Ajax的基本用法

客戶端js：

<script type="text/javascript">
function testBack(){
//建立對象
var req;
if(window.XMLHTTPRequest){
req = new XMLHttpRequest();
}else if(window.ActiveXObject){
req = new ActiveXObject("Msxml2.XMLHTTP");
}
//建立請求 請求方式 請求路徑  同步/異步
req.open("post","HelloBack",true);
//監聽響應信息
req.onreadystatechange = function(){
if(req.readyState==4){
if(req.status==200){
//var result = req.responseText;
//eval("var user = "+result);
//alert(user.uname);
//eval("var users = "+result);
//alert(users[2].realname);
var result  = req.responseXML;
alert(result.getElementsByTagName("uname")[0].firstChild.data);
}
}
}
//發送請求
req.setRequestHeader("Content-Type","application/x-www-form-urlencoded");
req.send(null);
}
</script>

servlet：

public class HelloBack extends HttpServlet {


@Override
protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
resp.setCharacterEncoding("utf-8");
//第一種普通文本
//resp.setContentType("text/html;charset=utf-8");
//resp.getWriter().print("普通文本");
//Json格式數據
//resp.setContentType("text/html;charset=utf-8");
//resp.getWriter().print("[{uname:'zhangsan',realname:'張三三1'},{uname:'zhangsan',realname:'張三三2'},{uname:'zhangsan',realname:'張三三3'}]");
//XML格式的數據 返回數據的格式必需要正確
resp.setContentType("text/xml;charset=utf-8");
resp.getWriter().print("<user><uname>zhangsan</uname></user>");
}
}