一页面多XMLHttpRequest对象_javascript技巧

刚在ajacn发了个贴，关于为XMLHttpRequest提供一个对象池。或许能帮到你，转贴如下：

在网上看到了有些同志提到了为Ajax的XMLHttpRequest提供一个对象池，也读了他们给出的实现代码。感觉不是特别理想，于是模仿apache的commons中的ObjectPool的思路写了一个简单的JavaScript版。 
望指教: 


代码
function ObjectPool(poolableObjectFactory) {    
    this._poolableObjectFactory = poolableObjectFactory;    
    this._idlePool = [];     
    this._activePool = [];     
}    
// 从对象池中租借一个对象，如果目前没有可用的空闲对象则通过poolableObjectFactory创建一个    
// 既然是借的，用完记得一定要还哦！    
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;    
}    
// 归还一个对象    
ObjectPool.prototype.returnObject = function(object) {    
    function indexOf(array, object) {    
        for (var i = 0; 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         if (factory.passivateObject) {    
            factory.passivateObject(object);    
        }           
        activePool.splice(i, 1);    
        this._idlePool.push(object);    
    }    
}    
// 返回当前激活对象的个数    
ObjectPool.prototype.getNumActive = function() {    
    return this._activePool.length;    
}    
// 返回当前空闲对象的个数    
ObjectPool.prototype.getNumIdle = function() {    
    return this._idlePool.length;    
}    
// 销毁对象池及其中的所有对象    
// 如果对象池中的对象需要析构。那么必须实现poolableObjectFactory中的destroyObject方法，同时保证ObjectPool的destroy方法在需要的时候被调用到（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         var object = activePool[i];    
        returnObject(object);    
        destroyObject(object);    
    }    
    var idlePool = this._idlePool;    
    for (var i = 0; i         var object = idlePool[i];    
        destroyObject(object);    
    }    
    this._idlePool = null;     
    this._activePool = null;     
    this._poolableObjectFactory = null;    
}   

上面代码中ObjectPool的构造参数poolableObjectFactory的声明如下: 

代码
// 注意: 这只是说明，不是真正的代码！    
var PoolableObjectFactory = {           
    makeObject: function() {}, // 创建一个新的对象。(必须声明)       

    activateObject: function(object) {}, // 当一个对象被激活时(即被借出时)触发的方法。(可选)    

    passivateObject: function(object) {}, // 当一个对象被钝化时(即被归还时)触发的方法。(可选)    

    destroyObject: function(object) {} // 销毁一个对象。(可选)           
};    

结合XMLHttpRequest创建过程的简陋示例： 

代码
// 声明XMLHttpRequest的创建工厂    
var factory = {         
    makeObject: function() {    
        // 创建XMLHttpRequset对象    
        // 注：这里的创建方法不够强壮，勿学！    
        if (window.ActiveXObject){    
            return new ActiveXObject("Microsoft.XMLHTTP");    
        }    
        else {    
            return new XMLHttpRequest();    
        }    
    },              
    passivateObject: function(xhr) {    
        // 重置XMLHttpRequset对象    
        xhr.onreadystatechange = {};    
        xhr.abort();    
    }    
};    
var pool = new ObjectPool(factory); // 创建对象池    
// ......    
var xhr = pool.borrowObject(); // 获得一个XMLHttpRequest对象    
xhr.onreadystatechange = function() {    
    if (xhr.readyState == 4) {    
        // ......    
        pool.returnObject(xhr); // 归还XMLHttpRequest对象    
    }    
};    
xhr.open(method, url, true);    
// ......    

最后附上jsUnit的测试用例: 

代码
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);    
}