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 
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* 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 
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* DEALINGS IN THE SOFTWARE. 
* 
*******************************************************************************************************************/ 

/** 
* A utility class to convert to and from base 64 encoding. 
* 
* @author <a href= "mailto:russgold@httpunit.org "> Russell Gold </a> 
**/ 
 
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])); 
 } 

}