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JavaWeb之JSP 快递管理与过滤器详解

news 2025/9/23 12:36:34

JavaWeb之JSP 快递管理与过滤器详解

第一章 JSP 基础

1. JSP 初识

JSP（Java Server Pages）是 Sun 公司提出的基于 Java 技术的 Web 页面制作技术，允许在 HTML 文件中嵌入 Java 代码，简化动态内容生成。

主要作用：

生成动态页面，支持数据库查询、表单数据处理等
可与 Servlet 结合，实现复杂 Web 应用开发

核心特点：

简单性：通过嵌入 Java 代码简化动态内容编写
高效性：首次运行转换为 Servlet 并编译为字节码，支持 JIT 编译
多样化：支持 JSTL、EL 等标准标签库，简化常见开发需求

2. EL 表达式

EL(Expression Language) 旨在简化 JSP 代码编写，灵感源自 ECMAScript 和 XPath，语法结构为：${expression}

数据获取方式：

基础语法：${username}（依次从 Page、Request、Session、Application 域查找）
访问运算符：
- . 操作符：访问对象属性（如 ${user.name}）
- [] 操作符：访问数组或集合元素（如 ${list[0]}）

注意：EL 仅负责获取数据，无法循环遍历，且数据必须先存储到作用域中

案例代码：

<%@ page import="com.atguigu.pojo.SysUser" %><%--Created by IntelliJ IDEA.User: yutaoDate: 2025/2/19Time: 21:54To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head><title>EL表达式</title>
</head>
<body>
<%String name = "tom";int age = 18;SysUser sysUser = new SysUser();sysUser.setUsername("root");String[] strs = {"张三", "李四"};//将四个数据保存到请求域中request.setAttribute("sysname", name);request.setAttribute("sysage", age);request.setAttribute("sysuser", sysUser);request.setAttribute("strs", strs);//2.内置对象测试request.setAttribute("reqkey","request的数据");session.setAttribute("sessionkey","session的数据");application.setAttribute("applicationkey","application的数据");
%><h1>学生姓名:${sysname}</h1><h1>学生年龄:${sysage}</h1><h1>对象的姓名:${sysuser.username}</h1><h1>数组:${strs[0]},${strs[1]}</h1><h1>request:${reqkey}</h1><h1>session:${sessionkey}</h1><h1>application:${applicationkey}</h1>
</body>
</html>

3. JSTL 标签库

JSP 标准标签库（JSP Standard Tag Library，JSTL）提供了 Web 开发中常见的通用功能，包括迭代、条件判断、数据格式化等。

3.1 使用步骤

添加依赖包
（依赖包版本因 tomcat 环境和配置有所差异）

引入核心标签库

<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>

常用标签

<c:forEach> 标签属性：

属性	描述	是否必要	默认值
items	要被循环的信息	否	无
begin	开始的元素（0=第一个元素）	否	0
end	最后一个元素	否	Last element
step	每一次迭代的步长	否	1
var	代表当前条目的变量名称	否	无
varStatus	循环状态变量（index:索引；count:次数；first:是否首项；last:是否末项）	否	无

<c:if> 标签属性：

属性描述是否必要默认值
test 条件表达式是无
var 存储条件结果的变量否无
scope var属性的作用域否 page

属性	描述	是否必要	默认值
test	条件表达式	是	无
var	存储条件结果的变量	否	无
scope	var属性的作用域	否	page

案例代码：

<%@ page import="java.util.ArrayList" %><%--Created by IntelliJ IDEA.User: adminDate: 2025/2/25Time: 20:24To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<html>
<head><title>Title</title>
</head>
<body>
<%ArrayList<String> list = new ArrayList<>();list.add("张三");list.add("李四");list.add("王五");list.add("赵六");request.setAttribute("list", list);
%><table width="300px" border="1" cellspacing="0"><tr><td>序号</td><td>姓名</td></tr><c:if test="${list.size()>0}"><c:forEach items="${list}" var="element" varStatus="i"><tr ><td>${i.count}</td><td>${element}</td></tr></c:forEach></c:if></table>
</body>
</html>

JSP 四大域对象：

PageContext：页面域，作用于当前页面
request：请求域，作用于一次请求
session：会话域，作用于一次会话
application：应用域，作用于整个 Web 应用

当四大域存在同名 key 时，EL 表达式遵循从小到大的查找顺序（PageContext → request → session → application）

第二章案例开发 - 快递管理系统（第四期）

1. 动态展示快递记录信息

1.1 导入 JSTL 依赖

添加 JSTL 相关 jar 包到项目中（根据环境选择合适版本）

1.2 页面改造

将除 login.html 外的所有页面改为 JSP 动态页面，需包含：

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>

1.2.1 修改控制器跳转地址

@WebServlet("/deliverylist/list")
public class DeliveryListController extends HttpServlet {private DeliveryService deliveryService = new DeliveryServiceImpl();@Overrideprotected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {try {//1.解决请求乱码问题request.setCharacterEncoding("utf-8");response.setContentType("text/html;charset=utf-8");/*2.获取登录的用户id我们需要用登录用户的id去查询对应的快递信息也就是哪个用户登录,就只查询哪个用户相关的快递信息*/SysUser user = (SysUser) request.getSession().getAttribute("user");Integer userId = user.getId();List<Delivery> list = deliveryService.findAllDeliveryByUserId(userId);//3.将查询出来的集合响应给页面request.setAttribute("deliverylist", list);//这里将list.html改成list.jsprequest.getRequestDispatcher("/list.jsp").forward(request, response);} catch (SQLException e) {e.printStackTrace();}}@Overrideprotected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {doGet(request, response);}
}

1.2.2 修改 list.jsp 页面展示快递信息

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<html><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"><title>快递管理系统</title><meta name="Copyright" content="Douco Design." /><link href="css/public.css" rel="stylesheet" type="text/css"><script type="text/javascript" src="js/jquery.min.js"></script><script type="text/javascript" src="js/global.js"></script><script type="text/javascript" src="js/jquery.autotextarea.js"></script></head><body><div id="dcWrap"><div id="dcHead"><div id="head"><div class="logo"><a href="index.html"><img width="100px"height="25px" src="images/dclogo.gif"alt="logo"></a></div><div class="nav"><ul class="navRight"><li class="M noLeft"><ahref="JavaScript:void(0);">${user.username}</a><div class="drop mUser"><a href="password.html">修改密码</a></div></li><li class="noRight"><ahref="login.html">退出</a></li></ul></div></div></div><!-- dcHead 结束 --> <div id="dcLeft"><div id="menu"><ul class="top"><li><a href="index.html"><iclass="home"></i><em>管理首页</em></a></li></ul><ul><li><a href="password.html"><iclass="system"></i><em>修改密码</em></a></li><li><a href="list.html"><iclass="nav"></i><em>快递管理</em></a></li></ul></div></div><div id="dcMain"><!-- 当前位置 --><div id="urHere">快递管理系统<b>></b><strong>快递列表</strong> </div><div class="mainBox"style="height:auto!important;height:550px;min-height:550px;"><h3><a href="add.html"class="actionBtn add">添加快递</a>快递列表</h3><!-- 本阶段不实现筛选功能 --><div id="list"><table width="100%" border="0" cellpadding="8"cellspacing="0" class="tableBasic"><tr><th width="40" align="center">编号</th><th width="80" align="center">物流公司</th><th width="80" align="center">收件人</th><th width="80" align="center">手机号</th><th width="80" align="center">送达日期</th><th align="center">地址</th><th width="80" align="center">签收状态</th><th width="80" align="center">操作</th></tr><c:forEach items="${deliveryList}" var="delivery"><tr><td align="center">${delivery.id}</td><td>${delivery.company.companyName}</td><td align="center">${delivery.deliveryName}</td><td align="center">${delivery.phone}</td><td align="center">${delivery.sendTime}</td><td align="center">${delivery.address}</td><td align="center">${delivery.state==0?'未签收':'已签收'}</td><td align="center"><a href="#">编辑</a> | <a href="#">删除</a></td></tr></c:forEach></table></div><div class="clear"></div><div class="pager"> <a href="article.php?page=1">第一页</a><a href="article.php?page=1"> 上一页</a> <ahref="article.php?page=1">下一页</a> <ahref="article.php?page=1">最末页</a></div> </div></div><div class="clear"></div><div id="dcFooter"><div id="footer"><div class="line"></div><ul>版权所有 © 2024-2025 尚硅谷教育，并保留所有权利。</ul></div></div><!-- dcFooter 结束 --><div class="clear"></div> </div><script type="text/javascript">onload = function(){document.forms['action'].reset();}function douAction(){var frm = document.forms['action'];frm.elements['new_cat_id'].style.display = frm.elements['action'].value == 'category_move' ? '' : 'none';}</script></body>
</html>

2. 展示用户信息

修改登录相关页面（index.jsp / list.jsp / add.jsp / edit.jsp / password.jsp）为动态页面，展示登录用户信息。

2.1 修改登录控制器跳转

@WebServlet("/user/login")
public class UserLoginController extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {//1.设置请求参数编码格式req.setCharacterEncoding("UTF-8");resp.setContentType("text/html;charset=UTF-8");//2.获取请求参数String username = req.getParameter("username");String password = req.getParameter("password");System.out.println(username);//3.调用service层方法UserService userService = new UserServiceImpl();try {SysUser sysUser =userService.login(username,password);//System.out.println(sysUser);if (sysUser!=null){//保存登录的用户状态,用于查询登录快递信息以及登录的状态req.getSession().setAttribute("user",sysUser);req.getRequestDispatcher("/index.jsp").forward(req,resp);}else{req.getRequestDispatcher("/login.html").forward(req,resp);}} catch (SQLException e) {throw new RuntimeException(e);}}@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {doGet(req,resp);}
}

2.2 页面展示用户信息

<li class="M noLeft"><a href="JavaScript:void(0);">您好，${user.nickname}</a>

第三章修改密码功能

1. 通用页面抽取

1.1 创建资源文件

resource.jsp（CSS 和 JS 资源）

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<link href="/delivery_system/css/public.css" rel="stylesheet" type="text/css">
<script type="text/javascript" src="/delivery_system/js/jquery.min.js"></script>
<script type="text/javascript" src="/delivery_system/js/global.js"></script>
<script type="text/javascript" src="/delivery_system/js/jquery.autotextarea.js"></script>

head.jsp（头部和登录状态）

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<div id="dcHead"><div id="head"><div class="logo"><a href="index.html"><img width="100px"height="25px" src="/delivery_system/images/dclogo.gif"alt="logo"></a></div><div class="nav"><ul class="navRight"><li class="M noLeft"><ahref="JavaScript:void(0);">您好，${user.nickname}</a><div class="drop mUser"><a href="password.jsp">修改密码</a></div></li><li class="noRight"><ahref="login.php?rec=logout">退出</a></li></ul></div></div>
</div>

menu.jsp（左侧菜单）

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<div id="dcLeft"><div id="menu"><ul class="top"><li><a href="index.html"><iclass="home"></i><em>管理首页</em></a></li></ul><ul><li><a href="password.jsp"><iclass="system"></i><em>修改密码</em></a></li><li><a href="/delivery_system/delivery/list"><iclass="nav"></i><em>快递管理</em></a></li></ul></div>
</div>

1.2 页面引用

<head><jsp:include page="resource.jsp"></jsp:include>
</head>
<div id="dcWrap"><jsp:include page="head.jsp"></jsp:include><jsp:include page="menu.jsp"></jsp:include>

2. 密码修改功能实现

2.1 跳转密码修改页面

// 修改 menu.jsp 中的链接
<li><a href="/delivery_system/user/toPasswordPage"><iclass="system"></i><em>修改密码</em></a></li>     // 控制器代码
@WebServlet("/user/toPasswordPage")
public class UserToPasswordController extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {request.getRequestDispatcher("/password.jsp").forward(request,response);}@Overrideprotected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {doGet(request, response);}
}

2.2 密码修改控制器

@WebServlet("/user/changepassword")
public class UserChangePasswordController extends HttpServlet {private UserService userService = new UserServiceImpl();@Overrideprotected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {try {request.setCharacterEncoding("UTF-8");response.setContentType("text/html;charset=UTF-8");/*** 我们应该先根据当前登录的用户id查询对应的用户* 然后再service层拿出用户的密码,和我们在页面上* 填写的原始密码比较一样才能更新新密码*/SysUser sysUser = (SysUser) request.getSession().getAttribute("user");Integer uid = sysUser.getId();//获取页面上填写的原始密码和新密码String password = request.getParameter("password");String newpassword = request.getParameter("newpassword");//调用service层修改密码的方法,传递uid,和原始密码以及新密码boolean flag = userService.updateUserPassword(uid, password, newpassword);//判断将来如果flag为true,在页面展示"修改密码成功",否则展示"修改密码失败"if (flag == true) {request.setAttribute("message", "修改密码成功");request.getRequestDispatcher("/password.jsp").forward(request, response);} else {request.setAttribute("message", "修改密码失败");request.getRequestDispatcher("/password.jsp").forward(request, response);}} catch (SQLException e) {e.printStackTrace();}}@Overrideprotected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {doGet(request, response);}
}

2.3 Service 层实现

public interface UserService {/*** 用户登录* @param username* @param password* @return*/SysUser login(String username, String password) throws SQLException;/*** 修改用户密码* @param uid* @param password* @param newpassword* @return*/boolean updateUserPassword(Integer uid, String password, String newpassword) throws SQLException;
}public class UserServiceImpl implements UserService {private UserDao userDao = new UserDaoImpl();/*** 用户登录* @param username* @param password* @return*/@Overridepublic SysUser login(String username, String password) throws SQLException {//1.将password加密password = MD5Utils.encrypt(password);//2.将username和password传递到dao层SysUser sysUser = userDao.login(username,password);return sysUser;}@Overridepublic boolean updateUserPassword(Integer uid, String password, String newpassword) throws SQLException {//先根据当前登录的用户id查询对应的用户,以便拿出在数据库中用户的密码SysUser sysUser = userDao.findUserById(uid);String oldPassword = sysUser.getPassword();//将页面上获取的原始密码password加密然后和查询出来的密码比较password = MD5Utils.encrypt(password);if (oldPassword.equals(password)){userDao.updateUserPassword(uid,MD5Utils.encrypt(newpassword));return true;}return false;}
}

2.4 Dao 层实现

public interface UserDao {/*** 用户登录* @param username* @param password* @return*/SysUser login(String username, String password) throws SQLException;/*** 根据id查询用户* @param uid* @return*/SysUser findUserById(Integer uid) throws SQLException;/*** 修改用户密码* @param uid* @param newpassword*/void updateUserPassword(Integer uid, String newpassword) throws SQLException;
}public class UserDaoImpl implements UserDao {private QueryRunner qr = new QueryRunner(DruidUtils.getDataSource());/*** 用户登录* @param username* @param password* @return*/@Overridepublic SysUser login(String username, String password) throws SQLException {String sql = "select id,username,password,nickname from sys_user where username = ? and password = ?";SysUser sysUser = qr.query(sql, new BeanHandler<SysUser>(SysUser.class), username, password);return sysUser;}/*** 根据用户id查询用户* @param uid* @return* @throws SQLException*/@Overridepublic SysUser findUserById(Integer uid) throws SQLException {String sql = "select id,username,password,nickname from sys_user where id = ?";SysUser sysUser = qr.query(sql, new BeanHandler<>(SysUser.class), uid);return sysUser;}/*** 修改用户密码* @param uid* @param newpassword*/@Overridepublic void updateUserPassword(Integer uid, String newpassword) throws SQLException {String sql = "update sys_user set password = ? where id = ?";qr.update(sql,newpassword,uid);}
}

2.5 页面展示结果

<tr><td></td><td><input type="submit" name="submit" class="btn" value="提交" /></td>
</tr>
</table>
<div>${message}</div>
</form>

3. 用户退出功能

3.1 修改退出链接

<li class="noRight"><a href="/delivery_system/user/logout">退出</a></li>

3.2 退出控制器

@WebServlet("/user/logout")
public class UserLogoutController extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {request.getSession().invalidate();response.sendRedirect(request.getContextPath()+"/login.html");}@Overrideprotected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {doGet(request, response);}
}

第四章 Filter 过滤器

1. Filter 过滤器介绍

概述：过滤器是一个接口（Filter），实现该接口即可创建过滤器
作用：在请求到达 Web 资源之前进行过滤，决定是否放行请求
应用场景：
- 登录权限校验
- 统一处理请求中文乱码
- 敏感词过滤等

2. Filter 入门案例

2.1 单个过滤器实现

@WebServlet("/servlet1")
public class Servlet1 extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {response.getWriter().write("servlet1");}@Overrideprotected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {doGet(request, response);}
}public class Filter1 implements Filter {@Overridepublic void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {System.out.println("filter1");/*放行方法不写不放行写了放行不是递归调用*///filterChain.doFilter(servletRequest, servletResponse);}
}

XML 配置：

<filter><filter-name>filter1</filter-name><filter-class>com.atguigu.b_filter.Filter1</filter-class>
</filter>
<filter-mapping><filter-name>filter1</filter-name><!-- 访问该路径时触发过滤器 --><url-pattern>/servlet1</url-pattern>
</filter-mapping>

2.2 多个过滤器实现

@WebServlet("/servlet2")
public class Servlet2 extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {response.getWriter().write("servlet2");}@Overrideprotected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {doGet(request, response);}
}public class Filter2 implements Filter {@Overridepublic void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {System.out.println("filter2");filterChain.doFilter(servletRequest, servletResponse);}
}public class Filter3 implements Filter {@Overridepublic void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {System.out.println("filter3");filterChain.doFilter(servletRequest, servletResponse);}
}

XML 配置：

<filter><filter-name>filter2</filter-name><filter-class>com.atguigu.b_filter.Filter2</filter-class>
</filter>
<filter-mapping><filter-name>filter2</filter-name><url-pattern>/servlet2</url-pattern>
</filter-mapping><filter><filter-name>filter3</filter-name><filter-class>com.atguigu.b_filter.Filter3</filter-class>
</filter>
<filter-mapping><filter-name>filter3</filter-name><url-pattern>/servlet2</url-pattern>
</filter-mapping>

2.3 选择性拦截

@WebServlet("/servlet3")
public class Servlet3 extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {response.getWriter().write("servlet3");}@Overrideprotected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {doGet(request, response);}
}public class Filter4 implements Filter {@Overridepublic void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {System.out.println("filter4");// 根据条件决定是否放行// filterChain.doFilter(servletRequest, servletResponse);}
}

过滤器执行顺序：多个过滤器的执行顺序由 web.xml 中 filter-mapping 的配置顺序决定，先配置的先执行

    // 假设这里添加一个判断条件，满足条件才放行String value = servletRequest.getParameter("key");if ("allow".equals(value)) {filterChain.doFilter(servletRequest, servletResponse);} else {servletResponse.getWriter().write("Access denied");}
}

}


```xml
<filter><filter-name>filter4</filter-name><filter-class>com.atguigu.b_filter.Filter4</filter-class>
</filter>
<filter-mapping><filter-name>filter4</filter-name><url-pattern>/servlet3</url-pattern>
</filter-mapping>

5.Filter的生命周期

public class FilterLifeCycle implements Filter {// 1.初始化方法：服务器启动时执行，只执行一次@Overridepublic void init(FilterConfig filterConfig) throws ServletException {System.out.println("FilterLifeCycle初始化方法执行了");// 可以获取过滤器的初始化参数String encoding = filterConfig.getInitParameter("encoding");System.out.println("初始化参数encoding：" + encoding);}// 2.过滤方法：每次请求被过滤时执行，可执行多次@Overridepublic void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {System.out.println("FilterLifeCycle过滤方法执行了");filterChain.doFilter(servletRequest, servletResponse);}// 3.销毁方法：服务器关闭时执行，只执行一次@Overridepublic void destroy() {System.out.println("FilterLifeCycle销毁方法执行了");}
}

<filter><filter-name>filterLifeCycle</filter-name><filter-class>com.atguigu.b_filter.FilterLifeCycle</filter-class><!-- 配置初始化参数 --><init-param><param-name>encoding</param-name><param-value>UTF-8</param-value></init-param>
</filter>
<filter-mapping><filter-name>filterLifeCycle</filter-name><url-pattern>/*</url-pattern> <!-- 拦截所有请求 -->
</filter-mapping>

6.Filter的拦截路径配置

精确匹配：/servlet1 只拦截访问 /servlet1 的请求
目录匹配：/user/* 拦截所有以 /user 开头的请求（如 /user/login、/user/logout）
扩展名匹配：*.jsp 拦截所有 JSP 页面请求；*.html 拦截所有 HTML 页面请求
拦截所有：/* 拦截所有请求

7.Filter的应用场景1_登录权限校验

/*** 登录权限校验过滤器：未登录用户不能访问除登录页之外的资源*/
public class LoginFilter implements Filter {@Overridepublic void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {// 1.将ServletRequest转为HttpServletRequest（获取session需要）HttpServletRequest request = (HttpServletRequest) servletRequest;HttpServletResponse response = (HttpServletResponse) servletResponse;// 2.获取请求路径String requestURI = request.getRequestURI();System.out.println("请求路径：" + requestURI);// 3.排除不需要拦截的资源（登录页、登录请求、静态资源等）if (requestURI.contains("/login.html") || requestURI.contains("/user/login") || requestURI.contains("/css/") || requestURI.contains("/js/") || requestURI.contains("/images/")) {// 放行filterChain.doFilter(request, response);return;}// 4.判断用户是否登录（从session中获取用户信息）SysUser user = (SysUser) request.getSession().getAttribute("user");if (user != null) {// 已登录，放行filterChain.doFilter(request, response);} else {// 未登录，重定向到登录页response.sendRedirect(request.getContextPath() + "/login.html");}}
}

<filter><filter-name>loginFilter</filter-name><filter-class>com.atguigu.c_filter.LoginFilter</filter-class>
</filter>
<filter-mapping><filter-name>loginFilter</filter-name><url-pattern>/*</url-pattern> <!-- 拦截所有请求 -->
</filter-mapping>

8.Filter的应用场景2_统一处理中文乱码

/*** 统一处理请求和响应的中文乱码过滤器*/
public class EncodingFilter implements Filter {@Overridepublic void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {// 1.转为HttpServletRequest和HttpServletResponseHttpServletRequest request = (HttpServletRequest) servletRequest;HttpServletResponse response = (HttpServletResponse) servletResponse;// 2.处理POST请求的中文乱码request.setCharacterEncoding("UTF-8");// 3.处理响应的中文乱码response.setContentType("text/html;charset=UTF-8");// 4.放行filterChain.doFilter(request, response);}
}

<filter><filter-name>encodingFilter</filter-name><filter-class>com.atguigu.c_filter.EncodingFilter</filter-class>
</filter>
<filter-mapping><filter-name>encodingFilter</filter-name><url-pattern>/*</url-pattern> <!-- 拦截所有请求 -->
</filter-mapping>

注意：对于GET请求的中文乱码，Tomcat 8及以上版本已经默认处理（使用UTF-8编码），如果是低版本Tomcat，需要在Server.xml中配置URIEncoding="UTF-8"

9.Filter链的执行顺序

当多个过滤器同时拦截同一个资源时，执行顺序由web.xml中filter-mapping的配置顺序决定：先配置的先执行。

例如：

<!-- 先执行FilterA -->
<filter-mapping><filter-name>filterA</filter-name><url-pattern>/servlet</url-pattern>
</filter-mapping><!-- 后执行FilterB -->
<filter-mapping><filter-name>filterB</filter-name><url-pattern>/servlet</url-pattern>
</filter-mapping>

执行流程：FilterA.doFilter() → FilterB.doFilter() → Servlet → FilterB.doFilter()之后的代码 → FilterA.doFilter()之后的代码

10.使用注解配置Filter

除了在web.xml中配置Filter，还可以使用@WebFilter注解进行配置：

@WebFilter(urlPatterns = "/*", initParams = {@WebInitParam(name = "encoding", value = "UTF-8")})
public class AnnotationFilter implements Filter {@Overridepublic void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {System.out.println("注解配置的过滤器执行了");filterChain.doFilter(servletRequest, servletResponse);}
}

注意：使用注解配置多个Filter时，执行顺序由类名的字母顺序决定（不推荐，建议使用web.xml控制顺序）。

第五章.总结

JSP：动态网页开发技术，可嵌入Java代码，最终会被转换为Servlet执行。
EL表达式：简化JSP中数据的获取，语法${表达式}，从四大域中获取数据。
JSTL标签库：提供通用功能标签（如c:forEach循环、c:if条件判断），需导入依赖并在JSP中声明。
Filter过滤器：
- 实现Filter接口，重写doFilter方法。
- 作用：登录权限校验、统一编码处理等。
- 配置方式：web.xml或@WebFilter注解。
- 执行顺序：由filter-mapping的配置顺序决定。