 * Returns the output block size used for encoding
	 *
	 * @return The output block size
	 */
	public int getOutputBlockSize() {
		return 4;
	}

	@Override
	public CharSequence encode(final byte[] input) {
		if (input == null || input.length == 0) {
			return StringUtilities.EMPTY_STRING;
		}
		final int lastBlockSize = input.length % 3;
		final int fullBlocks = input.length / 3;
		final StringBuilder builder = new StringBuilder();
		for (int z = fullBlocks, i = 0; z > 0; z--, i += 3) {
			final int temp = (input[i] & 0xff) << 16 | (input[i + 1] & 0xff) << 8 | input[i + 2] & 0xff;
			int p = 18;
			for (int j = 0; j < 4; j++) {
				builder.append(this.alphabet.charAt(temp >>> p & 0x3f));
				p -= 6;
			}
		}
		if (lastBlockSize > 0) {
			int j = 3;
			long temp = 0;
			for (int i = input.length - lastBlockSize; i < input.length; i++, j--) {
				temp = temp << 8 | input[i] & 0xff;
			}
			for (; j > 0; j--) {
				temp <<= 8;
			}
			if (this.fillWithoutPadding) {
				int p = 18;
				for (int i = 0; i < 8; i++) {
					builder.append(this.alphabet.charAt((int) (temp >>> p & 0x3f)));
					p -= 6;
				}
			} else {
				int p = 18;
				for (int i = (lastBlockSize * 8 + 5) / 6; i > 0; i--) {
					builder.append(this.alphabet.charAt((int) (temp >>> p & 0x3f)));
					p -= 6;
				}
				for (int i = 4 - (lastBlockSize * 8 + 5) / 6; i > 0; i--) {
					builder.append(RFC3548Base64Codec.PADDING_CHARACTER);
				}
			}
		}
		return builder.toString();
	}

	@Override
	public byte[] decode(final CharSequence input) {
		if (input == null || input.length() == 0) {
			return ArrayConstants.ZERO_LENGTH_BYTE_ARRAY;
		}
		final ByteArrayOutputStream data = new ByteArrayOutputStream(input.length() * 3 / 4);
		int pos = 0;
		int value = 0;
		int padding = 0;
		for (int i = 0; i < input.length(); i++) {
			final char c = input.charAt(i);
			int p = 0;
			if (c == RFC3548Base64Codec.PADDING_CHARACTER) {
				padding++;
			} else {
				p = this.alphabet.indexOf(c);
			}
			if (p < 0) {
				continue;
			}
			value = value << 6 | p;
			pos = (pos + 1) % 4;
			if (pos == 0) {
				if (padding == 0) {
					data.write((byte) (value >>> 16));
					data.write((byte) (value >>> 8));
					data.write((byte) (value & 0xff));
				} else {
					data.write((byte) (value >>> 16));
					if (padding == 1) {
						data.write((byte) (value >>> 8));
					}
				}
			}
		}
		// Missing fail safe if the input is not a multiple of 4 (discarding all non part characters)
		return data.toByteArray();
	}
}