Mega Code Archive
Encodes binary data to plain text as Base64
<![CDATA[
//package com.thoughtworks.xstream.core.util;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.Reader;
import java.io.StringReader;
/**
* Encodes binary data to plain text as Base64.
*
* <p>Despite there being a gazillion other Base64 implementations out there, this has been written as part of XStream as
* it forms a core part but is too trivial to warrant an extra dependency.</p>
*
* <p>This meets the standard as described in RFC 1521, section 5.2 <http://www.freesoft.org/CIE/RFC/1521/7.htm>, allowing
* other Base64 tools to manipulate the data.</p>
*
* @author Joe Walnes
*/
public class Base64Encoder {
// Here's how encoding works:
//
// 1) Incoming bytes are broken up into groups of 3 (each byte having 8 bits).
//
// 2) The combined 24 bits (3 * 8) are split into 4 groups of 6 bits.
//
// input |------||------||------| (3 values each with 8 bits)
// 101010101010101010101010
// output |----||----||----||----| (4 values each with 6 bits)
//
// 3) Each of these 4 groups of 6 bits are converted back to a number, which will fall in the range of 0 - 63.
//
// 4) Each of these 4 numbers are converted to an alphanumeric char in a specified mapping table, to create
// a 4 character string.
//
// 5) This is repeated for all groups of three bytes.
//
// 6) Special padding is done at the end of the stream using the '=' char.
private static final char[] SIXTY_FOUR_CHARS = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/".toCharArray();
private static final int[] REVERSE_MAPPING = new int[123];
static {
for (int i = 0; i < SIXTY_FOUR_CHARS.length; i++) REVERSE_MAPPING[SIXTY_FOUR_CHARS[i]] = i + 1;
}
public String encode(byte[] input) {
StringBuffer result = new StringBuffer();
int outputCharCount = 0;
for (int i = 0; i < input.length; i += 3) {
int remaining = Math.min(3, input.length - i);
int oneBigNumber = (input[i] & 0xff) << 16 | (remaining <= 1 ? 0 : input[i + 1] & 0xff) << 8 | (remaining <= 2 ? 0 : input[i + 2] & 0xff);
for (int j = 0; j < 4; j++) result.append(remaining + 1 > j ? SIXTY_FOUR_CHARS[0x3f & oneBigNumber >> 6 * (3 - j)] : '=');
if ((outputCharCount += 4) % 76 == 0) result.append('\n');
}
return result.toString();
}
public byte[] decode(String input) {
try {
ByteArrayOutputStream out = new ByteArrayOutputStream();
StringReader in = new StringReader(input);
for (int i = 0; i < input.length(); i += 4) {
int a[] = {mapCharToInt(in), mapCharToInt(in), mapCharToInt(in), mapCharToInt(in)};
int oneBigNumber = (a[0] & 0x3f) << 18 | (a[1] & 0x3f) << 12 | (a[2] & 0x3f) << 6 | (a[3] & 0x3f);
for (int j = 0; j < 3; j++) if (a[j + 1] >= 0) out.write(0xff & oneBigNumber >> 8 * (2 - j));
}
return out.toByteArray();
} catch (IOException e) {
throw new Error(e + ": " + e.getMessage());
}
}
private int mapCharToInt(Reader input) throws IOException {
int c;
while ((c = input.read()) != -1) {
int result = REVERSE_MAPPING[c];
if (result != 0) return result -1;
if (c == '=') return -1;
}
return -1;
}
}
]]>