ajax使用

/** ajax的使用*/
function displayMessage(){
	var ajaxUrl="toPlay!getTopTwoAssetBean.action"; //ajax访问的地址
	rtspAjax = new AJAX_OBJ(ajaxUrl,responseFunction); //调用我们ajax.js中的代码 responseFunction为ajax回调函数
 	rtspAjax.errorhandle=RequestError;    //调用ajax异常时,处理函数
  	rtspAjax.requestData();
}

 /**处理ajax请求返回数据*/
function responseFunction(){
	var txt = rtspAjax.getText(); 
	alert(txt);   //打印出ajax请求的内容
}
/**处理ajax请求失败函数*/
function RequestError(){
	alert("获取数据超时,请检查网络");
}

?ajax.js

/*============================================AJAX 对象==================================
* 作用：通过get或post的方式请求异步（同步）数据
* @param{string} url: 将要去请求的路径
* @param{function} callback: 回调函数，即请求成功时所做的操作，带一个参数：new XMLHttpRequest()的返回值 
* @param{boolean} asyn: 是否异步调用，默认为true:异步，反之同步调用
* @param{number} timer: 请求失败时，隔timer时间重新请求一次
* @param{number} retrieval: 请求失败时，重新请求的次数，当为 -1 时，表示无数次
* @param{function} errorhandle: 请求失败时，所做的处理
*/
var objPool = [];
objPool[0] = createXMLHttpRequest();
objPool[1] = createXMLHttpRequest();
objPool[2] = createXMLHttpRequest();
objPool[3] = createXMLHttpRequest();
objPool[4] = createXMLHttpRequest();
objPool[5] = createXMLHttpRequest();

function AJAX_OBJ(url, callback, asyn, timer, retrieval, errorhandle){
	this.num = 0;
	this.url = url;
	this.urlParameters = "";
	this.callback = callback;
	this.errorhandle = errorhandle || this.errorHandle;
	this.timer = timer || 20000;
	this.timeout = -1;
	this.retrieval = retrieval || 1;	
	this.asyn = typeof asyn =="undefined"?true:asyn;
	this.xmlHttp = this.getInstance();
	this.backParam = null;
	this.timerout;
}
//请求实例
AJAX_OBJ.prototype.getInstance = function(){
	/*var xmlh = null;
	xmlh = new XMLHttpRequest();
	return xmlh;*/
	for (var i = 0; i < objPool.length; i ++)
	{
		if ( objPool[i].readyState == 4||objPool[i].readyState == 0)
		{
			return objPool[i];
		}
	}
	objPool[objPool.length] = createXMLHttpRequest();
	return objPool[objPool.length - 1];
}

function createXMLHttpRequest(){
	var xmlh = null;
	if(window.XMLHttpRequest){
		xmlh = new XMLHttpRequest();
	}else if(window.ActiveXObject){
		xmlh = new ActiveXObject("Microsoft.XMLHTTP");
	}
	return xmlh;
}
//用GET方式请求数据
AJAX_OBJ.prototype.requestData = function(){
	var request_url = this.url + this.urlParameters;
	var self = this;
	this.xmlHttp.onreadystatechange = function(){
		self.stateChanged();
	};
	this.xmlHttp.open("GET", request_url, this.asyn);
	this.xmlHttp.send(null);
	
}
//用POST方式请求数据
AJAX_OBJ.prototype.requestDataPost = function() {
	this.xmlHttp.open("POST", this.url, this.asyn);
	var self = this;
	this.xmlHttp.onreadystatechange = function() {
		self.stateChanged();
	}
	this.xmlHttp.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
	this.xmlHttp.setRequestHeader("Content-length", this.urlParameters.length);
	this.xmlHttp.setRequestHeader("Connection", "close");
	this.xmlHttp.send(this.urlParameters);
	return 0;
}

//请求数据的处理
AJAX_OBJ.prototype.stateChanged = function(){
	var self=this;
	if(this.xmlHttp.readyState == 2) this.timerout=setTimeout(function(){self.check()}, this.timer);
	if(this.xmlHttp.readyState == 4){
		if(this.xmlHttp.status == 200){
			clearTimeout(this.timerout);
			if(this.backParam == null) this.callback(this.xmlHttp);
			else this.callback(this.xmlHttp,this.backParam);
		}
	}
}

AJAX_OBJ.prototype.check = function(){
	if(this.xmlHttp.readyState!=4||(this.xmlHttp.readyState==4&&this.xmlHttp.status!=200))
		this.errorhandle(this.xmlHttp.status);
}

//请求失败的处理
AJAX_OBJ.prototype.errorHandle = function(params){
	shsowTip("请求失败");
}
//参数的处理
AJAX_OBJ.prototype.addParameter = function(params,type){
	this.type =  typeof(type)=="undefined"?0:type;
	if(this.type == 0){
		if(params.length > 0){
			this.urlParameters = "";
			for(var i = 0; i < params.length; i++){
				var curr_param = params[i];
				if(i == 0) this.urlParameters += "?" + curr_param.name + "=" + curr_param.value;
				else t