過濾器（Filter）對登陸頁面進行過濾驗證

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 {
        //不進行登陸無法訪問其他頁面
        //ServletResponse類下面的子類HttpServletRequest中存在獲取路徑的方法getRequestURI
        //首先對req進行強轉
        HttpServletRequest request = (HttpServletRequest) req;
        //獲取路徑
        String uri = request.getRequestURI();
//如果路徑中存在這些就放行，注意：將jsp、css等路徑也進行過濾，不然頁面顯示不全
        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 {
            //獲取session，看用戶是否登陸
            HttpSession session = request.getSession();
            Object user = session.getAttribute("user");
            //登陸了進行放行操作
            if (user != null) {
                chain.doFilter(req, resp);

            } else {
                //沒有登陸過跳轉登錄頁面
                request.getRequestDispatcher("/login.jsp").forward(request, resp);
            }
        }

    }

    public void init(FilterConfig config) throws ServletException {

    }

}