base64 编解码

http://www.eoeandroid.com/thread-26961-1-1.html

private static final char[] legalChars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/".toCharArray();

/** Base64 encode the given data */
public static String encode(byte[] data) {
int start = 0;
int len = data.length;
StringBuffer buf = new StringBuffer(data.length * 3 / 2);

int end = len - 3;
int i = start;
int n = 0;

while (i <= end) {
int d = ((((int) data[i]) & 0x0ff) << 16)
| ((((int) data[i + 1]) & 0x0ff) << 8)
| (((int) data[i + 2]) & 0x0ff);

buf.append(legalChars[(d >> 18) & 63]);
buf.append(legalChars[(d >> 12) & 63]);
buf.append(legalChars[(d >> 6) & 63]);
buf.append(legalChars[d & 63]);

i += 3;

if (n++ >= 14) {
n = 0;
buf.append("");
}
}

if (i == start + len - 2) {
int d = ((((int) data[i]) & 0x0ff) << 16)
| ((((int) data[i + 1]) & 255) << 8);

buf.append(legalChars[(d >> 18) & 63]);
buf.append(legalChars[(d >> 12) & 63]);
buf.append(legalChars[(d >> 6) & 63]);
buf.append("=");
} else if (i == start + len - 1) {
int d = (((int) data) & 0x0ff) << 16;

buf.append(legalChars[(d >> 18) & 63]);
buf.append(legalChars[(d >> 12) & 63]);
buf.append("==");
}

return buf.toString();
}

private static int decode(char c) {
if (c >= 'A' && c <= 'Z')
return ((int) c) - 65;
else if (c >= 'a' && c <= 'z')
return ((int) c) - 97 + 26;
else if (c >= '0' && c <= '9')
return ((int) c) - 48 + 26 + 26;
else
switch (c) {
case '+':
return 62;
case '/':
return 63;
case '=':
return 0;
default:
throw new RuntimeException("unexpected code: " + c);
}
}

/**
* Decodes the given Base64 encoded String to a new byte array. The byte
* array holding the decoded data is returned.
*/

public static byte[] decode(String s) {

ByteArrayOutputStream bos = new ByteArrayOutputStream();
try {
decode(s, bos);
} catch (IOException e) {
throw new RuntimeException();
}
byte[] decodedBytes = bos.toByteArray();
try {
bos.close();
bos = null;
} catch (IOException ex) {
System.err.println("Error while decoding BASE64: " + ex.toString());
}
return decodedBytes;
}

private static void decode(String s, OutputStream os) throws IOException {
int i = 0;

int len = s.length();

while (true) {
while (i < len && s.charAt(i) <= ' ')
i++;

if (i == len)
break;

int tri = (decode(s.charAt(i)) << 18)
+ (decode(s.charAt(i + 1)) << 12)
+ (decode(s.charAt(i + 2)) << 6)
+ (decode(s.charAt(i + 3)));

os.write((tri >> 16) & 255);
if (s.charAt(i + 2) == '=')
break;
os.write((tri >> 8) & 255);
if (s.charAt(i + 3) == '=')
break;
os.write(tri & 255);

i += 4;
}
}