Base64 编码

package com.wangzun.util;

public class Base64 {
 static private final int BASELENGTH = 128;
 static private final int LOOKUPLENGTH = 64;
 static private final int TWENTYFOURBITGROUP = 24;
 static private final int EIGHTBIT = 8;
 static private final int SIXTEENBIT = 16;
 static private final int FOURBYTE = 4;
 static private final int SIGN = -128;
 static private final char PAD = '=';
 static private final boolean fDebug = false;
 static final private byte[] base64Alphabet = new byte[BASELENGTH];
 static final private char[] lookUpBase64Alphabet = new char[LOOKUPLENGTH];

 static {
  for (int i = 0; i < BASELENGTH; ++i) {
   base64Alphabet[i] = -1;
  }
  for (int i = 'Z'; i >= 'A'; i--) {
   base64Alphabet[i] = (byte) (i - 'A');
  }
  for (int i = 'z'; i >= 'a'; i--) {
   base64Alphabet[i] = (byte) (i - 'a' + 26);
  }

  for (int i = '9'; i >= '0'; i--) {
   base64Alphabet[i] = (byte) (i - '0' + 52);
  }

  base64Alphabet['+'] = 62;
  base64Alphabet['/'] = 63;

  for (int i = 0; i <= 25; i++) {
   lookUpBase64Alphabet[i] = (char) ('A' + i);
  }

  for (int i = 26, j = 0; i <= 51; i++, j++) {
   lookUpBase64Alphabet[i] = (char) ('a' + j);
  }

  for (int i = 52, j = 0; i <= 61; i++, j++) {
   lookUpBase64Alphabet[i] = (char) ('0' + j);
  }
  lookUpBase64Alphabet[62] = '+';
  lookUpBase64Alphabet[63] = '/';

 }

 private static boolean isWhiteSpace(char octect) {
  return (octect == 0x20 || octect == 0xd || octect == 0xa || octect == 0x9);
 }

 private static boolean isPad(char octect) {
  return (octect == PAD);
 }

 private static boolean isData(char octect) {
  return (octect < BASELENGTH && base64Alphabet[octect] != -1);
 }

 /**
  * Encodes hex octects into Base64
  *
  * @param binaryData
  *            Array containing binaryData
  * @return Encoded Base64 array
  */
 public static String encode(byte[] binaryData) {

  if (binaryData == null) {
   return null;
  }

  int lengthDataBits = binaryData.length * EIGHTBIT;
  if (lengthDataBits == 0) {
   return "";
  }

  int fewerThan24bits = lengthDataBits % TWENTYFOURBITGROUP;
  int numberTriplets = lengthDataBits / TWENTYFOURBITGROUP;
  int numberQuartet = fewerThan24bits != 0 ? numberTriplets + 1
    : numberTriplets;
  char encodedData[] = null;

  encodedData = new char[numberQuartet * 4];

  byte k = 0, l = 0, b1 = 0, b2 = 0, b3 = 0;

  int encodedIndex = 0;
  int dataIndex = 0;
  if (fDebug) {
   System.out.println("number of triplets = " + numberTriplets);
  }

  for (int i = 0; i < numberTriplets; i++) {
   b1 = binaryData[dataIndex++];
   b2 = binaryData[dataIndex++];
   b3 = binaryData[dataIndex++];

   if (fDebug) {
    System.out.println("b1= " + b1 + ", b2= " + b2 + ", b3= " + b3);
   }

   l = (byte) (b2 & 0x0f);
   k = (byte) (b1 & 0x03);

   byte val1 = ((b1 & SIGN) == 0) ? (byte) (b1 >> 2)
     : (byte) ((b1) >> 2 ^ 0xc0);
   byte val2 = ((b2 & SIGN) == 0) ? (byte) (b2 >> 4)
     : (byte) ((b2) >> 4 ^ 0xf0);
   byte val3 = ((b3 & SIGN) == 0) ? (byte) (b3 >> 6)
     : (byte) ((b3) >> 6 ^ 0xfc);

   if (fDebug) {
    System.out.println("val2 = " + val2);
    System.out.println("k4   = " + (k << 4));
    System.out.println("vak  = " + (val2 | (k << 4)));
   }

   encodedData[encodedIndex++] = lookUpBase64Alphabet[val1];
   encodedData[encodedIndex++] = lookUpBase64Alphabet[val2 | (k << 4)];
   encodedData[encodedIndex++] = lookUpBase64Alphabet[(l << 2) | val3];
   encodedData[encodedIndex++] = lookUpBase64Alphabet[b3 & 0x3f];
  }

  // form integral number of 6-bit groups
  if (fewerThan24bits == EIGHTBIT) {
   b1 = binaryData[dataIndex];
   k = (byte) (b1 & 0x03);
   if (fDebug) {
    System.out.println("b1=" + b1);
    System.out.println("b1<<2 = " + (b1 >> 2));
   }
   byte val1 = ((b1 & SIGN) == 0) ? (byte) (b1 >> 2)
     : (byte) ((b1) >> 2 ^ 0xc0);
   encodedData[encodedIndex++] = lookUpBase64Alphabet[val1];
   encodedData[encodedIndex++] = lookUpBase64Alphabet[k << 4];
   encodedData[encodedIndex++] = PAD;
   encodedData[encodedIndex++] = PAD;
  } else if (fewerThan24bits == SIXTEENBIT) {
   b1 = binaryData[dataIndex];
   b2 = binaryData[dataIndex + 1];
   l = (byte) (b2 & 0x0f);
   k = (byte) (b1 & 0x03);

   byte val1 = ((b1 & SIGN) == 0) ? (byte) (b1 >> 2)
     : (byte) ((b1) >> 2 ^ 0xc0);
   byte val2 = ((b2 & SIGN) == 0) ? (byte) (b2 >> 4)
     : (byte) ((b2) >> 4 ^ 0xf0);

   encodedData[encodedIndex++] = lookUpBase64Alphabet[val1];
   encodedData[encodedIndex++] = lookUpBase64Alphabet[val2 | (k << 4)];
   encodedData[encodedIndex++] = lookUpBase64Alphabet[l << 2];
   encodedData[encodedIndex++] = PAD;
  }

  return new String(encodedData);
 }

 /**
  * Decodes Base64 data into octects
  *
  * @param encoded
  *            string containing Base64 data
  * @return Array containind decoded data.
  */
 public static byte[] decode(String encoded) {

  if (encoded == null) {
   return null;
  }

  char[] base64Data = encoded.toCharArray();
  // remove white spaces
  int len = removeWhiteSpace(base64Data);

  if (len % FOURBYTE != 0) {
   return null;// should be divisible by four
  }

  int numberQuadruple = (len / FOURBYTE);

  if (numberQuadruple == 0) {
   return new byte[0];
  }

  byte decodedData[] = null;
  byte b1 = 0, b2 = 0, b3 = 0, b4 = 0;
  char d1 = 0, d2 = 0, d3 = 0, d4 = 0;

  int i = 0;
  int encodedIndex = 0;
  int dataIndex = 0;
  decodedData = new byte[(numberQuadruple) * 3];

  for (; i < numberQuadruple - 1; i++) {

   if (!isData((d1 = base64Data[dataIndex++]))
     || !isData((d2 = base64Data[dataIndex++]))
     || !isData((d3 = base64Data[dataIndex++]))
     || !isData((d4 = base64Data[dataIndex++]))) {
    return null;
   }// if found "no data" just return null

   b1 = base64Alphabet[d1];
   b2 = base64Alphabet[d2];
   b3 = base64Alphabet[d3];
   b4 = base64Alphabet[d4];

   decodedData[encodedIndex++] = (byte) (b1 << 2 | b2 >> 4);
   decodedData[encodedIndex++] = (byte) (((b2 & 0xf) << 4) | ((b3 >> 2) & 0xf));
   decodedData[encodedIndex++] = (byte) (b3 << 6 | b4);
  }

  if (!isData((d1 = base64Data[dataIndex++]))
    || !isData((d2 = base64Data[dataIndex++]))) {
   return null;// if found "no data" just return null
  }

  b1 = base64Alphabet[d1];
  b2 = base64Alphabet[d2];

  d3 = base64Data[dataIndex++];
  d4 = base64Data[dataIndex++];
  if (!isData((d3)) || !isData((d4))) {// Check if they are PAD characters
   if (isPad(d3) && isPad(d4)) {
    if ((b2 & 0xf) != 0)// last 4 bits should be zero
    {
     return null;
    }
    byte[] tmp = new byte[i * 3 + 1];
    System.arraycopy(decodedData, 0, tmp, 0, i * 3);
    tmp[encodedIndex] = (byte) (b1 << 2 | b2 >> 4);
    return tmp;
   } else if (!isPad(d3) && isPad(d4)) {
    b3 = base64Alphabet[d3];
    if ((b3 & 0x3) != 0)// last 2 bits should be zero
    {
     return null;
    }
    byte[] tmp = new byte[i * 3 + 2];
    System.arraycopy(decodedData, 0, tmp, 0, i * 3);
    tmp[encodedIndex++] = (byte) (b1 << 2 | b2 >> 4);
    tmp[encodedIndex] = (byte) (((b2 & 0xf) << 4) | ((b3 >> 2) & 0xf));
    return tmp;
   } else {
    return null;
   }
  } else { // No PAD e.g 3cQl
   b3 = base64Alphabet[d3];
   b4 = base64Alphabet[d4];
   decodedData[encodedIndex++] = (byte) (b1 << 2 | b2 >> 4);
   decodedData[encodedIndex++] = (byte) (((b2 & 0xf) << 4) | ((b3 >> 2) & 0xf));
   decodedData[encodedIndex++] = (byte) (b3 << 6 | b4);

  }

  return decodedData;
 }

 /**
  * remove WhiteSpace from MIME containing encoded Base64 data.
  *
  * @param data
  *            the byte array of base64 data (with WS)
  * @return the new length
  */
 private static int removeWhiteSpace(char[] data) {
  if (data == null) {
   return 0;
  }

  // count characters that's not whitespace
  int newSize = 0;
  int len = data.length;
  for (int i = 0; i < len; i++) {
   if (!isWhiteSpace(data[i])) {
    data[newSize++] = data[i];
   }
  }
  return newSize;
 }
}