var http_request = false;

	// 创建请求函数
	function create_request()
	{
		http_request = false;
		//开始初始化XMLHttpRequest对象
		if(window.XMLHttpRequest) { //Mozilla 浏览器
			http_request = new XMLHttpRequest();
			if (http_request.overrideMimeType) {//设置MiME类别
				http_request.overrideMimeType('text/xml');
			}
		}
		else if (window.ActiveXObject) { // IE浏览器
			try {
				http_request = new ActiveXObject("Msxml2.XMLHTTP");
			} catch (e) {
				try {
					http_request = new ActiveXObject("Microsoft.XMLHTTP");
				} catch (e) {}
			}
		}
		if (!http_request) { // 异常，创建对象实例失败
			window.alert("不能创建XMLHttpRequest对象实例.");
			return false;
		}
	}