Ajax开发相关问题

1、关于XMLHttpRequest对象的建立（IE7上试验成功）。2008-3-21
<script language="JavaScript" type="text/JavaScript">
 
var xmlhttp_request = false;
try
{
   if (window.ActiveXObject)
   {
      for( var i = 20; i >= 0; i-- ) //如果是IE浏览器，则将XMLHttpRequest控件按版本从大到小生成。
      {
         try
         {
            if( i == 2 )
            {
                xmlhttp_request = new ActiveXObject( "Microsoft.XMLHTTP" );
            }
            else
            {
                xmlhttp_request = new ActiveXObject( "Msxml2.XMLHTTP." + i + ".0" );
            }
           // xmlhttp_request.setRequestHeader("Content-Type","text/xml"); //这两句加上就出错了
           // xmlhttp_request.setRequestHeader("Content-Type","gb2312");
            break;
        }
        catch(e)
        {
            xmlhttp_request = false;
        }
     }
  }
  else if (window.XMLHttpRequest)
  {
     xmlhttp_request = new XMLHttpRequest();
     if (xmlhttp_request.overrideMimeType)
     {
        xmlhttp_request.overrideMimeType('text/xml');
     }
   }
}
catch(e)
{
   xmlhttp_request = false;
}

if (!xmlhttp_request){
   alert("error initializing XMLHttpRequest!");
}

function getInfo(){
   alert("getInfo runing!");
   var phone = document.getElementById("phone").value;
   alert("xmlRequest is:" + xmlhttp_request );
   var url = "/StrutsSpring/index.jsp";
   xmlhttp_request.open("GET", url, true);
   xmlhttp_request.onreadystatechange = updatePage;
   xmlhttp_request.send(null);
}

function updatePage(){
   if (xmlhttp_request.readystate == 4)
       if (xmlhttp_request.status == 200)
           alert("server is done!");
        else if (xmlhttp_request.status == 404)
           alert("Request URL does not exist!");
        else
           alert("Request error code is " + xmlhttp_request.status);
}
</script>