Description
Decodes Base64 content in byte array format and returns the decoded byte array.
License
Apache License
Parameter
| Parameter | Description |
|---|
| source | The Base64 encoded data |
| off | The offset of where to begin decoding |
| len | The length of characters to decode |
Exception
| Parameter | Description |
|---|
| Base64DecoderException | an exception |
Return
decoded data
Declaration
public static byte[] decode(byte[] source, int off, int len)
throws Base64DecoderException
Method Source Code
// Licensed under the Apache License, Version 2.0 (the "License");
public class Main{
/** The equals sign (=) as a byte. */
private final static byte EQUALS_SIGN = (byte) '=';
/** The new line character (\n) as a byte. */
private final static byte NEW_LINE = (byte) '\n';
/**/*from w w w . ja v a 2s . c o m*/
* Translates a Base64 value to either its 6-bit reconstruction value
* or a negative number indicating some other meaning.
**/
private final static byte[] DECODABET = { -9, -9, -9, -9, -9, -9, -9,
-9, -9, // Decimal 0 - 8
-5, -5, // Whitespace: Tab and Linefeed
-9, -9, // Decimal 11 - 12
-5, // Whitespace: Carriage Return
-9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, // Decimal 14 - 26
-9, -9, -9, -9, -9, // Decimal 27 - 31
-5, // Whitespace: Space
-9, -9, -9, -9, -9, -9, -9, -9, -9, -9, // Decimal 33 - 42
62, // Plus sign at decimal 43
-9, -9, -9, // Decimal 44 - 46
63, // Slash at decimal 47
52, 53, 54, 55, 56, 57, 58, 59, 60, 61, // Numbers zero through nine
-9, -9, -9, // Decimal 58 - 60
-1, // Equals sign at decimal 61
-9, -9, -9, // Decimal 62 - 64
0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, // Letters 'A' through 'N'
14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, // Letters 'O' through 'Z'
-9, -9, -9, -9, -9, -9, // Decimal 91 - 96
26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, // Letters 'a' through 'm'
39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, // Letters 'n' through 'z'
-9, -9, -9, -9, -9 // Decimal 123 - 127
/* ,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9, // Decimal 128 - 139
-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9, // Decimal 140 - 152
-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9, // Decimal 153 - 165
-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9, // Decimal 166 - 178
-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9, // Decimal 179 - 191
-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9, // Decimal 192 - 204
-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9, // Decimal 205 - 217
-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9, // Decimal 218 - 230
-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9, // Decimal 231 - 243
-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9,-9 // Decimal 244 - 255 */
};
private final static byte WHITE_SPACE_ENC = -5;
private final static byte EQUALS_SIGN_ENC = -1;
/**
* Decodes data from Base64 notation.
*
* @param s the string to decode (decoded in default encoding)
* @return the decoded data
* @since 1.4
*/
public static byte[] decode(String s) throws Base64DecoderException {
byte[] bytes = s.getBytes();
return decode(bytes, 0, bytes.length);
}
/**
* Decodes Base64 content in byte array format and returns
* the decoded byte array.
*
* @param source The Base64 encoded data
* @return decoded data
* @since 1.3
* @throws Base64DecoderException
*/
public static byte[] decode(byte[] source)
throws Base64DecoderException {
return decode(source, 0, source.length);
}
/**
* Decodes Base64 content in byte array format and returns
* the decoded byte array.
*
* @param source The Base64 encoded data
* @param off The offset of where to begin decoding
* @param len The length of characters to decode
* @return decoded data
* @since 1.3
* @throws Base64DecoderException
*/
public static byte[] decode(byte[] source, int off, int len)
throws Base64DecoderException {
return decode(source, off, len, DECODABET);
}
/**
* Decodes Base64 content using the supplied decodabet and returns
* the decoded byte array.
*
* @param source The Base64 encoded data
* @param off The offset of where to begin decoding
* @param len The length of characters to decode
* @param decodabet the decodabet for decoding Base64 content
* @return decoded data
*/
public static byte[] decode(byte[] source, int off, int len,
byte[] decodabet) throws Base64DecoderException {
int len34 = len * 3 / 4;
byte[] outBuff = new byte[2 + len34]; // Upper limit on size of output
int outBuffPosn = 0;
byte[] b4 = new byte[4];
int b4Posn = 0;
int i = 0;
byte sbiCrop = 0;
byte sbiDecode = 0;
for (i = 0; i < len; i++) {
sbiCrop = (byte) (source[i + off] & 0x7f); // Only the low seven bits
sbiDecode = decodabet[sbiCrop];
if (sbiDecode >= WHITE_SPACE_ENC) { // White space Equals sign or better
if (sbiDecode >= EQUALS_SIGN_ENC) {
// An equals sign (for padding) must not occur at position 0 or 1
// and must be the last byte[s] in the encoded value
if (sbiCrop == EQUALS_SIGN) {
int bytesLeft = len - i;
byte lastByte = (byte) (source[len - 1 + off] & 0x7f);
if (b4Posn == 0 || b4Posn == 1) {
throw new Base64DecoderException(
"invalid padding byte '=' at byte offset "
+ i);
} else if ((b4Posn == 3 && bytesLeft > 2)
|| (b4Posn == 4 && bytesLeft > 1)) {
throw new Base64DecoderException(
"padding byte '=' falsely signals end of encoded value "
+ "at offset " + i);
} else if (lastByte != EQUALS_SIGN
&& lastByte != NEW_LINE) {
throw new Base64DecoderException(
"encoded value has invalid trailing byte");
}
break;
}
b4[b4Posn++] = sbiCrop;
if (b4Posn == 4) {
outBuffPosn += decode4to3(b4, 0, outBuff,
outBuffPosn, decodabet);
b4Posn = 0;
}
}
} else {
throw new Base64DecoderException(
"Bad Base64 input character at " + i + ": "
+ source[i + off] + "(decimal)");
}
}
// Because web safe encoding allows non padding base64 encodes, we
// need to pad the rest of the b4 buffer with equal signs when
// b4Posn != 0. There can be at most 2 equal signs at the end of
// four characters, so the b4 buffer must have two or three
// characters. This also catches the case where the input is
// padded with EQUALS_SIGN
if (b4Posn != 0) {
if (b4Posn == 1) {
throw new Base64DecoderException(
"single trailing character at offset " + (len - 1));
}
b4[b4Posn++] = EQUALS_SIGN;
outBuffPosn += decode4to3(b4, 0, outBuff, outBuffPosn,
decodabet);
}
byte[] out = new byte[outBuffPosn];
System.arraycopy(outBuff, 0, out, 0, outBuffPosn);
return out;
}
/**
* Decodes four bytes from array <var>source</var>
* and writes the resulting bytes (up to three of them)
* to <var>destination</var>.
* The source and destination arrays can be manipulated
* anywhere along their length by specifying
* <var>srcOffset</var> and <var>destOffset</var>.
* This method does not check to make sure your arrays
* are large enough to accommodate <var>srcOffset</var> + 4 for
* the <var>source</var> array or <var>destOffset</var> + 3 for
* the <var>destination</var> array.
* This method returns the actual number of bytes that
* were converted from the Base64 encoding.
*
*
* @param source the array to convert
* @param srcOffset the index where conversion begins
* @param destination the array to hold the conversion
* @param destOffset the index where output will be put
* @param decodabet the decodabet for decoding Base64 content
* @return the number of decoded bytes converted
* @since 1.3
*/
private static int decode4to3(byte[] source, int srcOffset,
byte[] destination, int destOffset, byte[] decodabet) {
// Example: Dk==
if (source[srcOffset + 2] == EQUALS_SIGN) {
int outBuff = ((decodabet[source[srcOffset]] << 24) >>> 6)
| ((decodabet[source[srcOffset + 1]] << 24) >>> 12);
destination[destOffset] = (byte) (outBuff >>> 16);
return 1;
} else if (source[srcOffset + 3] == EQUALS_SIGN) {
// Example: DkL=
int outBuff = ((decodabet[source[srcOffset]] << 24) >>> 6)
| ((decodabet[source[srcOffset + 1]] << 24) >>> 12)
| ((decodabet[source[srcOffset + 2]] << 24) >>> 18);
destination[destOffset] = (byte) (outBuff >>> 16);
destination[destOffset + 1] = (byte) (outBuff >>> 8);
return 2;
} else {
// Example: DkLE
int outBuff = ((decodabet[source[srcOffset]] << 24) >>> 6)
| ((decodabet[source[srcOffset + 1]] << 24) >>> 12)
| ((decodabet[source[srcOffset + 2]] << 24) >>> 18)
| ((decodabet[source[srcOffset + 3]] << 24) >>> 24);
destination[destOffset] = (byte) (outBuff >> 16);
destination[destOffset + 1] = (byte) (outBuff >> 8);
destination[destOffset + 2] = (byte) (outBuff);
return 3;
}
}
}
Related
- decode(byte[] input, int flags)
- decode(byte[] input, int offset, int len, int flags)
- decode(byte[] source)
- decode(byte[] source)
- decode(byte[] source)
- decode(byte[] source, int off, int len)
- decode(byte[] source, int off, int len)
- decode(byte[] source, int off, int len, byte[] decodabet)
- decode(byte[] source, int off, int len, byte[] decodabet)