Base64编解码
来自Stendhal-v1.28.1中的Base64编解码实现：
//////////////////////license & copyright header/////////////////////////
// //
// Base64 - encode/decode data using the Base64 encoding scheme //
// //
// Copyright (c) 1998 by Kevin Kelley //
// //
// This library is free software; you can redistribute it and/or //
// modify it under the terms of the GNU Lesser General Public //
// License as published by the Free Software Foundation; either //
// version 2.1 of the License, or (at your option) any later version. //
// //
// This library 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 Lesser General Public License for more details. //
// //
// You should have received a copy of the GNU Lesser General Public //
// License along with this library; if not, write to the Free Software //
// Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA //
// 02111-1307, USA, or contact the author: //
// //
// Kevin Kelley <kelley@ruralnet.net> - 30718 Rd. 28, La Junta, CO, //
// 81050 USA. //
// //
////////////////////end license & copyright header///////////////////////
//Added 10May04 by Adam Turk for distribution as part
package games.stendhal.common;
//of the Tiled codebase
/**
* 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
*/
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.
*/
public static char[] encode(final byte[] data) {
final 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] = 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.
* @param data data to decode
* @return the decoded data
*/
public static byte[] decode(final 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 (int ix = 0; ix < data.length; ix++) {
if ((data[ix] > 255) || (codes[data[ix]] < 0)) {
// ignore non-valid chars and padding
--tempLen;
}
}
// 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;
}
final byte[] out = new byte[len];
// # of excess bits stored in accum
int shift = 0;
// excess bits
int accum = 0;
int index = 0;
// we now go through the entire array (NOT using the 'tempLen' value)
for (int ix = 0; ix < data.length; ix++) {
final int value = (data[ix] > 255) ? -1 : codes[data[ix]];
if (value >= 0) {
// skip over non-code
// bits shift up by 6 each time thru
accum <<= 6;
// loop, with new bits being put in
shift += 6;
// at the bottom.
accum |= value;
if (shift >= 8) {
// whenever there are 8 or more shifted in,
// write them out (from the top, leaving any
// excess at the bottom for next iteration.
shift -= 8;
out[index++] = (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 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;
}
}