js请求servlet实现ajax请求的步骤详解

function sendRequestByGet(){
 //定义异步请求对象
 var xmlReq;
 //检测浏览器是否直接支持ajax
 if(window.XMLHttpRequest){//直接支持ajax
 xmlReq=new XMLHttpRequest();
 }else{//不直接支持ajax
 xmlReq=new ActiveObject('Microsoft.XMLHTTP');
 }
 
 //设置回调函数
 xmlReq.onreadystatechange=function(){
 if (xmlReq.readyState==4&&xmlReq.status==200) {
 //获取服务器的响应值
 var result=xmlReq.responseText;
 //后续操作
 alert(result);
 }
 };
 
 //创建异步get请求
 var url="Hello?name=zhangsan";
 xmlReq.open("GET",url,true);
 //发送请求
 xmlReq.send(null);
 }

function sendRequestByPost(){
 //定义异步请求对象
 var xmlReq;
 //检测浏览器是否直接支持ajax
 if(window.XMLHttpRequest){//直接支持ajax
 xmlReq=new XMLHttpRequest();
 }else{//不直接支持ajax
 xmlReq=new ActiveObject('Microsoft.XMLHTTP');
 }
 
 //设置回调函数
 xmlReq.onreadystatechange=function(){
 if (xmlReq.readyState==4&&xmlReq.status==200) {
 //获取服务器的响应值
 var result=xmlReq.responseText;
 //后续操作
 alert(result);
 }
 };
 
 //创建异步Post请求
 var url="Hello";
 xmlReq.open("POST",url,true);
 xmlReq.setRequestHeader("Content-Type","application/x-www-form-urlencoded");
 //发送请求
 var data="name=lisi";
 xmlReq.send(data);
 }

@Override
 protected void doPost(HttpServletRequest req, HttpServletResponse resp)
 throws ServletException, IOException {
 String name=req.getParameter("name");
 PrintWriter out = resp.getWriter();
 out.print(name);
 }