ajax请求

<script language="javascript" type="text/javascript"><!--
var ajaxRequest = null;
function getAjaxRequestObject() {
  try {
    // Firefox, Opera 8.0+, Safari
    ajaxRequest = new XMLHttpRequest();
  } catch (e) {
    // Internet Explorer
    try {
      ajaxRequest = new ActiveXObject("Msxml2.XMLHTTP");
    } catch (e) {
      ajaxRequest = new ActiveXObject("Microsoft.XMLHTTP");
    }
  }
  return ajaxRequest;
}
function ajaxRequest() {
  if (!ajaxRequest) {
    alert("ajax创建失败!");
    return false;
  }
  ajaxRequest.onreadystatechange = handleResponse;
  ajaxRequest.open("POST","JavaServlet.java",true);//第三个参数true为同步，false为异步
  ajaxRequest.send(null);
}
function handleResponse() {
  if (ajaxRequest.readyState == 4) { // handleResponse()方法会被调用4次，readyState的值从1到4，readyState == 4表示返回服务器响应
    if (ajaxRequest.status == 200) { // 请求成功
      alert("The server replied with:" + ajaxRequest.responseText); // responseText:服务器返回的String对象
    }
  }
}
--></script>