Ajax---001

• 创建xmlhttp对象

function ajaxFunction(){
            var xmlHttp;
            try {
                //firefox,opera,safari
                xmlHttp = new XMLHttpRequest();
            } catch (e) {
                try {
                    //Internet explore
                    xmlHttp = new ActiveXObject("Msxml2.XMLHTTP");
                } catch (e) {
                    try {
                        xmlHttp = new ActiveXObject("Microsoft.XMLHTTP");
                    } catch (e) {
                    }

                }
            }
            return xmlHttp;
        }

• 使用GET或POST方式不带参数时的访问方式

function func02(){
            var request = ajaxFunction();
            request.open("GET","servletURL",true);
            //request.open("POST","servletURL",true);
            request.send();
        }

•  使用POST方式带数据的访问方式

function func01(){
            //创建ajax对象
            var myrequest = ajaxFunction();

            //发送请求
            myrequest.open("POST","DemoServlet01",true);
            myrequest.setRequestHeader("Content-Type","application/x-www-form-urlencoded");
            myrequest.onreadystatechange = function(){
                if(myrequest.readyState == 4 && myrequest.status == 200){
                    alert(myrequest.responseText);
                }

            }
            myrequest.send("name=aliy&age=19");
        }

•  使用GET方式请求时可能得到的是缓存的结果，可以通过向url中添加唯一的uid来解决

xmlhttp.open("GET","demo_get.asp?t=" + Math.random(),true);
xmlhttp.send();