public final class Base64 {
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 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) '/';
}
private static boolean isWhiteSpace(char octect) {
return (octect == 0x20 || octect == 0xd || octect == 0xa || octect == 0x9);
}
private static boolean isPad(char octect) {
return (octect == PAD);
}
private static boolean isData(char octect) {
return (octect < BASELENGTH && base64Alphabet[octect] != -1);
}
/**
* 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)) {
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)) {
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;
}
} 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
*/
private 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;
}
}
来源：
http://www.icode9.com/content-4-117751.html
