一页面多XMLHttpRequest对象

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 < 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 < 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); }

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