Base64.java

package jqian.util;

/**
 * Provides encoding of raw bytes to base64-encoded characters, and decoding of
 * base64 characters to raw bytes.
 * 
 * @author Kevin Kelley (kelley@ruralnet.net)
 * @version 1.3
 * @date 06 August 1998
 * @modified 14 February 2000
 * @modified 22 September 2000
 */
public class Base64 {

	/**
	 * returns an array of base64-encoded characters to represent the passed
	 * data array.
	 * 
	 * @param data
	 *            the array of bytes to encode
	 * @return base64-coded character array.
	 */
	static public char[] encode(byte[] data) {
		char[] out = new char[((data.length + 2) / 3) * 4];

//
// 3 bytes encode to 4 chars. Output is always an even
// multiple of 4 characters.
//
		for (int i = 0, index = 0; i < data.length; i += 3, index += 4) {
			boolean quad = false;
			boolean trip = false;

			int val = (0xFF & data[i]);
			val <<= 8;
			if ((i + 1) < data.length) {
				val |= (0xFF & data[i + 1]);
				trip = true;
			}
			val <<= 8;
			if ((i + 2) < data.length) {
				val |= (0xFF & data[i + 2]);
				quad = true;
			}
			out[index + 3] = alphabet[(quad ? (val & 0x3F) : 64)];
			val >>= 6;
			out[index + 2] = alphabet[(trip ? (val & 0x3F) : 64)];
			val >>= 6;
			out[index + 1] = alphabet[val & 0x3F];
			val >>= 6;
			out[index + 0] = alphabet[val & 0x3F];
		}
		return out;
	}

	/**
	 * Decodes a BASE-64 encoded stream to recover the original data. White
	 * space before and after will be trimmed away, but no other manipulation of
	 * the input will be performed.
	 * 
	 * As of version 1.2 this method will properly handle input containing junk
	 * characters (newlines and the like) rather than throwing an error. It does
	 * this by pre-parsing the input and generating from that a count of VALID
	 * input characters.
	 */
	static public byte[] decode(char[] data) {
// as our input could contain non-BASE64 data (newlines,
// whitespace of any sort, whatever) we must first adjust
// our count of USABLE data so that...
// (a) we don't misallocate the output array, and
// (b) think that we miscalculated our data length
// just because of extraneous throw-away junk

		int tempLen = data.length;
		for (char element : data) {
			if ((element > 255) || codes[element] < 0)
				--tempLen; // ignore non-valid chars and padding
		}
// calculate required length:
// -- 3 bytes for every 4 valid base64 chars
// -- plus 2 bytes if there are 3 extra base64 chars,
// or plus 1 byte if there are 2 extra.

		int len = (tempLen / 4) * 3;
		if ((tempLen % 4) == 3)
			len += 2;
		if ((tempLen % 4) == 2)
			len += 1;

		byte[] out = new byte[len];

		int shift = 0; // # of excess bits stored in accum
		int accum = 0; // excess bits
		int index = 0;

		for (char element : data) {
			int value = (element > 255) ? -1 : codes[element];

			if (value >= 0) // skip over non-code
			{
				accum <<= 6; // bits shift up by 6 each time thru
				shift += 6; // loop, with new bits being put in
				accum |= value; // at the bottom.
				if (shift >= 8) // whenever there are 8 or more shifted in,
				{
					shift -= 8; // write them out (from the top, leaving any
					out[index++] = // excess at the bottom for next iteration.
					(byte) ((accum >> shift) & 0xff);
				}
			}
// we will also have skipped processing a padding null byte ('=') here;
// these are used ONLY for padding to an even length and do not legally
// occur as encoded data. for this reason we can ignore the fact that
// no index++ operation occurs in that special case: the out[] array is
// initialized to all-zero bytes to start with and that works to our
// advantage in this combination.
		}

// if there is STILL something wrong we just have to throw up now!
		if (index != out.length) {
			throw new Error("Miscalculated data length (wrote " + index
					+ " instead of " + out.length + ")");
		}

		return out;
	}

//
// code characters for values 0..63
//
	private static final char[] alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/="
			.toCharArray();

//
// lookup table for converting base64 characters to value in range 0..63
//
	private static final byte[] codes = new byte[256];
	static {
		for (int i = 0; i < 256; i++)
			codes[i] = -1;
		for (int i = 'A'; i <= 'Z'; i++)
			codes[i] = (byte) (i - 'A');
		for (int i = 'a'; i <= 'z'; i++)
			codes[i] = (byte) (26 + i - 'a');
		for (int i = '0'; i <= '9'; i++)
			codes[i] = (byte) (52 + i - '0');
		codes['+'] = 62;
		codes['/'] = 63;
	}

}