sun.misc.BASE64Encoder加密类的重写

/**
 * BASE64Encoder   Class   @Override
 */
package mail;

/**
 * @author Daniel Cheng
 *
 */
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 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();

}

}