过滤器（Filter）对登陆页面进行过滤验证

import javax.servlet.*;
import javax.servlet.annotation.WebFilter;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpSession;
import java.io.IOException;

@WebFilter("/*")
public class LoginFilter implements Filter {
    public void destroy() {
    }

    public void doFilter(ServletRequest req, ServletResponse resp, FilterChain chain) throws ServletException, IOException {
        //不进行登陆无法访问其他页面
        //ServletResponse类下面的子类HttpServletRequest中存在获取路径的方法getRequestURI
        //首先对req进行强转
        HttpServletRequest request = (HttpServletRequest) req;
        //获取路径
        String uri = request.getRequestURI();
//如果路径中存在这些就放行，注意：将jsp、css等路径也进行过滤，不然页面显示不全
        if (uri.contains("login.jsp")
                || uri.contains("/loginServlet")
                || uri.contains("/checkCodeServlet")
                || uri.contains("/css/")
                || uri.contains("/fonts/")
                || uri.contains("/img/")
                || uri.contains("/js/")
                ) {
            //放行
            chain.doFilter(req, resp);


        } else {
            //获取session，看用户是否登陆
            HttpSession session = request.getSession();
            Object user = session.getAttribute("user");
            //登陆了进行放行操作
            if (user != null) {
                chain.doFilter(req, resp);

            } else {
                //没有登陆过跳转登录页面
                request.getRequestDispatcher("/login.jsp").forward(request, resp);
            }
        }

    }

    public void init(FilterConfig config) throws ServletException {

    }

}