关于登录过滤器

才开始做一部分，有一些问题

-Servlet

package com.imooc.web.servlet;

import java.io.IOException;
import java.util.List;

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 com.imooc.domain.User;
import com.imooc.service.UserService;
import com.imooc.service.impl.UserServiceImpl;

@WebServlet("/login")
public class LoginServlet extends HttpServlet {
	private static final long serialVersionUID = 1L;

	protected void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		// 接受数据
		String username = request.getParameter("username");
		String password = request.getParameter("password");
		// 封装数据
		User user = new User(username, password);
		// 处理数据：完成登录
		UserService userService = new UserServiceImpl();
		// 获得用户列表的集合
		List<User> userList = (List<User>) getServletContext().getAttribute("userList");
		User existUser = userService.login(userList, user);
		// jsp显示结果
		// 调用了login方法下面就是要判断了
		if (existUser == null) {
			// 登录失败
			request.setAttribute("msg", "用户名或密码错误！");
			request.getRequestDispatcher("/login.jsp").forward(request, response);
		} else {
			// 登录成功
			// 将用户信息保存
			request.getSession().setAttribute("existUser", existUser);
			response.sendRedirect(request.getContextPath() + "/categoryList.jsp");
		}
	}

	protected void doPost(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		doGet(request, response);
	}

}

-登录过滤器AuthFilter

package com.imooc.web.filter;

import java.io.IOException;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import com.imooc.domain.User;

public class AuthFilter implements Filter {

	public AuthFilter() {
	}

	public void destroy() {
	}

	public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
			throws IOException, ServletException {
		// 记得这里要强转一下request为它的子类HttpServletrequest，response同理
		HttpServletRequest req = (HttpServletRequest) request;
		HttpServletResponse res = (HttpServletResponse) response;

		// 获取唯一资源地址
		String uri = req.getRequestURI().toString();
		// 对后缀进行放行
		// 当查找到符合条件的字段时放行，然后返回
		if (uri.indexOf(".css") != -1 || uri.indexOf(".jpg") != -1 || uri.indexOf(".png") != -1
				|| uri.indexOf("login") != -1 || uri.indexOf(".js") != -1 || uri.indexOf("eckImg") != -1) {
			chain.doFilter(request, response);
			return;
		}

		// 对Session中是否有用户进行过滤
		// 先从Session域中获取一下
		User user = (User) req.getSession().getAttribute("existUser");
		// 判断一下是否为空，空字符串是否等于existUser，如果为空则说明还未登录，并转发回登录页面
		if (user == null || "".equals(user)) {
			// 未登录
			request.setAttribute("msg2", "用户未登录");
			res.sendRedirect(req.getContextPath() + "/login.jsp");
			return;
		} else {
			// 登录了就放行
			chain.doFilter(request, response);
			return;
		}

	}

	public void init(FilterConfig fConfig) throws ServletException {
	}

}

-xml配置

​<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xmlns="http://xmlns.jcp.org/xml/ns/javaee"
	xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd"
	id="WebApp_ID" version="3.1">
	<display-name>test_regist_login</display-name>
	<welcome-file-list>
		<welcome-file>index.html</welcome-file>
		<welcome-file>index.htm</welcome-file>
		<welcome-file>index.jsp</welcome-file>
		<welcome-file>default.html</welcome-file>
		<welcome-file>default.htm</welcome-file>
		<welcome-file>default.jsp</welcome-file>
	</welcome-file-list>

	<!-- 配置监听器 -->
	<listener>
		<listener-class>com.imooc.web.listener.InitServletContextListener</listener-class>
	</listener>

	<!-- 配置登录过滤器，/*代表拦截所有请求 -->
	<filter>
		<filter-name>AuthFilter</filter-name>
		<filter-class>com.imooc.web.filter.AuthFilter</filter-class>
	</filter>
	<filter-mapping>
		<filter-name>AuthFilter</filter-name>
		<url-pattern>/*</url-pattern>
	</filter-mapping>
</web-app>

-login.jsp

<%@ page language="java" contentType="text/html; charset=UTF-8"
	pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>登录</title>
<link rel="stylesheet" href="css/login.css">
</head>
<body>
	<div class="login">
		<div class="header">
			<h1>
				<a href="/login.do">登录</a>
				<p>${ msg }</p>
				<p>${ msg2 }</p>
			</h1>
			<button></button>
		</div>
		<form action="${pageContext.request.contextPath }/login" method="post">
			<div class="name">
				<input type="text" id="name" name="username">
				<p></p>
			</div>
			<div class="pwd">
				<input type="password" id="pwd" name="password">
				<p></p>
			</div>
			<div class="code">
				<input type="text" id="code" name="verifyCode" style="width: 150px">
				&nbsp;&nbsp;&nbsp;&nbsp; <img src="code.jpg"
					style="width: 150px; height: 42px; vertical-align: middle;">
				<p></p>
			</div>
			<div class="btn-red">
				<input type="submit" value="登录" id="login-btn">
			</div>
		</form>
	</div>
</body>
</html>

-显示图

老师请问我在登录过滤器里设置了msg2显示用户未登录，但为什么我在login页面什么都没输入点登录却出不来msg2的提示呢