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/*
* Copyright 2005 Ralf Joachim
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
/**
* Class encodes the bytes written to the OutPutStream to a Base64 encoded string.
* The encoded string can be retrieved by as a whole by the toString() method or
* splited into lines of 72 characters by the toStringArray() method.
*
* @author <a href="mailto:ralf DOT joachim AT syscon DOT eu">Ralf Joachim</a>
* @version $Revision: 6907 $ $Date: 2005-08-05 13:58:36 -0600 (Fri, 05 Aug 2005) $
* @since 0.9.9
*/
public final class Base64Encoder {
/** Third octets in buffer. */
private static final int OCTET_3 = 3;
/** Mask buffer to or with first octet. */
private static final int OCTET_1_MASK = 0x00FFFF;
/** Mask buffer to or with second octet. */
private static final int OCTET_2_MASK = 0xFF00FF;
/** Mask buffer to or with third octet. */
private static final int OCTET_3_MASK = 0xFFFF00;
/** Mask an octet. */
private static final int OCTET_MASK = 0xFF;
/** Number of bits to shift for one octet. */
private static final int SHIFT_1_OCTET = 8;
/** Number of bits to shift for two octet. */
private static final int SHIFT_2_OCTET = 16;
/** Mask a sextet. */
private static final int SEXTET_MASK = 0x3F;
/** Number of bits to shift for one sextet. */
private static final int SHIFT_1_SEXTET = 6;
/** Number of bits to shift for two sextet. */
private static final int SHIFT_2_SEXTET = 12;
/** Number of bits to shift for three sextet. */
private static final int SHIFT_3_SEXTET = 18;
/** Array to convert sextet byte values into base64 characters. */
private static final char[] MAP = {
'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', // 00-07
'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', // 08-15
'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', // 16-23
'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f', // 24-31
'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', // 32-39
'o', 'p', 'q', 'r', 's', 't', 'u', 'v', // 40-47
'w', 'x', 'y', 'z', '0', '1', '2', '3', // 48-55
'4', '5', '6', '7', '8', '9', '+', '/', // 56-63
};
/** 24-bit buffer to translate 3 octets into 4 sextets. */
private int _buffer = 0;
/** Number of octets in buffer. */
private int _octets = 0;
/** Stream buffer for encoded characters waiting to be read. */
private StringBuffer _stream = new StringBuffer();
/**
* Encode given byte array into a encoded character array.
*
* @param bytes The byte array to be encoded.
* @return Base64 encoded characters as an array.
*/
public static char[] encode(final byte[] bytes) {
Base64Encoder enc = new Base64Encoder();
enc.translate(bytes);
return enc.getCharArray();
}
/**
* Construct a Base64Encoder.
*/
public Base64Encoder() { }
/**
* Reset Base64Encoder to its initial state. Take care using this method as it
* throws all previously written bytes away.
*/
public void reset() {
_buffer = 0;
_octets = 0;
_stream = new StringBuffer();
}
/**
* Translate all bytes of given array by appending each to octet buffer. If
* buffer contains 3 octets its content will be encoded to 4 sextet byte values
* which are converted to a base64 character each. All characters are appended
* to a StringBuffer.
*
* @param bytes The byte array to be encoded.
*/
public void translate(final byte[] bytes) {
for (int i = 0; i < bytes.length; i++) {
byte b = bytes[i];
if (_octets == 0) {
_buffer = (_buffer & OCTET_1_MASK) | ((b & OCTET_MASK) << SHIFT_2_OCTET);
} else if (_octets == 1) {
_buffer = (_buffer & OCTET_2_MASK) | ((b & OCTET_MASK) << SHIFT_1_OCTET);
} else {
_buffer = (_buffer & OCTET_3_MASK) | (b & OCTET_MASK);
}
if ((++_octets) == OCTET_3) { encode(); }
}
}
/**
* Encode 4 sextets from buffer and add them to StringBuffer.
*/
private void encode() {
_stream.append(MAP[SEXTET_MASK & (_buffer >> SHIFT_3_SEXTET)]); // sextet 1
_stream.append(MAP[SEXTET_MASK & (_buffer >> SHIFT_2_SEXTET)]); // sextet 2
_stream.append(MAP[SEXTET_MASK & (_buffer >> SHIFT_1_SEXTET)]); // sextet 3
_stream.append(MAP[SEXTET_MASK & _buffer]); // sextet 4
_buffer = 0;
_octets = 0;
}
/**
* Encode the remaining sextets from buffer and add them to to StringBuffer.
*/
private void encodeWithPadding() {
_stream.append(MAP[SEXTET_MASK & (_buffer >> SHIFT_3_SEXTET)]); // sextet 1
_stream.append(MAP[SEXTET_MASK & (_buffer >> SHIFT_2_SEXTET)]); // sextet 2
if (_octets <= 1) { // sextet 3
_stream.append('=');
} else {
_stream.append(MAP[SEXTET_MASK & (_buffer >> SHIFT_1_SEXTET)]);
}
if (_octets <= 2) { // sextet 4
_stream.append('=');
} else {
_stream.append(MAP[SEXTET_MASK & _buffer]);
}
_buffer = 0;
_octets = 0;
}
/**
* Get Base64 encoded characters as an array.
*
* @return Base64 encoded characters as an array.
*/
public char[] getCharArray() {
if (_octets > 0) { encodeWithPadding(); }
char[] chars = new char[_stream.length()];
if (_stream.length() > 0) { _stream.getChars(0, _stream.length(), chars, 0); }
return chars;
}
}
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