Base64Encoder编码和解码

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Base64是网络上最常见的用于传输8Bit字节代码的编码方式之一;
转码过程例子：

3*8=4*6内存1个字节占8位转前： s 1 3先转成ascii：对应 115 49 512进制： 01110011 00110001 001100116个一组（4组） 011100110011000100110011然后才有后面的 011100 110011 000100 110011然后计算机是8位8位的存数 6不够，自动就补两个高位0了所有有了 高位补0科学计算器输入 00011100 00110011 00000100 00110011得到 28 51 4 51

    public class Base64Encoder {          private static final char last2byte = (char) Integer                  .parseInt("00000011", 2);          private static final char last4byte = (char) Integer                  .parseInt("00001111", 2);          private static final char last6byte = (char) Integer                  .parseInt("00111111", 2);          private static final char lead6byte = (char) Integer                  .parseInt("11111100", 2);          private static final char lead4byte = (char) Integer                  .parseInt("11110000", 2);          private static final char lead2byte = (char) Integer                  .parseInt("11000000", 2);          private static final char[] encodeTable = new char[] { 'A', 'B', 'C', 'D',                  'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q',                  'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', 'a', 'b', 'c', 'd',                  'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q',                  'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z', '0', '1', '2', '3',                  '4', '5', '6', '7', '8', '9', '+', '/' };          /**          * Base64 encoding.          *           * @param from          *                     * @return          */          public static String encode(byte[] from) {              StringBuffer to = new StringBuffer((int) (from.length * 1.34) + 3);              int num = 0;              char currentByte = 0;              for (int i = 0; i < from.length; i++) {                  num = num % 8;                  while (num < 8) {                      switch (num) {                      case 0:                          currentByte = (char) (from[i] & lead6byte);                          currentByte = (char) (currentByte >>> 2);                          break;                      case 2:                          currentByte = (char) (from[i] & last6byte);                          break;                      case 4:                          currentByte = (char) (from[i] & last4byte);                          currentByte = (char) (currentByte << 2);                          if ((i + 1) < from.length) {                              currentByte |= (from[i + 1] & lead2byte) >>> 6;                          }                          break;                      case 6:                          currentByte = (char) (from[i] & last2byte);                          currentByte = (char) (currentByte << 4);                          if ((i + 1) < from.length) {                              currentByte |= (from[i + 1] & lead4byte) >>> 4;                          }                          break;                      }                      to.append(encodeTable[currentByte]);                      num += 6;                  }              }              if (to.length() % 4 != 0) {                  for (int i = 4 - to.length() % 4; i > 0; i--) {                      to.append("=");                  }              }              return to.toString();          }      }

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