// 用来在服务器端存储登录的所有帐号
public static List logonAccounts;

// 设置session不活动时间为30分
request.getSession().setMaxInactiveInterval(60*30);
if(logonAccounts==null){
logonAccounts = new ArrayList();
}
// 查看ArrayList中有没有该用户
for (int i = 0; i < logonAccounts.size(); i++) {
Account existAccount = (Account)logonAccounts.get(i);
if(account.getAccountId().equals(existAccount.getAccountId())){
return "denied";
}
}
// 在用户登录时，把sessionId添加到一个account对象中
// 在后面 ③ 需要根据此sessionId删除相应用户
account.setSessionId(request.getSession().getId());
// 该用户保存到ArrayList静态类变量中
logonAccounts.add(account);
return "login";

if(logonAccounts==null){
logonAccounts = new ArrayList();
}
// 删除ArrayList中的用户 ⑴
for (int i = 0; i < logonAccounts.size(); i++) {
Account existAccount = (Account)logonAccounts.get(i);
if(account.getAccountId().equals(existAccount.getAccountId())){
logonAccounts.remove(account);
}
}

function window.onbeforeunload(){
// 是否通过关闭按钮或者用Alt+F4退出
// 如果为刷新触发onbeforeunload事件，下面if语句不执行
if (event.clientX>document.body.clientWidth && event.clientY<0||event.altKey){
window.open('accountUnbound.jsp','',
'height=0,width=0,top=10000,left=10000');
}
}

<%
Account account = (Account) request.getSession().getAttribute("account");
if(account != null){
if(LoginAction.logonAccounts==null){
LoginAction.logonAccounts = new ArrayList();
}
// 删除ArrayList中的用户——下面代码和上面的 ⑴ 处一样
for (int i = 0; i < logonAccounts.size(); i++) {
Account existAccount = (Account)logonAccounts.get(i);
if(account.getAccountId().equals(existAccount.getAccountId())){
logonAccounts.remove(account);
}
}
}
%>

<script>
setTimeout("closeWindow();",3000);
function closeWindow(){
window.close();
}
</script>

public void sessionDestroyed(HttpSessionEvent event) {
// 取得不活动时的sessionId,并根据其删除相应logonAccounts中的用户
String sessionId = event.getSession().getId();
for (int i = 0; i < logonAccounts.size(); i++) {
Account existAccount = (Account)logonAccounts.get(i);
if(account.getSessionId().equals(existAccount.getSessionId())){
logonAccounts.remove(account);
}
}
}

<script>
// <![CDATA[
var http_request = false;
function makeRequest(url) {
http_request = false;
if (window.XMLHttpRequest) { // Mozilla, Safari,...
http_request = new XMLHttpRequest();
if (http_request.overrideMimeType) {
http_request.overrideMimeType('text/xml');
}
} else if (window.ActiveXObject) { // IE
try {
http_request = new ActiveXObject("Msxml2.XMLHTTP");
} catch (e) {
try {
http_request = new ActiveXObject("Microsoft.XMLHTTP");
} catch (e) {
}
}
}
if (!http_request) {
alert('Giving up :( Cannot create an XMLHTTP instance');
return false;
}
http_request.onreadystatechange = alertContents;
http_request.open('GET', url, true);
http_request.send(null);
}
function alertContents() {
if (http_request.readyState == 4) {
if (http_request.status == 200) {
window.close();
} else {
alert('There was a problem with the request.');
}
}
}
function window. onbeforeunload() {
makeRequest ('accountUnbound.jsp');
}
//]]>
</script>