剛在ajacn發(fā)了個(gè)貼，關(guān)于為XMLHttpRequest提供一個(gè)對(duì)象池?；蛟S能幫到你，轉(zhuǎn)貼如下：

在網(wǎng)上看到了有些同志提到了為Ajax的XMLHttpRequest提供一個(gè)對(duì)象池，也讀了他們給出的實(shí)現(xiàn)代碼。感覺(jué)不是特別理想，于是模仿apache的commons中的ObjectPool的思路寫(xiě)了一個(gè)簡(jiǎn)單的JavaScript版。 
望指教: 


代碼
function ObjectPool(poolableObjectFactory) {    
    this._poolableObjectFactory = poolableObjectFactory;    
    this._idlePool = [];     
    this._activePool = [];     
}    
// 從對(duì)象池中租借一個(gè)對(duì)象，如果目前沒(méi)有可用的空閑對(duì)象則通過(guò)poolableObjectFactory創(chuàng)建一個(gè)    
// 既然是借的，用完記得一定要還哦！    
ObjectPool.prototype.borrowObject = function() {    
    var object = null;    
    var idlePool = this._idlePool;    
    var factory = this._poolableObjectFactory;    
    if (idlePool.length > 0) {    
        object = idlePool.pop();    
    }    
    else {    
        object = factory.makeObject();    
    }    
    if (object != null) {    
        this._activePool.push(object);    
        if (factory.activateObject) {    
            factory.activateObject(object);    
        }    
    }    
    return object;    
}    
// 歸還一個(gè)對(duì)象    
ObjectPool.prototype.returnObject = function(object) {    
    function indexOf(array, object) {    
        for (var i = 0; i < array.length; i++) {    
            if (array[i] == object) return i;    
        }    
        return -1;    
    }    
    if (object != null) {    
        var activePool = this._activePool;    
        var factory = this._poolableObjectFactory;          
        var i = indexOf(activePool, object);    
        if (i < 0) return;          
        if (factory.passivateObject) {    
            factory.passivateObject(object);    
        }           
        activePool.splice(i, 1);    
        this._idlePool.push(object);    
    }    
}    
// 返回當(dāng)前激活對(duì)象的個(gè)數(shù)    
ObjectPool.prototype.getNumActive = function() {    
    return this._activePool.length;    
}    
// 返回當(dāng)前空閑對(duì)象的個(gè)數(shù)    
ObjectPool.prototype.getNumIdle = function() {    
    return this._idlePool.length;    
}    
// 銷毀對(duì)象池及其中的所有對(duì)象    
// 如果對(duì)象池中的對(duì)象需要析構(gòu)。那么必須實(shí)現(xiàn)poolableObjectFactory中的destroyObject方法，同時(shí)保證ObjectPool的destroy方法在需要的時(shí)候被調(diào)用到（例如Window的unload事件中）。    
ObjectPool.prototype.destroy = function() {    
    var factory = this._poolableObjectFactory;    
    function returnObject(object) {    
        if (factory.passivateObject) {    
            factory.passivateObject(object);    
        }    
    }    
    function destroyObject(object) {    
        if (factory.destroyObject) {    
            factory.destroyObject(object);    
        }    
    }       
    var activePool = this._activePool;    
    for (var i = 0; i < activePool.length; i++) {    
        var object = activePool[i];    
        returnObject(object);    
        destroyObject(object);    
    }    
    var idlePool = this._idlePool;    
    for (var i = 0; i < idlePool.length; i++) {    
        var object = idlePool[i];    
        destroyObject(object);    
    }    
    this._idlePool = null;     
    this._activePool = null;     
    this._poolableObjectFactory = null;    
}   

上面代碼中ObjectPool的構(gòu)造參數(shù)poolableObjectFactory的聲明如下: 

代碼
// 注意: 這只是說(shuō)明，不是真正的代碼！    
var PoolableObjectFactory = {           
    makeObject: function() {}, // 創(chuàng)建一個(gè)新的對(duì)象。(必須聲明)       

    activateObject: function(object) {}, // 當(dāng)一個(gè)對(duì)象被激活時(shí)(即被借出時(shí))觸發(fā)的方法。(可選)    

    passivateObject: function(object) {}, // 當(dāng)一個(gè)對(duì)象被鈍化時(shí)(即被歸還時(shí))觸發(fā)的方法。(可選)    

    destroyObject: function(object) {} // 銷毀一個(gè)對(duì)象。(可選)           
};    

結(jié)合XMLHttpRequest創(chuàng)建過(guò)程的簡(jiǎn)陋示例： 

代碼
// 聲明XMLHttpRequest的創(chuàng)建工廠    
var factory = {         
    makeObject: function() {    
        // 創(chuàng)建XMLHttpRequset對(duì)象    
        // 注：這里的創(chuàng)建方法不夠強(qiáng)壯，勿學(xué)！    
        if (window.ActiveXObject){    
            return new ActiveXObject("Microsoft.XMLHTTP");    
        }    
        else {    
            return new XMLHttpRequest();    
        }    
    },              
    passivateObject: function(xhr) {    
        // 重置XMLHttpRequset對(duì)象    
        xhr.onreadystatechange = {};    
        xhr.abort();    
    }    
};    
var pool = new ObjectPool(factory); // 創(chuàng)建對(duì)象池    
// ......    
var xhr = pool.borrowObject(); // 獲得一個(gè)XMLHttpRequest對(duì)象    
xhr.onreadystatechange = function() {    
    if (xhr.readyState == 4) {    
        // ......    
        pool.returnObject(xhr); // 歸還XMLHttpRequest對(duì)象    
    }    
};    
xhr.open(method, url, true);    
// ......    

最后附上jsUnit的測(cè)試用例: 

代碼
function test_pool() {    
    var factory = {    
        counter: 0,    

        makeObject: function() {    
            return {id: ++ this.counter};               
        },          

        activateObject: function(object) {    
            object.activated = true;    
        },    

        passivateObject: function(object) {    
            object.activated = false;               
        },    

        destroyObject: function(object) {    
            object.destroyed = true;                
        }    
    };    
    var pool = new ObjectPool(factory);    
    // borrowObject object1    
    var object1 = pool.borrowObject();    
    assertEquals(object1.id, 1);    
    assertTrue(object1.activated);    
    assertEquals(factory.counter, 1);    
    assertEquals(pool.getNumActive(), 1);    
    assertEquals(pool.getNumIdle(), 0);    
    // borrowObject object2    
    var object2 = pool.borrowObject();    
    assertEquals(object2.id, 2);    
    assertTrue(object2.activated);    
    assertEquals(factory.counter, 2);    
    assertEquals(pool.getNumActive(), 2);    
    assertEquals(pool.getNumIdle(), 0);    
    // borrowObject object3    
    var object3 = pool.borrowObject();    
    assertEquals(object3.id, 3);    
    assertTrue(object3.activated);    
    assertEquals(factory.counter, 3);    
    assertEquals(pool.getNumActive(), 3);    
    assertEquals(pool.getNumIdle(), 0);    
    // returnObject object2    
    pool.returnObject(object2);    
    assertFalse(object2.activated);    
    assertEquals(factory.counter, 3);    
    assertEquals(pool.getNumActive(), 2);    
    assertEquals(pool.getNumIdle(), 1);    
    // returnObject object3    
    pool.returnObject(object3);    
    assertFalse(object3.activated);    
    assertEquals(pool.getNumActive(), 1);    
    assertEquals(pool.getNumIdle(), 2);    
    // returnObject object1    
    pool.returnObject(object1);    
    assertFalse(object1.activated);    
    assertEquals(pool.getNumActive(), 0);    
    assertEquals(pool.getNumIdle(), 3);         
    // destroy the pool    
    pool.destroy();    
    assertTrue(object1.destroyed);    
    assertTrue(object2.destroyed);    
    assertTrue(object3.destroyed);    
}  

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