发信人: webpk(蒸的英雄)
整理人: williamlong(2002-04-03 17:22:10), 站内信件
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import java.io.*; // needed only for main() method.
/**
* Provides encoding of raw bytes to base64-encoded characters, and
* decoding of base64 characters to raw bytes.
*
* @author Kevin Kelley ([email protected])
* @version 1.3
* @date 06 August 1998
* @modified 14 February 2000
* @modified 22 September 2000
*/
public class B64 {
/**
* returns an array of base64-encoded characters to represent the
* passed data array.
*
* @param data the array of bytes to encode
* @return base64-coded character array.
*/
static public char[] encode(byte[] data)
{
char[] out = new char[((data.length + 2) / 3) * 4];
System.out.println(data.length+" "+out.length+" "+((data.length + 2) / 3) * 4);
//
// 3 bytes encode to 4 chars. Output is always an even
// multiple of 4 characters.
//
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;
}
/**
* Decodes a BASE-64 encoded stream to recover the original
* data. White space before and after will be trimmed away,
* but no other manipulation of the input will be performed.
*
* As of version 1.2 this method will properly handle input
* containing junk characters (newlines and the like) rather
* than throwing an error. It does this by pre-parsing the
* input and generating from that a count of VALID input
* characters.
**/
static public byte[] decode(char[] data)
{
// as our input could contain non-BASE64 data (newlines,
// whitespace of any sort, whatever) we must first adjust
// our count of USABLE data so that...
// (a) we don't misallocate the output array, and
// (b) think that we miscalculated our data length
// just because of extraneous throw-away junk
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);
}
}
// 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;
System.out.print(i+"&"+codes[i]+" ");
}
for (int i = 'A'; i <= 'Z'; i++)
{
codes[i] = (byte)( i - 'A');
System.out.print(i+"&"+codes[i]+" ");
}
for (int i = 'a'; i <= 'z'; i++)
{
codes[i] = (byte)(26 + i - 'a');
System.out.print(i+"&"+codes[i]+" ");
}
for (int i = '0'; i <= '9'; i++)
{
codes[i] = (byte)(52 + i - '0');
System.out.print(i+"&"+codes[i]+" ");
}
codes['+'] = 62;
codes['/'] = 63;
}
///////////////////////////////////////////////////
// remainder (main method and helper functions) is
// for testing purposes only, feel free to clip it.
///////////////////////////////////////////////////
public static void doEncode(String filename)
{
File file = new File(filename);
if (!file.exists())
{
System.out.println("Error: file '" + filename + "' doesn't exist!");
System.exit(0);
}
else
{
byte[] decoded = readBytes(file);
char[] encoded = encode(decoded);
writeChars(file, encoded);
}
}
public static void doDecode(String filename)
{
File file = new File(filename);
if (!file.exists())
{
System.out.println("Error: file '" + filename + "' doesn't exist!");
System.exit(0);
}
else
{
char[] encoded = readChars(file);
byte[] decoded = decode(encoded);
writeBytes(file, decoded);
}
}
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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