图片从数据流转换为字符型，方便网络传输 base64转换

android不能直接利用java里的base64类，需要自己定义编写一个编码类，从而达到可以在网络中传输照片的目的，以下就是构建一个编码类型，便于进行网络传输。

构建一个base64类：

public class base64 {

private static final byte[] encodingTable = { (byte) 'A', (byte) 'B',
(byte) 'C', (byte) 'D', (byte) 'E', (byte) 'F', (byte) 'G',
(byte) 'H', (byte) 'I', (byte) 'J', (byte) 'K', (byte) 'L',
(byte) 'M', (byte) 'N', (byte) 'O', (byte) 'P', (byte) 'Q',
(byte) 'R', (byte) 'S', (byte) 'T', (byte) 'U', (byte) 'V',
(byte) 'W', (byte) 'X', (byte) 'Y', (byte) 'Z', (byte) 'a',
(byte) 'b', (byte) 'c', (byte) 'd', (byte) 'e', (byte) 'f',
(byte) 'g', (byte) 'h', (byte) 'i', (byte) 'j', (byte) 'k',
(byte) 'l', (byte) 'm', (byte) 'n', (byte) 'o', (byte) 'p',
(byte) 'q', (byte) 'r', (byte) 's', (byte) 't', (byte) 'u',
(byte) 'v', (byte) 'w', (byte) 'x', (byte) 'y', (byte) 'z',
(byte) '0', (byte) '1', (byte) '2', (byte) '3', (byte) '4',
(byte) '5', (byte) '6', (byte) '7', (byte) '8', (byte) '9',
(byte) '+', (byte) '/' };

private static final byte[] decodingTable;

static {
decodingTable = new byte[128];
for (int i = 0; i < 128; i++) {
decodingTable[i] = (byte) -1;
}
for (int i = 'A'; i <= 'Z'; i++) {
decodingTable[i] = (byte) (i - 'A');
}
for (int i = 'a'; i <= 'z'; i++) {
decodingTable[i] = (byte) (i - 'a' + 26);
}
for (int i = '0'; i <= '9'; i++) {
decodingTable[i] = (byte) (i - '0' + 52);
}
decodingTable['+'] = 62;
decodingTable['/'] = 63;
}

public static byte[] encode(byte[] data) {
byte[] bytes;
int modulus = data.length % 3;
if (modulus == 0) {
bytes = new byte[(4 * data.length) / 3];
} else {
bytes = new byte[4 * ((data.length / 3) + 1)];
}
int dataLength = (data.length - modulus);
int a1;
int a2;
int a3;
for (int i = 0, j = 0; i < dataLength; i += 3, j += 4) {
a1 = data[i] & 0xff;
a2 = data[i + 1] & 0xff;
a3 = data[i + 2] & 0xff;
bytes[j] = encodingTable[(a1 >>> 2) & 0x3f];
bytes[j + 1] = encodingTable[((a1 << 4) | (a2 >>> 4)) & 0x3f];
bytes[j + 2] = encodingTable[((a2 << 2) | (a3 >>> 6)) & 0x3f];
bytes[j + 3] = encodingTable[a3 & 0x3f];
}
int b1;
int b2;
int b3;
int d1;
int d2;
switch (modulus) {
case 0: /* nothing left to do */
break;
case 1:
d1 = data[data.length - 1] & 0xff;
b1 = (d1 >>> 2) & 0x3f;
b2 = (d1 << 4) & 0x3f;
bytes[bytes.length - 4] = encodingTable[b1];
bytes[bytes.length - 3] = encodingTable[b2];
bytes[bytes.length - 2] = (byte) '=';
bytes[bytes.length - 1] = (byte) '=';
break;
case 2:
d1 = data[data.length - 2] & 0xff;
d2 = data[data.length - 1] & 0xff;
b1 = (d1 >>> 2) & 0x3f;
b2 = ((d1 << 4) | (d2 >>> 4)) & 0x3f;
b3 = (d2 << 2) & 0x3f;
bytes[bytes.length - 4] = encodingTable[b1];
bytes[bytes.length - 3] = encodingTable[b2];
bytes[bytes.length - 2] = encodingTable[b3];
bytes[bytes.length - 1] = (byte) '=';
break;
}
return bytes;
}

public static byte[] decode(byte[] data) {
byte[] bytes;
byte b1;
byte b2;
byte b3;
byte b4;
data = discardNonBase64Bytes(data);
if (data[data.length - 2] == '=') {
bytes = new byte[(((data.length / 4) - 1) * 3) + 1];
} else if (data[data.length - 1] == '=') {
bytes = new byte[(((data.length / 4) - 1) * 3) + 2];
} else {
bytes = new byte[((data.length / 4) * 3)];
}
for (int i = 0, j = 0; i < (data.length - 4); i += 4, j += 3) {
b1 = decodingTable[data[i]];
b2 = decodingTable[data[i + 1]];
b3 = decodingTable[data[i + 2]];
b4 = decodingTable[data[i + 3]];
bytes[j] = (byte) ((b1 << 2) | (b2 >> 4));
bytes[j + 1] = (byte) ((b2 << 4) | (b3 >> 2));
bytes[j + 2] = (byte) ((b3 << 6) | b4);
}
if (data[data.length - 2] == '=') {
b1 = decodingTable[data[data.length - 4]];
b2 = decodingTable[data[data.length - 3]];
bytes[bytes.length - 1] = (byte) ((b1 << 2) | (b2 >> 4));
} else if (data[data.length - 1] == '=') {
b1 = decodingTable[data[data.length - 4]];
b2 = decodingTable[data[data.length - 3]];
b3 = decodingTable[data[data.length - 2]];
bytes[bytes.length - 2] = (byte) ((b1 << 2) | (b2 >> 4));
bytes[bytes.length - 1] = (byte) ((b2 << 4) | (b3 >> 2));
} else {
b1 = decodingTable[data[data.length - 4]];
b2 = decodingTable[data[data.length - 3]];
b3 = decodingTable[data[data.length - 2]];
b4 = decodingTable[data[data.length - 1]];
bytes[bytes.length - 3] = (byte) ((b1 << 2) | (b2 >> 4));
bytes[bytes.length - 2] = (byte) ((b2 << 4) | (b3 >> 2));
bytes[bytes.length - 1] = (byte) ((b3 << 6) | b4);
}
return bytes;
}

public static byte[] decode(String data) {
byte[] bytes;
byte b1;
byte b2;
byte b3;
byte b4;
data = discardNonBase64Chars(data);
if (data.charAt(data.length() - 2) == '=') {
bytes = new byte[(((data.length() / 4) - 1) * 3) + 1];
} else if (data.charAt(data.length() - 1) == '=') {
bytes = new byte[(((data.length() / 4) - 1) * 3) + 2];
} else {
bytes = new byte[((data.length() / 4) * 3)];
}
for (int i = 0, j = 0; i < (data.length() - 4); i += 4, j += 3) {
b1 = decodingTable[data.charAt(i)];
b2 = decodingTable[data.charAt(i + 1)];
b3 = decodingTable[data.charAt(i + 2)];
b4 = decodingTable[data.charAt(i + 3)];
bytes[j] = (byte) ((b1 << 2) | (b2 >> 4));
bytes[j + 1] = (byte) ((b2 << 4) | (b3 >> 2));
bytes[j + 2] = (byte) ((b3 << 6) | b4);
}
if (data.charAt(data.length() - 2) == '=') {
b1 = decodingTable[data.charAt(data.length() - 4)];
b2 = decodingTable[data.charAt(data.length() - 3)];
bytes[bytes.length - 1] = (byte) ((b1 << 2) | (b2 >> 4));
} else if (data.charAt(data.length() - 1) == '=') {
b1 = decodingTable[data.charAt(data.length() - 4)];
b2 = decodingTable[data.charAt(data.length() - 3)];
b3 = decodingTable[data.charAt(data.length() - 2)];
bytes[bytes.length - 2] = (byte) ((b1 << 2) | (b2 >> 4));
bytes[bytes.length - 1] = (byte) ((b2 << 4) | (b3 >> 2));
} else {
b1 = decodingTable[data.charAt(data.length() - 4)];
b2 = decodingTable[data.charAt(data.length() - 3)];
b3 = decodingTable[data.charAt(data.length() - 2)];
b4 = decodingTable[data.charAt(data.length() - 1)];
bytes[bytes.length - 3] = (byte) ((b1 << 2) | (b2 >> 4));
bytes[bytes.length - 2] = (byte) ((b2 << 4) | (b3 >> 2));
bytes[bytes.length - 1] = (byte) ((b3 << 6) | b4);
}
return bytes;
}

private static byte[] discardNonBase64Bytes(byte[] data) {
byte[] temp = new byte[data.length];
int bytesCopied = 0;
for (int i = 0; i < data.length; i++) {
if (isValidBase64Byte(data[i])) {
temp[bytesCopied++] = data[i];
}
}
byte[] newData = new byte[bytesCopied];
System.arraycopy(temp, 0, newData, 0, bytesCopied);
return newData;
}

private static String discardNonBase64Chars(String data) {
StringBuffer sb = new StringBuffer();
int length = data.length();
for (int i = 0; i < length; i++) {
if (isValidBase64Byte((byte) (data.charAt(i)))) {
sb.append(data.charAt(i));
}
}
return sb.toString();
}

private static boolean isValidBase64Byte(byte b) {
if (b == '=') {
return true;
} else if ((b < 0) || (b >= 128)) {
return false;
} else if (decodingTable[b] == -1) {
return false;
}
return true;
}
}

转换的实例为：

public static String ReadFile(File file) {
String result = "";
FileInputStream fis = null;
byte[] xml = null;
try {
if (file != null) {
fis = new FileInputStream(file);
if (fis != null) {
int len = fis.available();
xml = new byte[len];
fis.read(xml);
}
base64 enc = new base64();
byte[] bb = enc.encode(xml);
result = new String(bb,"UTF-8");
}
} catch (IOException e) {
e.printStackTrace();
} finally {
if(fis!=null){
try {
fis.close();
fis = null;
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
return result;
}

此时的result即为转换后的字符型，解析的时候按照java的base64解析即可