最近正在拜读<>这本书，运用书中知识，结合.net，写了这篇用.net 处理xmlHttp发送异步请求的文章。

我们要达到的目的是点击按钮，获得服务器的当前时间，aspx的html如下：
Html
<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="Default.aspx.cs" Inherits="Linkedu.Web.WebWWW.Default" %>

http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

http://www.w3.org/1999/xhtml" >










用Post方式获得服务器的当前时间

用Get方式获得服务器的当前时间

要用javascript 发送xmlHttp 请求必须解决的问题是跨浏览器的支持。我们把xmlHttp的发送封装在一个javascript对象中，同时在这个对象中解决了跨浏览器支持的问题。代码如下：

xmlHttp对象
/**//*
url-loading object and a request queue built on top of it
*/

/**//* namespacing object */
var net=new Object();

net.READY_STATE_UNINITIALIZED=0;
net.READY_STATE_LOADING=1;
net.READY_STATE_LOADED=2;
net.READY_STATE_INTERACTIVE=3;
net.READY_STATE_COMPLETE=4;

/**//*--- content loader object for cross-browser requests ---*/
net.xmlHttp=function(url, onload, params, method, contentType, onerror){
this.req=null;
this.onload=onload;
this.onerror=(onerror) ? onerror : this.defaultError;
if(typeof(method) == "undefined" || method == null)
{
method = "POST";
}
this.loadXMLDoc(url, params, method, contentType);
}

net.xmlHttp.prototype.loadXMLDoc=function(url, params, method, contentType){
if (!method){
method="GET";
}
if (!contentType && method=="POST"){
contentType='application/x-www-form-urlencoded';
}
if (window.XmlHttpRequest){
this.req=new XmlHttpRequest();
} else if (window.ActiveXObject){
this.req=new ActiveXObject("Microsoft.xmlHttp");
}
if (this.req){
try{
var loader=this;
this.req.onreadystatechange=function(){
net.xmlHttp.onReadyState.call(loader);
}
this.req.open(method,url,true);
if (contentType){
this.req.setRequestHeader('Content-Type', contentType);
}
this.req.send(params);
}catch (err){
this.onerror.call(this);
}
}
}

net.xmlHttp.onReadyState=function(){
var req=this.req;
var ready=req.readyState;
if (ready==net.READY_STATE_COMPLETE){
var httpStatus=req.status;
if (httpStatus==200 || httpStatus==0){
this.onload.call(this);
}else{
this.onerror.call(this);
}
}
}

net.xmlHttp.prototype.defaultError=function(){
alert("error fetching data!"
+"\n\nreadyState:"+this.req.readyState
+"\nstatus: "+this.req.status
+"\nheaders: "+this.req.getAllResponseHeaders());
}

下面开始写发送xmlHttp请求的代码：

default.js
//全局xmlHttp对象
var cobj;

/**//* Post begin*/
//绑定Post发送xmlHttp事件到btnTestPost
function loadTestPost()
{
var iobj = document.getElementById("btnTestPost");
//btnTestPost按钮监听的绑定
var clickRouter=new jsEvent.EventRouter(iobj,"onclick");
clickRouter.addListener(btnTestPostClick);
}
function btnTestPostClick()
{ // open参数 url, onload, params, method, contentType, onerror
cobj = new net.xmlHttp("DefaultHandler.ashx",dealResult, "", "POST");
}
/**//* Post end*/

/**//* Get begin*/
//绑定Get发送xmlHttp事件到btnTestGet
function loadTestGet()
{
var iobj = document.getElementById("btnTestGet");
//btnTestGet按钮监听的绑定
var clickRouter=new jsEvent.EventRouter(iobj,"onclick");
clickRouter.addListener(btnTestGetClick);
}
function btnTestGetClick()
{ // open参数 url, onload, params, method, contentType, onerror
cobj = new net.xmlHttp("DefaultHandler.ashx?T=1",dealResult, null, "GET");
}
/**//* Get end*/

function dealResult()
{
var dobj = document.getElementById("divResult");
dobj.innerHTML = cobj.req.responseXML.text;
}

window.onload = function()
{
//绑定Post发送xmlHttp事件到btnTestPost
loadTestPost();
//绑定Get发送xmlHttp事件到btnTestGet
loadTestGet();
};

最后是.net处理xmlHttp的代码
.net 处理xmlHttp请求
public class DefaultHandler : IHttpHandler
{
protected XmlDocument _xmlResult;

public void ProcessRequest(HttpContext context)
{
if (context.Request["T"] != null)
{//GET xmlhttp测试
context.Response.ContentType = "text/xml";
XmlDocument xmlDoc = new XmlDocument();
xmlDoc.LoadXml(string.Format(@"GET:{0}", System.DateTime.Now));
xmlDoc.Save(context.Response.OutputStream);
context.Response.End();
}
else
{//POST xmlhttp测试
context.Response.ContentType = "text/xml";
XmlDocument xmlDoc = new XmlDocument();
xmlDoc.Load(context.Request.InputStream);
if (xmlDoc.DocumentElement.Name == "T")
{
xmlDoc.LoadXml(string.Format(@"POST:{0}", System.DateTime.Now));
xmlDoc.Save(context.Response.OutputStream);
context.Response.End();
}
}
}

public bool IsReusable
{
get
{
return false;
}
}
}

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