Java常用工具类封装——Base64 编码和解码

import java.io.*;

/**
* Base64 编码和解码。
*
* @author jiangshuai
* @date 2016年10月03日
*/
public class Base64 {

public Base64() {
}

/**
* 功能：编码字符串
*
* @author jiangshuai
* @date 2016年10月03日
* @param data
*            源字符串
* @return String
*/
public static String encode(String data) {
return new String(encode(data.getBytes()));
}

/**
* 功能：解码字符串
*
* @author jiangshuai
* @date 2016年10月03日
* @param data
*            源字符串
* @return String
*/
public static String decode(String data) {
return new String(decode(data.toCharArray()));
}

/**
* 功能：编码byte[]
*
* @author jiangshuai
* @date 2016年10月03日
* @param data
*            源
* @return char[]
*/
public static char[] encode(byte[] data) {
char[] out = new char[((data.length + 2) / 3) * 4];
for (int i = 0, index = 0; i < data.length; i += 3, index += 4) {
boolean quad = false;
boolean trip = false;

int val = (0xFF & (int) data[i]);
val <<= 8;
if ((i + 1) < data.length) {
val |= (0xFF & (int) data[i + 1]);
trip = true;
}
val <<= 8;
if ((i + 2) < data.length) {
val |= (0xFF & (int) data[i + 2]);
quad = true;
}
out[index + 3] = alphabet[(quad ? (val & 0x3F) : 64)];
val >>= 6;
out[index + 2] = alphabet[(trip ? (val & 0x3F) : 64)];
val >>= 6;
out[index + 1] = alphabet[val & 0x3F];
val >>= 6;
out[index + 0] = alphabet[val & 0x3F];
}
return out;
}

/**
* 功能：解码
*
* @author jiangshuai
* @date 2016年10月03日
* @param data
*            编码后的字符数组
* @return byte[]
*/
public static byte[] decode(char[] data) {

int tempLen = data.length;
for (int ix = 0; ix < data.length; ix++) {
if ((data[ix] > 255) || codes[data[ix]] < 0) {
--tempLen; // ignore non-valid chars and padding
}
}
// calculate required length:
// -- 3 bytes for every 4 valid base64 chars
// -- plus 2 bytes if there are 3 extra base64 chars,
// or plus 1 byte if there are 2 extra.

int len = (tempLen / 4) * 3;
if ((tempLen % 4) == 3) {
len += 2;
}
if ((tempLen % 4) == 2) {
len += 1;

}
byte[] out = new byte[len];

int shift = 0; // # of excess bits stored in accum
int accum = 0; // excess bits
int index = 0;

// we now go through the entire array (NOT using the 'tempLen' value)
for (int ix = 0; ix < data.length; ix++) {
int value = (data[ix] > 255) ? -1 : codes[data[ix]];

if (value >= 0) { // skip over non-code
accum <<= 6; // bits shift up by 6 each time thru
shift += 6; // loop, with new bits being put in
accum |= value; // at the bottom.
if (shift >= 8) { // whenever there are 8 or more shifted in,
shift -= 8; // write them out (from the top, leaving any
out[index++] = // excess at the bottom for next iteration.
(byte) ((accum >> shift) & 0xff);
}
}
}

// if there is STILL something wrong we just have to throw up now!
if (index != out.length) {
throw new Error("Miscalculated data length (wrote " + index
+ " instead of " + out.length + ")");
}

return out;
}

/**
* 功能：编码文件
*
* @author jiangshuai
* @date 2016年10月03日
* @param file
*            源文件
*/
public static void encode(File file) throws IOException {
if (!file.exists()) {
System.exit(0);
}

else {
byte[] decoded = readBytes(file);
char[] encoded = encode(decoded);
writeChars(file, encoded);
}
file = null;
}

/**
* 功能：解码文件。
*
* @author jiangshuai
* @date 2016年10月03日
* @param file
*            源文件
* @throws IOException
*/
public static void decode(File file) throws IOException {
if (!file.exists()) {
System.exit(0);
} else {
char[] encoded = readChars(file);
byte[] decoded = decode(encoded);
writeBytes(file, decoded);
}
file = null;
}

//
// code characters for values 0..63
//
private static char[] alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/="
.toCharArray();

//
// lookup table for converting base64 characters to value in range 0..63
//
private static byte[] codes = new byte[256];
static {
for (int i = 0; i < 256; i++) {
codes[i] = -1;
// LoggerUtil.debug(i + "&" + codes[i] + " ");
}
for (int i = 'A'; i <= 'Z'; i++) {
codes[i] = (byte) (i - 'A');
// LoggerUtil.debug(i + "&" + codes[i] + " ");
}

for (int i = 'a'; i <= 'z'; i++) {
codes[i] = (byte) (26 + i - 'a');
// LoggerUtil.debug(i + "&" + codes[i] + " ");
}
for (int i = '0'; i <= '9'; i++) {
codes[i] = (byte) (52 + i - '0');
// LoggerUtil.debug(i + "&" + codes[i] + " ");
}
codes['+'] = 62;
codes['/'] = 63;
}

private static byte[] readBytes(File file) throws IOException {
ByteArrayOutputStream baos = new ByteArrayOutputStream();
byte[] b = null;
InputStream fis = null;
InputStream is = null;
try {
fis = new FileInputStream(file);
is = new BufferedInputStream(fis);
int count = 0;
byte[] buf = new byte[16384];
while ((count = is.read(buf)) != -1) {
if (count > 0) {
baos.write(buf, 0, count);
}
}
b = baos.toByteArray();

} finally {
try {
if (fis != null)
fis.close();
if (is != null)
is.close();
if (baos != null)
baos.close();
} catch (Exception e) {
System.out.println(e);
}
}

return b;
}

private static char[] readChars(File file) throws IOException {
CharArrayWriter caw = new CharArrayWriter();
Reader fr = null;
Reader in = null;
try {
fr = new FileReader(file);
in = new BufferedReader(fr);
int count = 0;
char[] buf = new char[16384];
while ((count = in.read(buf)) != -1) {
if (count > 0) {
caw.write(buf, 0, count);
}
}

} finally {
try {
if (caw != null)
caw.close();
if (in != null)
in.close();
if (fr != null)
fr.close();
} catch (Exception e) {
System.out.println(e);
}
}

return caw.toCharArray();
}

private static void writeBytes(File file, byte[] data) throws IOException {
OutputStream fos = null;
OutputStream os = null;
try {
fos = new FileOutputStream(file);
os = new BufferedOutputStream(fos);
os.write(data);

} finally {
try {
if (os != null)
os.close();
if (fos != null)
fos.close();
} catch (Exception e) {
System.out.println(e);
}
}
}

private static void writeChars(File file, char[] data) throws IOException {
Writer fos = null;
Writer os = null;
try {
fos = new FileWriter(file);
os = new BufferedWriter(fos);
os.write(data);

} finally {
try {
if (os != null)
os.close();
if (fos != null)
fos.close();
} catch (Exception e) {
e.printStackTrace();
}
}
}

// /////////////////////////////////////////////////
// end of test code.
// /////////////////////////////////////////////////

}