AS3的BASE64编码与解码类

  调用代码：

import com.dynamicflash.utils.Base64;      
  
//编码和解码字符串     
var source:String = "Hello, world";      
var encoded:String = Base64.encode(source);      
trace(encoded);      
     
var decoded:String = Base64.decode(encoded);      
trace(decoded);     
  
//编码和解码ByteArray     
var obj:Object= {name:"Dynamic Flash",url:"http://dynamicflash.com"};   
var source:ByteArray = new ByteArray();   
source.writeObject(obj);   
  
var encoded:String = Base64.encodeByteArray(source);   
trace(encoded);   
  
var decoded:ByteArray = Base64.decodeToByteArray(encoded);   
obj = decoded.readObject();   
trace(obj.name + "(" + obj.url + ")"); 

package com.dynamicflash.util{   
  
    import flash.utils.ByteArray;   
       
    public class Base64 {   
           
        private static const BASE64_CHARS:String = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=";   
  
        public static const version:String = "1.0.0";   
  
        public static function encode(data:String):String {   
            // Convert string to ByteArray   
            var bytes:ByteArray = new ByteArray();   
            bytes.writeUTFBytes(data);   
               
            // Return encoded ByteArray   
            return encodeByteArray(bytes);   
        }   
           
        public static function encodeByteArray(data:ByteArray):String {   
            // Initialise output   
            var output:String = "";   
               
            // Create data and output buffers   
            var dataBuffer:Array;   
            var outputBuffer:Array = new Array(4);   
               
            // Rewind ByteArray   
            data.position = 0;   
               
            // while there are still bytes to be processed   
            while (data.bytesAvailable > 0) {   
                // Create new data buffer and populate next 3 bytes from data   
                dataBuffer = new Array();   
                for (var i:uint = 0; i < 3 && data.bytesAvailable > 0; i++) {   
                    dataBuffer[i] = data.readUnsignedByte();   
                }   
                   
                // Convert to data buffer Base64 character positions and    
                // store in output buffer   
                outputBuffer[0] = (dataBuffer[0] & 0xfc) >> 2;   
                outputBuffer[1] = ((dataBuffer[0] & 0x03) << 4) | ((dataBuffer[1]) >> 4);   
                outputBuffer[2] = ((dataBuffer[1] & 0x0f) << 2) | ((dataBuffer[2]) >> 6);   
                outputBuffer[3] = dataBuffer[2] & 0x3f;   
                   
                // If data buffer was short (i.e not 3 characters) then set   
                // end character indexes in data buffer to index of '=' symbol.   
                // This is necessary because Base64 data is always a multiple of   
                // 4 bytes and is basses with '=' symbols.   
                for (var j:uint = dataBuffer.length; j < 3; j++) {   
                    outputBuffer[j + 1] = 64;   
                }   
                   
                // Loop through output buffer and add Base64 characters to    
                // encoded data string for each character.   
                for (var k:uint = 0; k < outputBuffer.length; k++) {   
                    output += BASE64_CHARS.charAt(outputBuffer[k]);   
                }   
            }   
               
            // Return encoded data   
            return output;   
        }   
           
        public static function decode(data:String):String {   
            // Decode data to ByteArray   
            var bytes:ByteArray = decodeToByteArray(data);   
               
            // Convert to string and return   
            return bytes.readUTFBytes(bytes.length);   
        }   
           
        public static function decodeToByteArray(data:String):ByteArray {   
            // Initialise output ByteArray for decoded data   
            var output:ByteArray = new ByteArray();   
               
            // Create data and output buffers   
            var dataBuffer:Array = new Array(4);   
            var outputBuffer:Array = new Array(3);   
  
            // While there are data bytes left to be processed   
            for (var i:uint = 0; i < data.length; i += 4) {   
                // Populate data buffer with position of Base64 characters for   
                // next 4 bytes from encoded data   
                for (var j:uint = 0; j < 4 && i + j < data.length; j++) {   
                    dataBuffer[j] = BASE64_CHARS.indexOf(data.charAt(i + j));   
                }   
                   
                // Decode data buffer back into bytes   
                outputBuffer[0] = (dataBuffer[0] << 2) + ((dataBuffer[1] & 0x30) >> 4);   
                outputBuffer[1] = ((dataBuffer[1] & 0x0f) << 4) + ((dataBuffer[2] & 0x3c) >> 2);           
                outputBuffer[2] = ((dataBuffer[2] & 0x03) << 6) + dataBuffer[3];   
                   
                // Add all non-padded bytes in output buffer to decoded data   
                for (var k:uint = 0; k < outputBuffer.length; k++) {   
                    if (dataBuffer[k+1] == 64) break;   
                    output.writeByte(outputBuffer[k]);   
                }   
            }   
               
            // Rewind decoded data ByteArray   
            output.position = 0;   
               
            // Return decoded data   
            return output;   
        }   
           
        public function Base64() {   
            throw new Error("Base64 class is static container only");   
        }   
    }   
}