今天想到用timer写一个定时清空session值得定时器，但报空指针。
代码如下：

    public  void removeYZM( HttpServletRequest request, String code) {
        Timer timer = new Timer();
        System.out.println("验证码：------"+request.getSession().getAttribute(code));
        timer.schedule(new TimerTask() {
            public void run() {
                // 删除session中存的验证码
                request.getSession().removeAttribute(code);
                timer.cancel();
            }
        }, 1 * 60 * 1000);
    }

报错信息

Exception in thread "Timer-1" java.lang.NullPointerException
    at com.temp.ssm.controller.UserClientController$1.run(UserClientController.java:51)
    at java.util.TimerThread.mainLoop(Timer.java:555)
    at java.util.TimerThread.run(Timer.java:505)