@WebFilter("*.jsp")
public class FilterTest1 implements Filter {
public void destroy() {
}

public void doFilter(ServletRequest req, ServletResponse resp, FilterChain chain) throws ServletException, IOException {
    //判断是否已经登录了，如果没有登录就需要跳转到登录界面，但是如果访问的资源路径本来
    //就是登录页面，那么就不需要拦截了，这里需要进行判断排除

    //记得强制转型
    HttpServletRequest request = (HttpServletRequest)req ;

    //获取session对象，看看对应的属性是否有值
    HttpSession session = request.getSession();
    Object  login = session.getAttribute("login");

    //获取url路径，看看里面是否是登录资源相关的
    String requestURI = request.getRequestURI();

    //在过滤掉登录相关时，一定要排除一些js，css文件
    if (login != null || requestURI.contains("/longin.jsp") || requestURI.contains("/css/") ||
            requestURI.contains("/js/") || requestURI.contains(https://www.xxe.io/) ) {
        chain.doFilter(req, resp);
    } else {
        request.getRequestDispatcher("/longin.jsp").forward(request, resp);
    }
}

public void init(FilterConfig config) throws ServletException {

}

}