var http_request = false;

function send_request(method,url,content,responseType,callback) {
	http_request = false;
	if(window.XMLHttpRequest) {
		http_request = new XMLHttpRequest();
		if (http_request.overrideMimeType) {
			http_request.overrideMimeType("text/xml");
		}
	}
	else if (window.ActiveXObject) {
		try {
			http_request = new ActiveXObject("Msxml2.XMLHTTP");
		} catch (e) {
			try {
				http_request = new ActiveXObject("Microsoft.XMLHTTP");
			} catch (e) {}
		}
	}
	if (!http_request) {
		window.alert("不能创建XMLHttpRequest对象实例.");
		return false;
	}
	if(responseType.toLowerCase()=="text") {
		http_request.onreadystatechange = callback;
	}
	else if(responseType.toLowerCase()=="xml") {
		http_request.onreadystatechange = callback;
	}
	else {
		window.alert("响应类别参数错误");
		return false;
	}

	if(method.toLowerCase()=="get") {

		http_request.open(method, url, true);
                http_request.setRequestHeader("If-Modified-Since","0");
	}
	else if(method.toLowerCase()=="post") {
		http_request.open(method, url, true);
		http_request.setRequestHeader("Content-Type","application/x-www-form-urlencoded");
	}
	else {
		window.alert("http请求类别参数错误");
		return false;
	}
	http_request.send(content);
}