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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 32 coding. This is one of the three codecs defined in the RFC3548.
 *
 * @author Stephan Schloepke
 * @since 1.0
 */
public class RFC3548Base32Codec implements Codec {
	/**
	 * The alphabet used in the encoding and decoding process in upper case letters (case does not matter)
	 *
	 * @since 1.0
	 */
	public static final String BASE32_ALPHABET = "ABCDEFGHIJKLMNOPQRSTUVWXYZ01234567"; //$NON-NLS-1$
	/**
	 * The padding character used to fill the remaining characters to fit into the output block size
	 *
	 * @since 1.0
	 */
	public static final char PADDING_CHARACTER = '=';
	/**
	 * The shared instance to use (with padding in the result).
	 *
	 * @since 1.0
	 */
	public static final RFC3548Base32Codec INSTANCE = new RFC3548Base32Codec();
	private final boolean fillWithoutPadding;

	/**
	 * Creates the standard codec with padding to fill the result.
	 *
	 * @since 1.0
	 */
	public RFC3548Base32Codec() {
		this(false);
	}

	/**
	 * Creates the codec with the option to not use the default padding to fill the blocks.
	 *
	 * @param fillWithoutPadding true to switch off the padding of the result blocks.
	 *
	 * @since 1.0
	 */
	public RFC3548Base32Codec(final boolean fillWithoutPadding) {
		this.fillWithoutPadding = fillWithoutPadding;
	}

	/**
	 * Returns the input block size used for encoding.
	 *
	 * @return The input block size
	 *
	 * @since 1.0
	 */
	public int getInputBlockSize() {
		return 5;
	}

	/**
	 * Returns the output block size used for encoding
	 *
	 * @return The output block size
	 *
	 * @since 1.0
	 */
	public int getOutputBlockSize() {
		return 8;
	}

	/*
	 * (non-Javadoc)
	 * 
	 * @see org.jbasics.pattern.coder.Encoder#encode(java.lang.Object)
	 */
	@Override
	public CharSequence encode(final byte[] input) {
		if (input == null || input.length == 0) {
			return StringUtilities.EMPTY_STRING;
		}
		final int lastBlockSize = input.length % 5;
		final int fullBlocks = input.length / 5;
		final StringBuilder builder = new StringBuilder();
		for (int z = fullBlocks, i = 0; z > 0; z--, i += 5) {
			final long temp = (long) (input[i] & 0xff) << 32 | (input[i + 1] & 0xff) << 24 | (input[i + 2] & 0xff) << 16 | (input[i + 3] & 0xff) << 8
					| input[i + 4] & 0xff;
			int p = 35;
			for (int j = 0; j < 8; j++) {
				builder.append(RFC3548Base32Codec.BASE32_ALPHABET.charAt((int) (temp >>> p & 0x1f)));
				p -= 5;
			}
		}
		if (lastBlockSize > 0) {
			int j = 5;
			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 = 35;
				for (int i = 0; i < 8; i++) {
					builder.append(RFC3548Base32Codec.BASE32_ALPHABET.charAt((int) (temp >>> p & 0x1f)));
					p -= 5;
				}
			} else {
				int p = 35;
				for (int i = (lastBlockSize * 8 + 4) / 5; i > 0; i--) {
					builder.append(RFC3548Base32Codec.BASE32_ALPHABET.charAt((int) (temp >>> p & 0x1f)));
					p -= 5;
				}
				for (int i = 8 - (lastBlockSize * 8 + 4) / 5; i > 0; i--) {
					builder.append(RFC3548Base32Codec.PADDING_CHARACTER);
				}
			}
		}
		return builder.toString();
	}

	/*
	 * (non-Javadoc)
	 * 
	 * @see org.jbasics.pattern.coder.Decoder#decode(java.lang.Object)
	 */
	@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() * 5 / 8);
		int pos = 0;
		long value = 0;
		int padding = 0;
		for (int i = 0; i < input.length(); i++) {
			final char c = Character.toUpperCase(input.charAt(i));
			int p = 0;
			if (c == RFC3548Base32Codec.PADDING_CHARACTER) {
				padding++;
			} else {
				p = RFC3548Base32Codec.BASE32_ALPHABET.indexOf(c);
			}
			if (p < 0) {
				continue;
			}
			value = value << 5 | p;
			pos = (pos + 1) % 8;
			if (pos == 0) {
				writeDecoded(data, value, padding);
			}
		}
		// Missing fail safe if the input is not a multiple of 8 (discarding all non part characters)
		return data.toByteArray();
	}

	private void writeDecoded(final ByteArrayOutputStream data, final long value, final int padding) {
		if (padding == 0) {
			data.write((byte) (value >>> 32));
			data.write((byte) (value >>> 24));
			data.write((byte) (value >>> 16));
			data.write((byte) (value >>> 8));
			data.write((byte) (value & 0xff));
		} else {
			data.write((byte) (value >>> 32));
			if (padding < 5) {
				data.write((byte) (value >>> 24));
				if (padding < 4) {
					data.write((byte) (value >>> 16));
					if (padding < 2) {
						data.write((byte) (value >>> 8));
					}
				}
			}
		}
	}
}