static String base64encode(byte[] a) {

    int aLen = a.length;

    int numFullGroups = aLen/3;

    int numBytesInPartialGroup = aLen - 3*numFullGroups;

    int resultLen = 4*((aLen + 2)/3);

    StringBuffer result = new StringBuffer(resultLen);

    char[] intToAlpha = intToBase64;

    // Translate all full groups from byte array elements to Base64

    int inCursor = 0;

    for (int i=0; i<numFullGroups; i++) {

      int byte0 = a[inCursor++] & 0xff;

      int byte1 = a[inCursor++] & 0xff;

      int byte2 = a[inCursor++] & 0xff;

      result.append(intToAlpha[byte0 >> 2]);

      result.append(intToAlpha[(byte0 << 4)&0x3f | (byte1 >> 4)]);

      result.append(intToAlpha[(byte1 << 2)&0x3f | (byte2 >> 6)]);

      result.append(intToAlpha[byte2 & 0x3f]);

    }

    // Translate partial group if present

    if (numBytesInPartialGroup != 0) {

      int byte0 = a[inCursor++] & 0xff;

      result.append(intToAlpha[byte0 >> 2]);

      if (numBytesInPartialGroup == 1) {

        result.append(intToAlpha[(byte0 << 4) & 0x3f]);

        result.append("==");

      } else {

        // assert numBytesInPartialGroup == 2;

        int byte1 = a[inCursor++] & 0xff;

        result.append(intToAlpha[(byte0 << 4)&0x3f | (byte1 >> 4)]);

        result.append(intToAlpha[(byte1 << 2)&0x3f]);

        result.append('=');

      }

    }

    // assert inCursor == a.length;

    // assert result.length() == resultLen;

    return result.toString();

  }

  /**

   * This array is a lookup table that translates 6-bit positive integer

   * index values into their "Base64 Alphabet" equivalents as specified

   * in Table 1 of RFC 2045.

   */

  static final char intToBase64[] = {

    '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', '+', '/'

  };