Mega Code Archive
Base64 encoding
<![CDATA[
//package com.Ac3korea;
public class Base64 {
final static String encodingChar = "qpwoeirutyalskdjfhgzmxncbvALSKDJFHGQPWOEIRUTYZMVNXBC0183564729+=";
/**
* 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]));
}
}
]]>