大家帮看看这是什么异常“Exception in thread "Timer-83" java.lang.NullPointerException”

Question

Exception in thread "Timer-83" java.lang.NullPointerException
at com.mchange.v2.log.log4j.Log4jMLog$Log4jMLogger.isLoggable(Log4jMLog.java:252)
at com.mchange.v2.resourcepool.BasicResourcePool$CheckIdleResourcesTask.run(BasicResourcePool.java:1342)
at java.util.TimerThread.mainLoop(Timer.java:512)
at java.util.TimerThread.run(Timer.java:462)

Answer 1

这个异常不是总出现，我是在过滤器文件中加入了几行代码才出现的，过滤器中的方法如下：
public void doFilter(ServletRequest request, ServletResponse response,
   FilterChain chain) throws IOException, ServletException {
  ((HttpServletResponse) response).setHeader("Cache-Control","no-store");       
  ((HttpServletResponse) response).setDateHeader("Expires",0);       
  ((HttpServletResponse) response).setHeader("Pragma","no-cache");
  if (ignore || (request.getCharacterEncoding() == null)) {
   request.setCharacterEncoding(selectEncoding(request));
  }
  chain.doFilter((HttpServletRequest)request, (HttpServletResponse)response);
//   chain.doFilter(request, response);
 }
方法中红色的三行代码是我后加入的。怎样才能防止上面的异常不再出现呢？各位再帮帮忙