字符编码 Base64Coder

Base64Coder是一个常用的编码类，经常会用于各种网络数据传输时用来加密和解密用，用来确保数据的唯一性及用于Base64编码用在HTTP环境下传递较长的标识信息。因此这个编码是相当有用的，下面将和大家分享一下这个功能类：

核心代码：

public class Base64Coder {

// The line separator string of the operating system.
private static final String systemLineSeparator = System.getProperty("line.separator");

// Mapping table from 6-bit nibbles to Base64 characters.
private static char[] map1 = new char[64];
static {
int i = 0;
for (char c = 'A'; c <= 'Z'; c++)
map1[i++] = c;
for (char c = 'a'; c <= 'z'; c++)
map1[i++] = c;
for (char c = '0'; c <= '9'; c++)
map1[i++] = c;
map1[i++] = '+';
map1[i++] = '/';
}

// Mapping table from Base64 characters to 6-bit nibbles.
private static byte[] map2 = new byte[128];
static {
for (int i = 0; i < map2.length; i++)
map2[i] = -1;
for (int i = 0; i < 64; i++)
map2[map1[i]] = (byte) i;
}

/**
* Encodes a string into Base64 format. No blanks or line breaks are
* inserted.
*
* @param s
* A String to be encoded.
* @return A String containing the Base64 encoded data.
*/
public static String encodeString(String s) {
return new String(encode(s.getBytes()));
}

/**
* Encodes a byte array into Base 64 format and breaks the output into lines
* of 76 characters. This method is compatible with
* <code>sun.misc.BASE64Encoder.encodeBuffer(byte[])</code>.
*
* @param in
* An array containing the data bytes to be encoded.
* @return A String containing the Base64 encoded data, broken into lines.
*/
public static String encodeLines(byte[] in) {
return encodeLines(in, 0, in.length, 76, systemLineSeparator);
}

/**
* Encodes a byte array into Base 64 format and breaks the output into
* lines.
*
* @param in
* An array containing the data bytes to be encoded.
* @param iOff
* Offset of the first byte in <code>in</code> to be processed.
* @param iLen
* Number of bytes to be processed in <code>in</code>, starting
* at <code>iOff</code>.
* @param lineLen
* Line length for the output data. Should be a multiple of 4.
* @param lineSeparator
* The line separator to be used to separate the output lines.
* @return A String containing the Base64 encoded data, broken into lines.
*/
public static String encodeLines(byte[] in, int iOff, int iLen, int lineLen, String lineSeparator) {
int blockLen = (lineLen * 3) / 4;
if (blockLen <= 0)
throw new IllegalArgumentException();
int lines = (iLen + blockLen - 1) / blockLen;
int bufLen = ((iLen + 2) / 3) * 4 + lines * lineSeparator.length();
StringBuilder buf = new StringBuilder(bufLen);
int ip = 0;
while (ip < iLen) {
int l = Math.min(iLen - ip, blockLen);
buf.append(encode(in, iOff + ip, l));
buf.append(lineSeparator);
ip += l;
}
return buf.toString();
}

/**
* Encodes a byte array into Base64 format. No blanks or line breaks are
* inserted in the output.
*
* @param in
* An array containing the data bytes to be encoded.
* @return A character array containing the Base64 encoded data.
*/
public static char[] encode(byte[] in) {
return encode(in, 0, in.length);
}

/**
* Encodes a byte array into Base64 format. No blanks or line breaks are
* inserted in the output.
*
* @param in
* An array containing the data bytes to be encoded.
* @param iLen
* Number of bytes to process in <code>in</code>.
* @return A character array containing the Base64 encoded data.
*/
public static char[] encode(byte[] in, int iLen) {
return encode(in, 0, iLen);
}

/**
* Encodes a byte array into Base64 format. No blanks or line breaks are
* inserted in the output.
*
* @param in
* An array containing the data bytes to be encoded.
* @param iOff
* Offset of the first byte in <code>in</code> to be processed.
* @param iLen
* Number of bytes to process in <code>in</code>, starting at
* <code>iOff</code>.
* @return A character array containing the Base64 encoded data.
*/
public static char[] encode(byte[] in, int iOff, int iLen) {
int oDataLen = (iLen * 4 + 2) / 3; // output length without padding
int oLen = ((iLen + 2) / 3) * 4; // output length including padding
char[] out = new char[oLen];
int ip = iOff;
int iEnd = iOff + iLen;
int op = 0;
while (ip < iEnd) {
int i0 = in[ip++] & 0xff;
int i1 = ip < iEnd ? in[ip++] & 0xff : 0;
int i2 = ip < iEnd ? in[ip++] & 0xff : 0;
int o0 = i0 >>> 2;
int o1 = ((i0 & 3) << 4) | (i1 >>> 4);
int o2 = ((i1 & 0xf) << 2) | (i2 >>> 6);
int o3 = i2 & 0x3F;
out[op++] = map1[o0];
out[op++] = map1[o1];
out[op] = op < oDataLen ? map1[o2] : '=';
op++;
out[op] = op < oDataLen ? map1[o3] : '=';
op++;
}
return out;
}

/**
* Decodes a string from Base64 format. No blanks or line breaks are allowed
* within the Base64 encoded input data.
*
* @param s
* A Base64 String to be decoded.
* @return A String containing the decoded data.
* @throws IllegalArgumentException
* If the input is not valid Base64 encoded data.
*/
public static String decodeString(String s) {
return new String(decode(s));
}

/**
* Decodes a byte array from Base64 format and ignores line separators, tabs
* and blanks. CR, LF, Tab and Space characters are ignored in the input
* data. This method is compatible with
* <code>sun.misc.BASE64Decoder.decodeBuffer(String)</code>.
*
* @param s
* A Base64 String to be decoded.
* @return An array containing the decoded data bytes.
* @throws IllegalArgumentException
* If the input is not valid Base64 encoded data.
*/
public static byte[] decodeLines(String s) {
char[] buf = new char[s.length()];
int p = 0;
for (int ip = 0; ip < s.length(); ip++) {
char c = s.charAt(ip);
if (c != ' ' && c != '\r' && c != '\n' && c != '\t')
buf[p++] = c;
}
return decode(buf, 0, p);
}

/**
* Decodes a byte array from Base64 format. No blanks or line breaks are
* allowed within the Base64 encoded input data.
*
* @param s
* A Base64 String to be decoded.
* @return An array containing the decoded data bytes.
* @throws IllegalArgumentException
* If the input is not valid Base64 encoded data.
*/
public static byte[] decode(String s) {
return decode(s.toCharArray());
}

/**
* Decodes a byte array from Base64 format. No blanks or line breaks are
* allowed within the Base64 encoded input data.
*
* @param in
* A character array containing the Base64 encoded data.
* @return An array containing the decoded data bytes.
* @throws IllegalArgumentException
* If the input is not valid Base64 encoded data.
*/
public static byte[] decode(char[] in) {
return decode(in, 0, in.length);
}

/**
4000

* Decodes a byte array from Base64 format. No blanks or line breaks are
* allowed within the Base64 encoded input data.
*
* @param in
* A character array containing the Base64 encoded data.
* @param iOff
* Offset of the first character in <code>in</code> to be
* processed.
* @param iLen
* Number of characters to process in <code>in</code>, starting
* at <code>iOff</code>.
* @return An array containing the decoded data bytes.
* @throws IllegalArgumentException
* If the input is not valid Base64 encoded data.
*/
public static byte[] decode(char[] in, int iOff, int iLen) {
if (iLen % 4 != 0)
throw new IllegalArgumentException("Length of Base64 encoded input string is not a multiple of 4.");
while (iLen > 0 && in[iOff + iLen - 1] == '=')
iLen--;
int oLen = (iLen * 3) / 4;
byte[] out = new byte[oLen];
int ip = iOff;
int iEnd = iOff + iLen;
int op = 0;
while (ip < iEnd) {
int i0 = in[ip++];
int i1 = in[ip++];
int i2 = ip < iEnd ? in[ip++] : 'A';
int i3 = ip < iEnd ? in[ip++] : 'A';
if (i0 > 127 || i1 > 127 || i2 > 127 || i3 > 127)
throw new IllegalArgumentException("Illegal character in Base64 encoded data.");
int b0 = map2[i0];
int b1 = map2[i1];
int b2 = map2[i2];
int b3 = map2[i3];
if (b0 < 0 || b1 < 0 || b2 < 0 || b3 < 0)
throw new IllegalArgumentException("Illegal character in Base64 encoded data.");
int o0 = (b0 << 2) | (b1 >>> 4);
int o1 = ((b1 & 0xf) << 4) | (b2 >>> 2);
int o2 = ((b2 & 3) << 6) | b3;
out[op++] = (byte) o0;
if (op < oLen)
out[op++] = (byte) o1;
if (op < oLen)
out[op++] = (byte) o2;
}
return out;
}

// Dummy constructor.
private Base64Coder() {
}

} // end class Base64Coder

更多的移动互联网的发展趋势、app开发、移动互联网应用相关的资料请到互联网的一点事：www.yidin.net 留言

android QQ群：222392467

资料：
http://www.yidin.net/?p=8280 http://www.yidin.net/?p=9725