Ajax 기술을 기반으로 시험 카운트다운 구현 및 시험지 자동 제출

/**
* 构建XMLHttpRequest对象并请求服务器
* @param reqType：请求类型（GET或POST）
* @param url：服务器地址
* @param async：是否异步请求
* @param resFun：响应的回调函数
* @param parameter :请求参数
* @return :XMLHttpRequest对象
*/
function httpRequest(reqType,url,async,resFun,parameter){ 
var request = null;
if( window.XMLHttpRequest ){ //非IE浏览器，创建XMLHttpRequest对象
request = new XMLHttpRequest();
}else if( window.ActiveXObject ){ //IE浏览器，创建XMLHttpRequest对象
var arrSignatures = ["Msxml2.XMLHTTP", "Microsoft.XMLHTTP", "Microsoft.XMLHTTP", "MSXML2.XMLHTTP.5.0", "MSXML2.XMLHTTP.4.0", "MSXML2.XMLHTTP.3.0", "MSXML2.XMLHTTP"]; 
for( var i = 0; i < arrSignatures.length; i++ ){
request = new ActiveXObject( arrSignatures[i] );
if( request || typeof( request ) == "object" )
break;
}
}
if( request || typeof( request ) == "object" ){
if(reqType.toLowerCase()=="post"){ //以POST方式提交
request.open(reqType, url, true); //打开服务器连接
//设置MIME类型
request.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");
request.onreadystatechange = resFun; //设置处理响应的回调函数
parameter = encodeURI(parameter); //将参数字符串进行编码
request.send(parameter); //发送请求
}
else{ //以GET方式提交
url = url+"?"+parameter; 
request.open(reqType, url, true); //打开服务器连接
request.onreadystatechange = resFun; //响应回调函数
request.send(null); //发送请求
}
}
else{
alert( "该浏览器不支持Ajax！" );
} 
return request;
}

function showWindow(){ window.open('StartExam?action=startExam','','width=750,height=500,scrollbars=1');
}

<servlet>
<servlet-name>StartExam</servlet-name>
<servlet-class>com.lh.servlet.StartExam</servlet-class>
<init-param>
<param-name>examTime</param-name>
<param-value>20</param-value>
</init-param>
</servlet>

public void startExam(HttpServletRequest request,HttpServletResponse response)
throws ServletException,IOException{
HttpSession session = request.getSession();
request.setAttribute("time", examTime); //保存考试时间
session.setAttribute("startTime1",new Date().getTime()); //保存当前时间的毫秒数
request.getRequestDispatcher("startExam.jsp").forward(request, response);
}

<%@page contentType="text/html" pageEncoding="GBK"%>
${showStartTime}

<%@page contentType="text/html" pageEncoding="GBK"%>
${showRemainTime}

var request1= false;
var request2 = false;
//请求Servlet获得开始时间 
function showStartTime(){
var url = "StartExam";
//此处需要加&nocache="+new Date().getTime()，否则将出现时间不自动走动的情况
var parameter="action=showStartTime&nocache="+new Date().getTime();
request1 = httpRequest("post",url,true,callbackFunc,parameter); 
}
//回调函数 
function callbackFunc(){
if( request1.readyState==4 ){ 
if( request1.status == 200 ){
showStartTimep.innerHTML=request1.responseText;
}
}
}
//请求Servlet获得剩余时间 
function showRemainTime(){
var url = "StartExam";
var parameter="action=showRemainTime&nocache="+new Date().getTime();
request2 = httpRequest("post",url,true,callbackFunc_R,parameter); 
}
//回调函数 
function callbackFunc_R(){
if( request2.readyState==4 ){ 
if( request2.status == 200 ){
h=request2.responseText;
showRemainTimep.innerHTML=h;
h=h.replace(/\s/g,""); //去除字符串中的Unicode空白符
showRemainTimep.innerHTML=h;
if(h=="00:00:00"){
form1.submit();
}
}
}
}