public void doFilter(ServletRequest request, ServletResponse response,
        FilterChain chain) throws IOException, ServletException {

    HttpServletRequest httpRequest = (HttpServletRequest)request;
    HttpServletResponse httpResponse = (HttpServletResponse) response;
    HttpSession session = httpRequest.getSession();
    if(session.getAttribute(ApplicationSource.USER) == null
            && !httpRequest.getRequestURI().endsWith("/login.jsp") // 这些都是一些需要排除的页面
              && !httpRequest.getRequestURI().endsWith("/calendar/")
            && (httpRequest.getRequestURI().indexOf("/calendar/img") < 0)
            && (httpRequest.getRequestURI().indexOf("/calendar/resources") < 0)
            && (httpRequest.getRequestURI().indexOf("/calendar/servlet") < 0)
            && !httpRequest.getRequestURI().endsWith("/login.do")){
        httpResponse.sendRedirect(httpRequest.getContextPath() + "/login.jsp");
    }    
    chain.doFilter(request, response);
}