java - 在 session 过期之前调用方法

Question

我的 webapp 有登录的用户。有一个超时。在 session 过期之前，我想执行一个方法来清除一些锁。

我已经实现了一个 sessionListener 但是一旦我到达 public void sessionDestroyed(HttpSessionEvent event) session 已经消失，我需要它的一些数据，所以我会喜欢在 session 实际过期之前执行一个方法(需要 session 处于 Activity 状态并且能够访问 FacesConfig.getCurrentInstance())。

我该怎么做？有任何想法吗？这是我的 session 监听器:

public class MySessionListener implements HttpSessionListener {

    private static final Logger log = LoggerFactory.getLogger(MySessionListener.class);

    public MySessionListener() {

    }

    public void sessionCreated(HttpSessionEvent event) {
        log.debug("Current Session created : "
              + event.getSession().getId()+ " at "+ new Date());
    }

    public void sessionDestroyed(HttpSessionEvent event) {
        // get the destroying session...

        HttpSession session = event.getSession();
        prepareLogoutInfoAndLogoutActiveUser(session);

        log.debug("Current Session destroyed :"
              + session.getId()+ " Logging out user...");

        /*
         * nobody can reach user data after this point because 
         * session is invalidated already.
         * So, get the user data from session and save its 
         * logout information before losing it.
         * User's redirection to the timeout page will be 
         * handled by the SessionTimeoutFilter.
         */

         // Only if needed
    }

    /**
     * Clean your logout operations.
     */
    public void prepareLogoutInfoAndLogoutActiveUser(HttpSession httpSession) {
        UserBean user = FacesContext.getCurrentInstance().getApplication().evaluateExpressionGet(FacesContext.getCurrentInstance(), "#{user}", UserBean.class);
        LockBean lock = FacesContext.getCurrentInstance().getApplication().evaluateExpressionGet(FacesContext.getCurrentInstance(), "#{lock}", LockBean.class);
        lock.unlock(user.getUsername());
        log.info("Unlocked examination for user: "+user.getUsername());
    }
}

但我在 FacesContext.getCurrentInstance().getApplication() 处得到了 NullPointerException 因为 getCurrentInstance 为空或 getApplication 返回 null

Answer 1

您可以通过实现 HttpSessionBindingListener 来实现，您需要通过调用 registerSession 注册一个持有锁的 session (字符串“sessionBindingListener”可能不会更改)。容器将在 session 超时之后和 session 被销毁之前回调valueUnbound()方法。

public class ObjectLock implements Serializable,HttpSessionBindingListener {
    public void valueBound(HttpSessionBindingEvent event) {
        log.info("valueBound:" + event.getName() + " session:" + event.getSession().getId() );

    }

    public void registerSession() {
        FacesContext.getCurrentInstance().getExternalContext().getSessionMap().put( "sessionBindingListener", this  );
        log.info( "registered sessionBindingListener"  );
    }

    public void valueUnbound(HttpSessionBindingEvent event) {
        log.info("valueUnBound:" + event.getName() + " session:" + event.getSession().getId() );
               // add you unlock code here:
        clearLocksForSession( event.getSession().getId() );
    }
}