Java tutorial
//////////////////////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/////////////////////// import java.io.*; // needed only for main() method. /** * 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. */ 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 & (int) data[i]); val <<= 8; if ((i + 1) < data.length) { val |= (0xFF & (int) data[i + 1]); trip = true; } val <<= 8; if ((i + 2) < data.length) { val |= (0xFF & (int) 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; } public static String encodeToString(byte[] data) { return new String(encode(data)); } /** * 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 (int ix = 0; ix < data.length; ix++) { if ((data[ix] > 255) || codes[data[ix]] < 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; // we now go through the entire array (NOT using the 'tempLen' value) for (int ix = 0; ix < data.length; ix++) { int value = (data[ix] > 255) ? -1 : codes[data[ix]]; 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; } public static byte[] decode(String data) { return decode(data.toCharArray()); } // // code characters for values 0..63 // static private char[] alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=" .toCharArray(); // // lookup table for converting base64 characters to value in range 0..63 // static private 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; } /////////////////////////////////////////////////// // remainder (main method and helper functions) is // for testing purposes only, feel free to clip it. /////////////////////////////////////////////////// public static void main(String[] args) { boolean decode = false; if (args.length == 0) { System.out.println("usage: java Base64 [-d[ecode]] filename"); System.exit(0); } for (int i = 0; i < args.length; i++) { if ("-decode".equalsIgnoreCase(args[i])) decode = true; else if ("-d".equalsIgnoreCase(args[i])) decode = true; } String filename = args[args.length - 1]; File file = new File(filename); if (!file.exists()) { System.out.println("Error: file '" + filename + "' doesn't exist!"); System.exit(0); } if (decode) { char[] encoded = readChars(file); byte[] decoded = decode(encoded); writeBytes(file, decoded); } else { byte[] decoded = readBytes(file); char[] encoded = encode(decoded); writeChars(file, encoded); } } private static byte[] readBytes(File file) { ByteArrayOutputStream baos = new ByteArrayOutputStream(); try { InputStream fis = new FileInputStream(file); InputStream is = new BufferedInputStream(fis); int count = 0; byte[] buf = new byte[16384]; while ((count = is.read(buf)) != -1) { if (count > 0) baos.write(buf, 0, count); } is.close(); } catch (Exception e) { e.printStackTrace(); } return baos.toByteArray(); } private static char[] readChars(File file) { CharArrayWriter caw = new CharArrayWriter(); try { Reader fr = new FileReader(file); Reader in = new BufferedReader(fr); int count = 0; char[] buf = new char[16384]; while ((count = in.read(buf)) != -1) { if (count > 0) caw.write(buf, 0, count); } in.close(); } catch (Exception e) { e.printStackTrace(); } return caw.toCharArray(); } private static void writeBytes(File file, byte[] data) { try { OutputStream fos = new FileOutputStream(file); OutputStream os = new BufferedOutputStream(fos); os.write(data); os.close(); } catch (Exception e) { e.printStackTrace(); } } private static void writeChars(File file, char[] data) { try { Writer fos = new FileWriter(file); Writer os = new BufferedWriter(fos); os.write(data); os.close(); } catch (Exception e) { e.printStackTrace(); } } /////////////////////////////////////////////////// // end of test code. /////////////////////////////////////////////////// }