拦截器Filter

1.监听所有界面，防止非法访问，再根据url判断是否处理

package com.xxx.filter;

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

/**
 * 拦截非法访问index.jsp
 */
@WebFilter("/*")
public class fil2 implements Filter {
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {

    }

    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        //未登录跳入登录界面
        HttpServletRequest req=(HttpServletRequest)servletRequest;
        HttpServletResponse resp=(HttpServletResponse) servletResponse;

        //获取请求路径
        String url= req.getRequestURI();
        System.out.println(url);
        //放行登录界面(包括各种静态资源以及各种操作）
        if(url.contains("/login.jsp")){
            filterChain.doFilter(servletRequest,servletResponse);
            return;
        }
        if(url.contains("/js")||url.contains("/image")){
            filterChain.doFilter(servletRequest,servletResponse);
            return;
        }
        //跳转页面/pro/
        if(url.contains("/loginServlet")||url.equals("/pro/")){
            filterChain.doFilter(servletRequest,servletResponse);
            return;
        }
        //已经登录状态
        String uname=(String) req.getSession().getAttribute("uname");
        if(uname!=null){
            filterChain.doFilter(servletRequest,servletResponse);
            return;
        }

        resp.sendRedirect("login.jsp");


    }

    @Override
    public void destroy() {

    }
}

2.单个页面监听

package com.xxx.servlet;

import javax.servlet.ServletException;

import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

@WebServlet("/loginServlet")
public class Login extends HttpServlet {
    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        if(true){
            req.getSession().setAttribute("uname","uname");
            resp.sendRedirect("index.jsp");
        }else{
            req.getRequestDispatcher("login.jsp").forward(req,resp);
        }

    }
}

3.多个页面监听

@WebFilter(urlPatterns = { "/AddServlet","/qiantai/order.jsp","/RemoveServlet", "/UserOrderingServlet" })