/** 
* XMLHttpRequest Object Pool 
* 
* @author legend <legendsky@hotmail.com> 
* @link http://www.ugia.cn/?p=85 
* @Copyright www.ugia.cn 
*/ 
var XMLHttp = { 
	_objPool: [], 
	_getInstance: function () { 
		for (var i = 0; i < this._objPool.length; i ++){ 
			if (this._objPool[i].readyState == 0 || this._objPool[i].readyState == 4) { 
				return this._objPool[i]; 
			} 
		} 

		// IE5中不支持push方法 
		this._objPool[this._objPool.length] = this._createObj(); 
		return this._objPool[this._objPool.length - 1]; 
	}, 
	_createObj: function (){ 
		if (window.XMLHttpRequest){ 
			var objXMLHttp = new XMLHttpRequest(); 
		} 
		else { 
			var MSXML = ['MSXML2.XMLHTTP.5.0', 'MSXML2.XMLHTTP.4.0', 'MSXML2.XMLHTTP.3.0', 'MSXML2.XMLHTTP', 'Microsoft.XMLHTTP']; 
			for(var n = 0; n < MSXML.length; n ++){ 
				try { 
					var objXMLHttp = new ActiveXObject(MSXML[n]); 
					break; 
				} 
				catch(e) 
				{ 
				} 
			} 
		} 

		// mozilla某些版本没有readyState属性 
		if (objXMLHttp.readyState == null) { 
			objXMLHttp.readyState = 0; 
			objXMLHttp.addEventListener("load", function (){ 
														  objXMLHttp.readyState = 4; 
														  if (typeof objXMLHttp.onreadystatechange == "function"){ 
														  	objXMLHttp.onreadystatechange(); 
															} 
														}, false);
		}
		return objXMLHttp; 
	}, 

	// 发送请求(方法[post,get], 地址, 数据, 回调函数) 
	sendReq: function (method, url, data, callback){ 
		var objXMLHttp = this._getInstance(); 
		with(objXMLHttp){ 
			try{ 
				// 加随机数防止缓存 
				if (url.indexOf("?") > 0) { 
					url += "&randnum=" + Math.random(); 
				} 
				else { 
					url += "?randnum=" + Math.random(); 
				} 
				open(method, url, true); 
				
				// 设定请求编码方式 UTF-8
				setRequestHeader('Content-Type', 'application/x-www-form-urlencoded; charset=GB2312'); 
				send(data); 
				onreadystatechange = function () { 
					if (objXMLHttp.readyState == 4 && (objXMLHttp.status == 200 || objXMLHttp.status == 304)) { 
						callback(objXMLHttp); 
					} 
				} 
			} 
			catch(e){ 
				alert(e); 
			} 
		} 
	} 
};