Base64 工具类

public class Base64Util {

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  SIXBIT             = 6;
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] = (char)'+';
    lookUpBase64Alphabet[63] = (char)'/';

}

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

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

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

protected static boolean isBase64(char octect) {
    return (isWhiteSpace(octect) || isPad(octect) || isData(octect));
}

/**
 * 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)) {               //Two PAD e.g. 3c[Pad][Pad]
            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)) {               //One PAD  e.g. 3cQ[Pad]
            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;//an error  like "3c[Pad]r", "3cdX", "3cXd", "3cXX" where X is non data
        }
    } 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
 */
protected 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;
}

}