public static byte[] decode(byte[] base64Data) 
{
        if (base64Data == null)
            return null;
        // remove white spaces
        base64Data = removeWhiteSpace(base64Data);
        if (base64Data.length%FOURBYTE != 0) {
            return null;//should be divisible by four
        }
        int      numberQuadruple    = (base64Data.length/FOURBYTE );
        if (numberQuadruple == 0)
            return new byte[0];
        byte     decodedData[]      = null;
        byte     b1=0,b2=0,b3=0, b4=0;//, marker0=0, marker1=0;
        byte     d1=0,d2=0,d3=0,d4=0;
        // Throw away anything not in normalizedBase64Data
        // Adjust size
        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;
}

Decodes Base64 data into octects

 public static byte[] encode(byte[] binaryData) 
{
        if (binaryData == null)
            return null;
        int      lengthDataBits    = binaryData.length*EIGHTBIT;
        int      fewerThan24bits   = lengthDataBits%TWENTYFOURBITGROUP;
        int      numberTriplets    = lengthDataBits/TWENTYFOURBITGROUP;
        byte     encodedData[]     = null;
        if (fewerThan24bits != 0) //data not divisible by 24 bit
            encodedData = new byte[ (numberTriplets + 1 )*4  ];
        else // 16 or 8 bit
            encodedData = new byte[ numberTriplets*4 ];
        byte k=0, l=0, b1=0,b2=0,b3=0;
        int encodedIndex = 0;
        int dataIndex   = 0;
        int i           = 0;
        if (fDebug) {
            System.out.println("number of triplets = " + numberTriplets );
        }
        for (i = 0; i< numberTriplets; i++) {
            dataIndex = i*3;
            b1 = binaryData[dataIndex];
            b2 = binaryData[dataIndex + 1];
            b3 = binaryData[dataIndex + 2];
            if (fDebug) {
                System.out.println( "b1= " + b1 +", b2= " + b2 + ", b3= " + b3 );
            }
            l  = (byte)(b2 & 0x0f);
            k  = (byte)(b1 & 0x03);
            encodedIndex = i*4;
            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);
            encodedData[encodedIndex]   = lookUpBase64Alphabet[ val1 ];
            if (fDebug) {
                System.out.println( "val2 = " + val2 );
                System.out.println( "k4   = " + (k< < 4));
                System.out.println( "vak  = " + (val2 | (k< < 4)));
            }
            encodedData[encodedIndex+1] = lookUpBase64Alphabet[ val2 | ( k< < 4 )];
            encodedData[encodedIndex+2] = lookUpBase64Alphabet[ (l < < 2 ) | val3 ];
            encodedData[encodedIndex+3] = lookUpBase64Alphabet[ b3 & 0x3f ];
        }
        // form integral number of 6-bit groups
        dataIndex    = i*3;
        encodedIndex = i*4;
        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 + 1] = lookUpBase64Alphabet[ k< < 4 ];
            encodedData[encodedIndex + 2] = PAD;
            encodedData[encodedIndex + 3] = 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 + 1] = lookUpBase64Alphabet[ val2 | ( k< < 4 )];
            encodedData[encodedIndex + 2] = lookUpBase64Alphabet[ l< < 2 ];
            encodedData[encodedIndex + 3] = PAD;
        }
        return encodedData;
}

Encodes hex octects into Base64

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

 protected static boolean isData(byte octect) 
{
        return (base64Alphabet[octect] != -1);
}

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

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

 protected static byte[] removeWhiteSpace(byte[] data) 
{
        if (data == null)
            return null;
        // count characters that's not whitespace
        int newSize = 0;
        int len = data.length;
        for (int i = 0; i <  len; i++) {
            if (!isWhiteSpace(data[i]))
                newSize++;
        }
        // if no whitespace, just return the input array
        if (newSize == len)
            return data;
        // create the array to return
        byte[] newArray = new byte[newSize];
        int j = 0;
        for (int i = 0; i <  len; i++) {
            if (!isWhiteSpace(data[i]))
                newArray[j++] = data[i];
        }
        return newArray;
}

remove WhiteSpace from MIME containing encoded Base64 data.