JDK8/Java8源码在线阅读
/*
* Copyright (c) 2000, 2005, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation. Oracle designates this
* particular file as subject to the "Classpath" exception as provided
* by Oracle in the LICENSE file that accompanied this code.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
* or visit www.oracle.com if you need additional information or have any
* questions.
*/
package java.util.prefs;
/**
* Static methods for translating Base64 encoded strings to byte arrays
* and vice-versa.
*
* @author Josh Bloch
* @see Preferences
* @since 1.4
*/
class Base64 {
/**
* Translates the specified byte array into a Base64 string as per
* Preferences.put(byte[]).
*/
static String byteArrayToBase64(byte[] a) {
return byteArrayToBase64(a, false);
}
/**
* Translates the specified byte array into an "alternate representation"
* Base64 string. This non-standard variant uses an alphabet that does
* not contain the uppercase alphabetic characters, which makes it
* suitable for use in situations where case-folding occurs.
*/
static String byteArrayToAltBase64(byte[] a) {
return byteArrayToBase64(a, true);
}
private static String byteArrayToBase64(byte[] a, boolean alternate) {
int aLen = a.length;
int numFullGroups = aLen/3;
int numBytesInPartialGroup = aLen - 3*numFullGroups;
int resultLen = 4*((aLen + 2)/3);
StringBuffer result = new StringBuffer(resultLen);
char[] intToAlpha = (alternate ? intToAltBase64 : intToBase64);
// Translate all full groups from byte array elements to Base64
int inCursor = 0;
for (int i=0; i<numFullGroups; i++) {
int byte0 = a[inCursor++] & 0xff;
int byte1 = a[inCursor++] & 0xff;
int byte2 = a[inCursor++] & 0xff;
result.append(intToAlpha[byte0 >> 2]);
result.append(intToAlpha[(byte0 << 4)&0x3f | (byte1 >> 4)]);
result.append(intToAlpha[(byte1 << 2)&0x3f | (byte2 >> 6)]);
result.append(intToAlpha[byte2 & 0x3f]);
}
// Translate partial group if present
if (numBytesInPartialGroup != 0) {
int byte0 = a[inCursor++] & 0xff;
result.append(intToAlpha[byte0 >> 2]);
if (numBytesInPartialGroup == 1) {
result.append(intToAlpha[(byte0 << 4) & 0x3f]);
result.append("==");
} else {
// assert numBytesInPartialGroup == 2;
int byte1 = a[inCursor++] & 0xff;
result.append(intToAlpha[(byte0 << 4)&0x3f | (byte1 >> 4)]);
result.append(intToAlpha[(byte1 << 2)&0x3f]);
result.append('=');
}
}
// assert inCursor == a.length;
// assert result.length() == resultLen;
return result.toString();
}
/**
* This array is a lookup table that translates 6-bit positive integer
* index values into their "Base64 Alphabet" equivalents as specified
* in Table 1 of RFC 2045.
*/
private static final char intToBase64[] = {
'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M',
'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z',
'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm',
'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z',
'0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '+', '/'
};
/**
* This array is a lookup table that translates 6-bit positive integer
* index values into their "Alternate Base64 Alphabet" equivalents.
* This is NOT the real Base64 Alphabet as per in Table 1 of RFC 2045.
* This alternate alphabet does not use the capital letters. It is
* designed for use in environments where "case folding" occurs.
*/
private static final char intToAltBase64[] = {
'!', '"', '#', '$', '%', '&', '\'', '(', ')', ',', '-', '.', ':',
';', '<', '>', '@', '[', ']', '^', '`', '_', '{', '|', '}', '~',
'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm',
'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z',
'0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '+', '?'
};
/**
* Translates the specified Base64 string (as per Preferences.get(byte[]))
* into a byte array.
*
* @throw IllegalArgumentException if <tt>s</tt> is not a valid Base64
* string.
*/
static byte[] base64ToByteArray(String s) {
return base64ToByteArray(s, false);
}
/**
* Translates the specified "alternate representation" Base64 string
* into a byte array.
*
* @throw IllegalArgumentException or ArrayOutOfBoundsException
* if <tt>s</tt> is not a valid alternate representation
* Base64 string.
*/
static byte[] altBase64ToByteArray(String s) {
return base64ToByteArray(s, true);
}
private static byte[] base64ToByteArray(String s, boolean alternate) {
byte[] alphaToInt = (alternate ? altBase64ToInt : base64ToInt);
int sLen = s.length();
int numGroups = sLen/4;
if (4*numGroups != sLen)
throw new IllegalArgumentException(
"String length must be a multiple of four.");
int missingBytesInLastGroup = 0;
int numFullGroups = numGroups;
if (sLen != 0) {
if (s.charAt(sLen-1) == '=') {
missingBytesInLastGroup++;
numFullGroups--;
}
if (s.charAt(sLen-2) == '=')
missingBytesInLastGroup++;
}
byte[] result = new byte[3*numGroups - missingBytesInLastGroup];
// Translate all full groups from base64 to byte array elements
int inCursor = 0, outCursor = 0;
for (int i=0; i<numFullGroups; i++) {
int ch0 = base64toInt(s.charAt(inCursor++), alphaToInt);
int ch1 = base64toInt(s.charAt(inCursor++), alphaToInt);
int ch2 = base64toInt(s.charAt(inCursor++), alphaToInt);
int ch3 = base64toInt(s.charAt(inCursor++), alphaToInt);
result[outCursor++] = (byte) ((ch0 << 2) | (ch1 >> 4));
result[outCursor++] = (byte) ((ch1 << 4) | (ch2 >> 2));
result[outCursor++] = (byte) ((ch2 << 6) | ch3);
}
// Translate partial group, if present
if (missingBytesInLastGroup != 0) {
int ch0 = base64toInt(s.charAt(inCursor++), alphaToInt);
int ch1 = base64toInt(s.charAt(inCursor++), alphaToInt);
result[outCursor++] = (byte) ((ch0 << 2) | (ch1 >> 4));
if (missingBytesInLastGroup == 1) {
int ch2 = base64toInt(s.charAt(inCursor++), alphaToInt);
result[outCursor++] = (byte) ((ch1 << 4) | (ch2 >> 2));
}
}
// assert inCursor == s.length()-missingBytesInLastGroup;
// assert outCursor == result.length;
return result;
}
/**
* Translates the specified character, which is assumed to be in the
* "Base 64 Alphabet" into its equivalent 6-bit positive integer.
*
* @throw IllegalArgumentException or ArrayOutOfBoundsException if
* c is not in the Base64 Alphabet.
*/
private static int base64toInt(char c, byte[] alphaToInt) {
int result = alphaToInt[c];
if (result < 0)
throw new IllegalArgumentException("Illegal character " + c);
return result;
}
/**
* This array is a lookup table that translates unicode characters
* drawn from the "Base64 Alphabet" (as specified in Table 1 of RFC 2045)
* into their 6-bit positive integer equivalents. Characters that
* are not in the Base64 alphabet but fall within the bounds of the
* array are translated to -1.
*/
private static final byte base64ToInt[] = {
-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
-1, -1, -1, -1, -1, -1, -1, -1, -1, 62, -1, -1, -1, 63, 52, 53, 54,
55, 56, 57, 58, 59, 60, 61, -1, -1, -1, -1, -1, -1, -1, 0, 1, 2, 3, 4,
5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23,
24, 25, -1, -1, -1, -1, -1, -1, 26, 27, 28, 29, 30, 31, 32, 33, 34,
35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51
};
/**
* This array is the analogue of base64ToInt, but for the nonstandard
* variant that avoids the use of uppercase alphabetic characters.
*/
private static final byte altBase64ToInt[] = {
-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 0, 1,
2, 3, 4, 5, 6, 7, 8, -1, 62, 9, 10, 11, -1 , 52, 53, 54, 55, 56, 57,
58, 59, 60, 61, 12, 13, 14, -1, 15, 63, 16, -1, -1, -1, -1, -1, -1,
/**代码未完, 请加载全部代码(NowJava.com).**/
关注时代Java
关注时代Java