下列範例說明復原從 JSON 字串剖析之物件的策略。這個範例會定義兩個類別：JSONGenericDictExample 和 JSONDictionaryExtnExample。類別 JSONGenericDictExample 是自訂 dictionary 類別。每個記錄會包含每人的名字和生日，以及唯一的 ID。每次呼叫 JSONGenericDictExample 建構函式時，都會將新建的物件以及靜態遞增整數 (例如它的 ID) 加入內部靜態陣列中。此外，類別 JSONGenericDictExample 還會定義
revive()
方法，以便從較長的
id
成員中只擷取整數部分。
revive()
方法會使用這個整數來尋找並傳回正確的可復原物件。
類別 JSONDictionaryExtnExample 會擴充 ActionScript Dictionary 類別。它的記錄沒有集合結構，因此可以包含任何資料。資料是在建構 JSONDictionaryExtnExample 物件之後指定的，而不是指定做為類別定義的屬性。JSONDictionaryExtnExample 記錄會將 JSONGenericDictExample 物件當做索引鍵使用。當復原 JSONDictionaryExtnExample 物件時，
JSONGenericDictExample.revive()
函數會使用與 JSONDictionaryExtnExample 關聯的 ID 來擷取正確的索引鍵物件。
最重要的是，除了 JSONDictionaryExtnExample 物件，
JSONDictionaryExtnExample.toJSON()
方法還會傳回標記字串。這個字串會將 JSON 輸出識別為屬於 JSONDictionaryExtnExample 類別。這個標記毫無疑問地成為
JSON.parse()
期間處理的物件類型。
package {
// Generic dictionary example:
public class JSONGenericDictExample {
static var revivableObjects = [];
static var nextId = 10000;
public var id;
public var dname:String;
public var birthday;
public function JSONGenericDictExample(name, birthday) {
revivableObjects[nextId] = this;
this.id = "id_class_JSONGenericDictExample_" + nextId;
this.dname = name;
this.birthday = birthday;
nextId++;
}
public function toString():String { return this.dname; }
public static function revive(id:String):JSONGenericDictExample {
var r:RegExp = /^id_class_JSONGenericDictExample_([0-9]*)$/;
var res = r.exec(id);
return JSONGenericDictExample.revivableObjects[res[1]];
}
}
}
package {
import flash.utils.Dictionary;
import flash.utils.ByteArray;
// For this extension of dictionary, we serialize the contents of the
// dictionary by using toJSON
public final class JSONDictionaryExtnExample extends Dictionary {
public function toJSON(k):* {
var contents = {};
for (var a in this) {
contents[a.id] = this[a];
}
// We also wrap the contents in an object so that we can
// identify it by looking for the marking property "class E"
// while in the midst of JSON.parse.
return {"class JSONDictionaryExtnExample": contents};
}
// This is just here for debugging and for illustration
public function toString():String {
var retval = "[JSONDictionaryExtnExample <";
var printed_any = false;
for (var k in this) {
retval += k.toString() + "=" +
"[e="+this[k].earnings +
",v="+this[k].violations + "], "
printed_any = true;
}
if (printed_any)
retval = retval.substring(0, retval.length-2);
retval += ">]"
return retval;
}
}
}
當下列執行階段指令碼呼叫 JSONDictionaryExtnExample 物件上的
JSON.parse()
時，
reviver
函數會呼叫 JSONDictionaryExtnExample 中每個物件上的
JSONGenericDictExample.revive()
。這個呼叫會擷取代表物件索引鍵的 ID。
JSONGenericDictExample.revive()
函數會使用這個 ID 來擷取並傳回私有靜態陣列中儲存的 JSONDictionaryExtnExample 物件。
import flash.display.MovieClip;
import flash.text.TextField;
var a_bob1:JSONGenericDictExample = new JSONGenericDictExample("Bob", new Date(Date.parse("01/02/1934")));
var a_bob2:JSONGenericDictExample = new JSONGenericDictExample("Bob", new Date(Date.parse("05/06/1978")));
var a_jen:JSONGenericDictExample = new JSONGenericDictExample("Jen", new Date(Date.parse("09/09/1999")));
var e = new JSONDictionaryExtnExample();
e[a_bob1] = {earnings: 40, violations: 2};
e[a_bob2] = {earnings: 10, violations: 1};
e[a_jen] = {earnings: 25, violations: 3};
trace("JSON.stringify(e): " + JSON.stringify(e)); // {"class JSONDictionaryExtnExample":
//{"id_class_JSONGenericDictExample_10001":
//{"earnings":10,"violations":1},
//"id_class_JSONGenericDictExample_10002":
//{"earnings":25,"violations":3},
//"id_class_JSONGenericDictExample_10000":
// {"earnings":40,"violations":2}}}
var e_result = JSON.stringify(e);
var e1 = new JSONDictionaryExtnExample();
var e2 = new JSONDictionaryExtnExample();
// It's somewhat easy to convert the string from JSON.stringify(e) back
// into a dictionary (turn it into an object via JSON.parse, then loop
// over that object's properties to construct a fresh dictionary).
//
// The harder exercise is to handle situations where the dictionaries
// themselves are nested in the object passed to JSON.stringify and
// thus does not occur at the topmost level of the resulting string.
//
// (For example: consider roundtripping something like
// var tricky_array = [e1, [[4, e2, 6]], {table:e3}]
// where e1, e2, e3 are all dictionaries. Furthermore, consider
// dictionaries that contain references to dictionaries.)
//
// This parsing (or at least some instances of it) can be done via
// JSON.parse, but it's not necessarily trivial. Careful consideration
// of how toJSON, replacer, and reviver can work together is
// necessary.
var e_roundtrip =
JSON.parse(e_result,
// This is a reviver that is focused on rebuilding JSONDictionaryExtnExample objects.
function (k, v) {
if ("class JSONDictionaryExtnExample" in v) { // special marker tag;
//see JSONDictionaryExtnExample.toJSON().
var e = new JSONDictionaryExtnExample();
var contents = v["class JSONDictionaryExtnExample"];
for (var i in contents) {
// Reviving JSONGenericDictExample objects from string
// identifiers is also special;
// see JSONGenericDictExample constructor and
// JSONGenericDictExample's revive() method.
e[JSONGenericDictExample.revive(i)] = contents[i];
}
return e;
} else {
return v;
}
});
trace("// == Here is an extended Dictionary that has been round-tripped ==");
trace("// == Note that we have revived Jen/Jan during the roundtrip. ==");
trace("e: " + e); //[JSONDictionaryExtnExample <Bob=[e=40,v=2], Bob=[e=10,v=1],
//Jen=[e=25,v=3]>]
trace("e_roundtrip: " + e_roundtrip); //[JSONDictionaryExtnExample <Bob=[e=40,v=2],
//Bob=[e=10,v=1], Jen=[e=25,v=3]>]
trace("Is e_roundtrip a JSONDictionaryExtnExample? " + (e_roundtrip is JSONDictionaryExtnExample)); //true
trace("Name change: Jen is now Jan");
a_jen.dname = "Jan"
trace("e: " + e); //[JSONDictionaryExtnExample <Bob=[e=40,v=2], Bob=[e=10,v=1],
//Jan=[e=25,v=3]>]
trace("e_roundtrip: " + e_roundtrip); //[JSONDictionaryExtnExample <Bob=[e=40,v=2],
//Bob=[e=10,v=1], Jan=[e=25,v=3]>]
社群成員 Todd Anderson 提供一份原生 JSON API 與協力廠商 as3corelib JSON 類別的比較。請參閱
