Listener 快速开始

【SessionListener】

@WebListener
public class SessionListener implements HttpSessionListener,HttpSessionIdListener{
    @Override
    public void sessionIdChanged(HttpSessionEvent e, String oldSessionId) {
        SessionRegistry.updateSessionId(e.getSession(),oldSessionId);
        System.out.println(this.date()+":Session ID:"+oldSessionId+" changed to "+e.getSession().getId());
    }

    private String date() {
        SimpleDateFormat f = new SimpleDateFormat("EEE dd,mm,yyyy HH:mm:ss");
        return f.format(System.currentTimeMillis());
    }

    @Override
    public void sessionCreated(HttpSessionEvent e) {
        SessionRegistry.addSession(e.getSession());
        System.out.println(this.date() + ":Session "+e.getSession().getId()+"created.");
    }

    @Override
    public void sessionDestroyed(HttpSessionEvent e) {
        SessionRegistry.removeSession(e.getSession());
        System.out.println(this.date() + ":Session "+e.getSession().getId()+"destroyed.");
    }
}

【SessionRegistry】比较轻量，私有构造，一些静态方法

public final class SessionRegistry {
    private static final Map<String,HttpSession> SESSIONS = new Hashtable<>();
    public static void addSession(HttpSession session){
        SESSIONS.put(session.getId(),session);
    }
    public static void updateSessionId(HttpSession session,String oldSessionId){
        synchronized (SESSIONS){
            SESSIONS.remove(oldSessionId);
            addSession(session);
        }
    }

    public static void removeSession(HttpSession session){
        SESSIONS.remove(session.getId());
    }

    public static List<HttpSession> getAllSessions(){
        return new ArrayList<>(SESSIONS.values());
    }

    public static int getNumberOfSessions(){
        return SESSIONS.size();
    }
    private SessionRegistry(){}
}

【web.xml】

<listener>
    <listener-class>net.mypla.SessionListener</listener-class>
</listener>