会话过期前调用方法

Question

我的webapp有登录的用户。有超时。在会话到期之前，我想执行一种方法来清除一些锁。

我已经实现了一个，sessionListener但是一旦到达public void sessionDestroyed(HttpSessionEvent event)会话，会话就已经消失了，我需要从中获取一些数据，因此我想FacesConfig.getCurrentInstance()在会话实际过期之前执行一个方法（该会话需要运行并可以访问）。

我怎样才能做到这一点？有任何想法吗？这是我的会话监听器：

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());
    }
}

但我要去NullPointerException的FacesContext.getCurrentInstance().getApplication()原因getCurrentInstance是null或getApplication返回null

Answer 1

您可以通过实现HttpSessionBindingListener来实现，您需要通过调用来注册一个持有锁的会话registerSession（字符串“
sessionBindingListener”可能不会更改）。valueUnbound()在会话超时之后和会话被销毁 之前 ，容器将回调该方法。

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() );
    }
}