base64_encode和base64_decode的JAVA实现

base64_encode和base64_decode的JAVA实现

/******************************************************************************************************************** * $Id: Base64.java,v 1.4 2002/12/24 15:17:17 russgold Exp $ * * Copyright (c) 2000-2002 by Russell Gold * * Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated * documentation files (the "Software "), to deal in the Software without restriction, including without limitation * the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and * to permit persons to whom the Software is furnished to do so, subject to the following conditions: * * The above copyright notice and this permission notice shall be included in all copies or substantial portions * of the Software. * * THE SOFTWARE IS PROVIDED "AS IS ", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO * THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF * CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER * DEALINGS IN THE SOFTWARE. * *******************************************************************************************************************/ /** * A utility class to convert to and from base 64 encoding. * * @author Russell Gold **/

public class Base64 {

final static String encodingChar = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/ "; /**

* Returns the base 64 encoded equivalent of a supplied string.

* @param source the string to encode

*/

public static String encode( String source ) {

char[] sourceBytes = getPaddedBytes( source );

int numGroups = (sourceBytes.length + 2) / 3;

char[] targetBytes = new char[4];

char[] target = new char[ 4 * numGroups ];

for (int group = 0; group < numGroups; group++) {

convert3To4( sourceBytes, group*3, targetBytes );

for (int i = 0; i < targetBytes.length; i++) {

target[ i + 4*group ] = encodingChar.charAt( targetBytes[i] );

}

}

int numPadBytes = sourceBytes.length - source.length();

for (int i = target.length-numPadBytes; i < target.length; i++) target[i] = '= ';

return new String( target );

}

private static char[] getPaddedBytes( String source ) {

char[] converted = source.toCharArray();

int requiredLength = 3 * ((converted.length+2) /3);

char[] result = new char[ requiredLength ];

System.arraycopy( converted, 0, result, 0, converted.length );

return result;

}

private static void convert3To4( char[] source, int sourceIndex, char[] target ) {

target[0] = (char) ( source[ sourceIndex ] > > > 2);

target[1] = (char) (((source[ sourceIndex ] & 0x03) < < 4) | (source[ sourceIndex+1 ] > > > 4));

target[2] = (char) (((source[ sourceIndex+1 ] & 0x0f) < < 2) | (source[ sourceIndex+2 ] > > > 6));

target[3] = (char) ( source[ sourceIndex+2 ] & 0x3f);

}

/**

* Returns the plaintext equivalent of a base 64-encoded string.

* @param source a base 64 string (which must have a multiple of 4 characters)

*/

public static String decode( String source ) {

if (source.length()%4 != 0) throw new RuntimeException( "valid Base64 codes have a multiple of 4 characters " );

int numGroups = source.length() / 4;

int numExtraBytes = source.endsWith( "== " ) ? 2 : (source.endsWith( "= " ) ? 1 : 0);

byte[] targetBytes = new byte[ 3*numGroups ];

byte[] sourceBytes = new byte[4];

for (int group = 0; group < numGroups; group++) {

for (int i = 0; i < sourceBytes.length; i++) {

sourceBytes[i] = (byte) Math.max( 0, encodingChar.indexOf( source.charAt( 4*group+i ) ) );

}

convert4To3( sourceBytes, targetBytes, group*3 );

}

return new String( targetBytes, 0, targetBytes.length - numExtraBytes );

}

private static void convert4To3( byte[] source, byte[] target, int targetIndex ) {

target[ targetIndex ] = (byte) (( source[0] < < 2) | (source[1] > > > 4));

target[ targetIndex+1 ] = (byte) (((source[1] & 0x0f) < < 4) | (source[2] > > > 2));

target[ targetIndex+2 ] = (byte) (((source[2] & 0x03) < < 6) | (source[3]));

}

}

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