[摘要]= value; // at the bottom.if ( shift >= 8 ) // whenever there are 8 or more shifted in,shift -= ... = 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);
}
}
// we will also have skipped processing a padding null byte ('=') here;
// these are used ONLY for padding to an even length and do not legally
// occur as encoded data. for this reason we can ignore the fact that
// no index++ operation occurs in that special case: the out[] array is
// initialized to all-zero bytes to start with and that works to our
// advantage in this combination.
}
// 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;
}
//
// code characters for values 0..63
//
static private char[] alphabet =
"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/="
.toCharArray();
//
// lookup table for converting base64 characters to value in range 0..63
//
static private byte[] codes = new byte[256];
static {
for (int i=0; i<256; i++) codes[i] = -1;
for (int i = 'A'; i <= 'Z'; i++) codes[i] = (byte)( i - 'A');
for (int i = 'a'; i <= 'z'; i++) codes[i] = (byte)(26 + i - 'a');
for (int i = '0'; i <= '9'; i++) codes[i] = (byte)(52 + i - '0');
codes['+'] = 62;
codes['/'] = 63;
}
///////////////////////////////////////////////////
// remainder (main method and helper functions) is
// for testing purposes only, feel free to clip it.
///////////////////////////////////////////////////
public static void main(String[] args)
{
boolean decode = false;
if (args.length == 0) {
System.out.println("usage:java Base64 [-d[ecode]] filename");
System.exit(0);
}
for (int i=0; i<args.length; i++) {
if ("-decode".equalsIgnoreCase(args[i])) decode = true;
else if ("-d".equalsIgnoreCase(args[i])) decode = true;
}
String filename = args[args.length-1];
File file = new File(filename);
if (!file.exists()) {
System.out.println("Error:file '" + filename + "' doesn't exist!");
System.exit(0);
}
if (decode)
{
char[] encoded = readChars(file);
byte[] decoded = decode(encoded);
writeBytes(file, decoded);
}
else
{
byte[] decoded = readBytes(file);
char[] encoded = encode(decoded);
writeChars(file, encoded);
}
}
private static byte[] readBytes(File file)
{
ByteArrayOutputStream baos = new ByteArrayOutputStream();
try
{
InputStream fis = new FileInputStream(file);
InputStream 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);
}
is.close();
}
catch (Exception e) { e.printStackTrace(); }
return baos.toByteArray();
}
private static char[] readChars(File file)
{
CharArrayWriter caw = new CharArrayWriter();
try
{
Reader fr = new FileReader(file);
Reader 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);
}
in.close();
}
catch (Exception e) { e.printStackTrace(); }
return caw.toCharArray();
}
private static void writeBytes(File file, byte[] data) {
try {
OutputStream fos = new FileOutputStream(file);
OutputStream os = new BufferedOutputStream(fos);
os.write(data);
os.close();
}
catch (Exception e) { e.printStackTrace(); }
}
private static void writeChars(File file, char[] data) {
try {
Writer fos = new FileWriter(file);
Writer os = new BufferedWriter(fos);
os.write(data);
os.close();
}
catch (Exception e) { e.printStackTrace(); }
}
///////////////////////////////////////////////////
// end of test code.
///////////////////////////////////////////////////
}
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