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);
}

一页面多XMLHttpRequest对象

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