src/flash/com/adobe/serialization/json/JSONEncoder.as
/*
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Copyright(c) 2005 Adobe Systems Incorporated. All rights reserved.
Please read this Source Code License Agreement carefully before using
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*/
package com.adobe.serialization.json
{
import flash.utils.describeType;
public class JSONEncoder {
/** The string that is going to represent the object we're encoding */
private var jsonString:String;
/**
* Creates a new JSONEncoder.
*
* @param o The object to encode as a JSON string
* @langversion ActionScript 3.0
* @playerversion Flash 9.0
* @tiptext
*/
public function JSONEncoder( value:* ) {
jsonString = convertToString( value );
}
/**
* Gets the JSON string from the encoder.
*
* @return The JSON string representation of the object
* that was passed to the constructor
* @langversion ActionScript 3.0
* @playerversion Flash 9.0
* @tiptext
*/
public function getString():String {
return jsonString;
}
/**
* Converts a value to it's JSON string equivalent.
*
* @param value The value to convert. Could be any
* type (object, number, array, etc)
*/
private function convertToString( value:* ):String {
// determine what value is and convert it based on it's type
if ( value is String ) {
// escape the string so it's formatted correctly
return escapeString( value as String );
} else if ( value is Number ) {
// only encode numbers that finate
return isFinite( value as Number) ? value.toString() : "null";
} else if ( value is Boolean ) {
// convert boolean to string easily
return value ? "true" : "false";
} else if ( value is Array ) {
// call the helper method to convert an array
return arrayToString( value as Array );
} else if ( value is Object && value != null ) {
// call the helper method to convert an object
return objectToString( value );
}
return "null";
}
/**
* Escapes a string accoding to the JSON specification.
*
* @param str The string to be escaped
* @return The string with escaped special characters
* according to the JSON specification
*/
private function escapeString( str:String ):String {
// create a string to store the string's jsonstring value
var s:String = "";
// current character in the string we're processing
var ch:String;
// store the length in a local variable to reduce lookups
var len:Number = str.length;
// loop over all of the characters in the string
for ( var i:int = 0; i < len; i++ ) {
// examine the character to determine if we have to escape it
ch = str.charAt( i );
switch ( ch ) {
case '"': // quotation mark
s += "\\\"";
break;
//case '/': // solidus
// s += "\\/";
// break;
case '\\': // reverse solidus
s += "\\\\";
break;
case '\b': // bell
s += "\\b";
break;
case '\f': // form feed
s += "\\f";
break;
case '\n': // newline
s += "\\n";
break;
case '\r': // carriage return
s += "\\r";
break;
case '\t': // horizontal tab
s += "\\t";
break;
default: // everything else
// check for a control character and escape as unicode
if ( ch < ' ' ) {
// get the hex digit(s) of the character (either 1 or 2 digits)
var hexCode:String = ch.charCodeAt( 0 ).toString( 16 );
// ensure that there are 4 digits by adjusting
// the # of zeros accordingly.
var zeroPad:String = hexCode.length == 2 ? "00" : "000";
// create the unicode escape sequence with 4 hex digits
s += "\\u" + zeroPad + hexCode;
} else {
// no need to do any special encoding, just pass-through
s += ch;
}
} // end switch
} // end for loop
return "\"" + s + "\"";
}
/**
* Converts an array to it's JSON string equivalent
*
* @param a The array to convert
* @return The JSON string representation of <code>a</code>
*/
private function arrayToString( a:Array ):String {
// create a string to store the array's jsonstring value
var s:String = "";
// loop over the elements in the array and add their converted
// values to the string
for ( var i:int = 0; i < a.length; i++ ) {
// when the length is 0 we're adding the first element so
// no comma is necessary
if ( s.length > 0 ) {
// we've already added an element, so add the comma separator
s += ","
}
// convert the value to a string
s += convertToString( a[i] );
}
// KNOWN ISSUE: In ActionScript, Arrays can also be associative
// objects and you can put anything in them, ie:
// myArray["foo"] = "bar";
//
// These properties aren't picked up in the for loop above because
// the properties don't correspond to indexes. However, we're
// sort of out luck because the JSON specification doesn't allow
// these types of array properties.
//
// So, if the array was also used as an associative object, there
// may be some values in the array that don't get properly encoded.
//
// A possible solution is to instead encode the Array as an Object
// but then it won't get decoded correctly (and won't be an
// Array instance)
// close the array and return it's string value
return "[" + s + "]";
}
/**
* Converts an object to it's JSON string equivalent
*
* @param o The object to convert
* @return The JSON string representation of <code>o</code>
*/
private function objectToString( o:Object ):String
{
// create a string to store the object's jsonstring value
var s:String = "";
// determine if o is a class instance or a plain object
var classInfo:XML = describeType( o );
if ( classInfo.@name.toString() == "Object" )
{
// the value of o[key] in the loop below - store this
// as a variable so we don't have to keep looking up o[key]
// when testing for valid values to convert
var value:Object;
// loop over the keys in the object and add their converted
// values to the string
for ( var key:String in o )
{
// assign value to a variable for quick lookup
value = o[key];
// don't add function's to the JSON string
if ( value is Function )
{
// skip this key and try another
continue;
}
// when the length is 0 we're adding the first item so
// no comma is necessary
if ( s.length > 0 ) {
// we've already added an item, so add the comma separator
s += ","
}
s += escapeString( key ) + ":" + convertToString( value );
}
}
else // o is a class instance
{
// Loop over all of the variables and accessors in the class and
// serialize them along with their values.
for each ( var v:XML in classInfo..*.( name() == "variable" || name() == "accessor" ) )
{
// When the length is 0 we're adding the first item so
// no comma is necessary
if ( s.length > 0 ) {
// We've already added an item, so add the comma separator
s += ","
}
s += escapeString( v.@name.toString() ) + ":"
+ convertToString( o[ v.@name ] );
}
}
return "{" + s + "}";
}
}
}