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Base64.javaAPI DocAndroid 1.5 API5353Wed May 06 22:41:56 BST 2009com.google.android.mms.pdu

Base64

public class Base64 extends Object

Fields Summary
static final int
FOURBYTE
Used to get the number of Quadruples.
static final byte
PAD
Byte used to pad output.
static final int
BASELENGTH
The base length.
private static byte[]
base64Alphabet
Constructors Summary
Methods Summary
public static byte[]decodeBase64(byte[] base64Data)
Decodes Base64 data into octects

param
base64Data Byte array containing Base64 data
return
Array containing decoded data.


    // Populating the character arrays
     
        for (int i = 0; i < BASELENGTH; i++) {
            base64Alphabet[i] = (byte) -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;
    
        // RFC 2045 requires that we discard ALL non-Base64 characters
        base64Data = discardNonBase64(base64Data);

        // handle the edge case, so we don't have to worry about it later
        if (base64Data.length == 0) {
            return new byte[0];
        }

        int numberQuadruple = base64Data.length / FOURBYTE;
        byte decodedData[] = null;
        byte b1 = 0, b2 = 0, b3 = 0, b4 = 0, marker0 = 0, marker1 = 0;

        // Throw away anything not in base64Data

        int encodedIndex = 0;
        int dataIndex = 0;
        {
            // this sizes the output array properly - rlw
            int lastData = base64Data.length;
            // ignore the '=' padding
            while (base64Data[lastData - 1] == PAD) {
                if (--lastData == 0) {
                    return new byte[0];
                }
            }
            decodedData = new byte[lastData - numberQuadruple];
        }

        for (int i = 0; i < numberQuadruple; i++) {
            dataIndex = i * 4;
            marker0 = base64Data[dataIndex + 2];
            marker1 = base64Data[dataIndex + 3];

            b1 = base64Alphabet[base64Data[dataIndex]];
            b2 = base64Alphabet[base64Data[dataIndex + 1]];

            if (marker0 != PAD && marker1 != PAD) {
                //No PAD e.g 3cQl
                b3 = base64Alphabet[marker0];
                b4 = base64Alphabet[marker1];

                decodedData[encodedIndex] = (byte) (b1 << 2 | b2 >> 4);
                decodedData[encodedIndex + 1] =
                    (byte) (((b2 & 0xf) << 4) | ((b3 >> 2) & 0xf));
                decodedData[encodedIndex + 2] = (byte) (b3 << 6 | b4);
            } else if (marker0 == PAD) {
                //Two PAD e.g. 3c[Pad][Pad]
                decodedData[encodedIndex] = (byte) (b1 << 2 | b2 >> 4);
            } else if (marker1 == PAD) {
                //One PAD e.g. 3cQ[Pad]
                b3 = base64Alphabet[marker0];

                decodedData[encodedIndex] = (byte) (b1 << 2 | b2 >> 4);
                decodedData[encodedIndex + 1] =
                    (byte) (((b2 & 0xf) << 4) | ((b3 >> 2) & 0xf));
            }
            encodedIndex += 3;
        }
        return decodedData;
static byte[]discardNonBase64(byte[] data)
Discards any characters outside of the base64 alphabet, per the requirements on page 25 of RFC 2045 - "Any characters outside of the base64 alphabet are to be ignored in base64 encoded data."

param
data The base-64 encoded data to groom
return
The data, less non-base64 characters (see RFC 2045).

        byte groomedData[] = new byte[data.length];
        int bytesCopied = 0;

        for (int i = 0; i < data.length; i++) {
            if (isBase64(data[i])) {
                groomedData[bytesCopied++] = data[i];
            }
        }

        byte packedData[] = new byte[bytesCopied];

        System.arraycopy(groomedData, 0, packedData, 0, bytesCopied);

        return packedData;
private static booleanisBase64(byte octect)
Check octect wheter it is a base64 encoding.

param
octect to be checked byte
return
ture if it is base64 encoding, false otherwise.

        if (octect == PAD) {
            return true;
        } else if (base64Alphabet[octect] == -1) {
            return false;
        } else {
            return true;
        }