这个BASE64Encoder的加密方法的解密方法怎么写？

Question

public class BASE64Encoder {
private static char[] codec_table = { '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', '+', '/' };

public BASE64Encoder() {

}

public static String encode(byte[] a) {
int totalBits = a.length * 8;
int nn = totalBits % 6;
int curPos = 0;// process bits
StringBuffer toReturn = new StringBuffer();
while (curPos < totalBits) {
int bytePos = curPos / 8;
switch (curPos % 8) {
case 0:
toReturn.append(codec_table[(a[bytePos] & 0xfc) >> 2]);
break;
case 2:

        toReturn.append(codec_table[(a[bytePos] & 0x3f)]);
        break;
    case 4:
        if (bytePos == a.length - 1) {
            toReturn.append(codec_table[((a[bytePos] & 0x0f) << 2) & 0x3f]);
        } else {
            int pos = (((a[bytePos] & 0x0f) << 2) | ((a[bytePos + 1] & 0xc0) >> 6)) & 0x3f;
            toReturn.append(codec_table[pos]);
        }

        break;
    case 6:
        if (bytePos == a.length - 1) {
            toReturn.append(codec_table[((a[bytePos] & 0x03) << 4) & 0x3f]);
        } else {
            int pos = (((a[bytePos] & 0x03) << 4) | ((a[bytePos + 1] & 0xf0) >> 4)) & 0x3f;
            toReturn.append(codec_table[pos]);
        }
        break;
    default:
        // never hanppen
        break;
    }
    curPos += 6;
}
if (nn == 2) {
    toReturn.append("==");
} else if (nn == 4) {
    toReturn.append("=");
}
return toReturn.toString();

}
}

Answer 1

Base64的编码和解码方法一般是统一的，只要了解截取原理，逆向返回去就可以了