过滤器实现权限过滤

我会带着你远行 2021-07-24 20:21 454阅读 0赞

**目录**

一 需求

二 实战

--------------------

# 一 需求 #

用户登录后才能进入主页，用户注销后不能进入主页。

# 二 实战 #

1 定义常量

package com.cakin.constant;
    
    
    /**
    * @ClassName: Constant
    * @Description: 常量类
    * @Date: 2020/6/16
    * @Author: cakin
    */
    public class Constant {
        /**
         * 保存用户Session
         */
        public static final String USER_SESSION = "USER_SESSION";
    }

2 定义权限过滤器

package com.cakin.filter;
    
    
    import javax.servlet.Filter;
    import javax.servlet.FilterConfig;
    import javax.servlet.ServletException;
    import javax.servlet.ServletRequest;
    import javax.servlet.ServletResponse;
    import javax.servlet.FilterChain;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
    import java.io.IOException;
    
    
    import static com.cakin.constant.Constant.USER_SESSION;
    
    
    /**
    * @ClassName: SysFilter
    * @Description: 实现用户登录后才能进入主页，用户注销后不能进入主页。
    * @Date: 2020/6/16
    * @Author: cakin
    */
    public class SysFilter implements Filter {
        public void init(FilterConfig filterConfig) throws ServletException {
    
    
        }
    
    
        /**
         * 功能描述：用户权限过滤器
         *
         * @param req   请求
         * @param res   响应
         * @param chain 过滤器链
         * @throws IOException      IOException
         * @throws ServletException ServletException
         * @author cakin
         * @date 2020/6/16
         */
        public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain) throws IOException, ServletException {
            // 需要先转换一下
            HttpServletRequest request = (HttpServletRequest) req;
            HttpServletResponse response = (HttpServletResponse) res;
    
    
            Object attribute = request.getSession().getAttribute(USER_SESSION);
            // 通过USER_SESSION判断用户是否登录
            if (attribute == null) {
                response.sendRedirect("/login.jsp");
            }
            chain.doFilter(request, res);
        }
    
    
        public void destroy() {
    
    
        }
    }

3 定义登录Servlet

package com.cakin.servlet;
    
    
    import javax.servlet.ServletException;
    import javax.servlet.http.HttpServlet;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
    import java.io.IOException;
    
    
    import static com.cakin.constant.Constant.USER_SESSION;
    
    
    /**
    * @ClassName: LoginServlet
    * @Description: 登录Servlet
    * @Date: 2020/6/16
    * @Author: cakin
    */
    public class LoginServlet extends HttpServlet {
        /**
         * 功能描述：用户登录逻辑
         *
         * @author cakin
         * @date 2020/6/16
         * @param req 请求
         * @param resp 响应
         * @throws IOException IOException
         */
        @Override
        protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws IOException {
            String username = req.getParameter("username");
    
    
            if (username.equals("admin")) {
                req.getSession().setAttribute(USER_SESSION, req.getSession().getId());
                // 登录成功登录到首页
                resp.sendRedirect("/sys/home.jsp");
            } else {
                // 登录失败重定向到错误页面
                resp.sendRedirect("/error.jsp");
            }
        }
    
    
        @Override
        protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
            doGet(req, resp);
        }
    }

4 定义注销Servlet

package com.cakin.servlet;
    
    
    import javax.servlet.ServletException;
    import javax.servlet.http.HttpServlet;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
    import java.io.IOException;
    
    
    import static com.cakin.constant.Constant.USER_SESSION;
    
    
    /**
    * @ClassName: logout
    * @Description: 注销
    * @Date: 2020/6/16
    * @Author: cakin
    */
    public class Logout extends HttpServlet {
        /**
         * 功能描述：用户注销逻辑
         *
         * @author cakin
         * @date 2020/6/16
         * @param req 请求
         * @param resp 响应
         * @throws IOException IOException
         */
        @Override
        protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws IOException {
            Object attribute = req.getSession().getAttribute(USER_SESSION);
            if (attribute != null) {
                // session失效
                req.getSession().removeAttribute(USER_SESSION);
            }
            // 重定向到登录页
            resp.sendRedirect("/login.jsp");
        }
    
    
        @Override
        protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
            doGet(req, resp);
        }
    }

5 主页

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
    <html>
    <head>
        <title>Title</title>
    </head>
    <body>
    <h1>主页</h1>
    <a href="/servlet/logout">注销</a>
    </body>
    </html>

6 错误页

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
    <html>
    <head>
        <title>Title</title>
    </head>
    <body>
    <h1>错误</h1>
    <h3>没有权限，用户名错误</h3>
    <a href="/login.jsp">返回登录页</a>
    </body>
    </html>

7 登录页

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
    <html>
    <head>
        <title>Title</title>
    </head>
    <body>
        <h1>登录</h1>
        <form action="/servlet/login" method="post">
            <input type="text" name="username">
            <input type="submit">
        </form>
    </body>
    </html>

8 web.xml 配置

<?xml version="1.0" encoding="UTF-8"?>
    <web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
             xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
             xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
             version="4.0">
        <servlet>
            <servlet-name>ShowServlet</servlet-name>
            <servlet-class>com.cakin.servlet.ShowServlet</servlet-class>
        </servlet>
        <servlet-mapping>
            <servlet-name>ShowServlet</servlet-name>
            
            <url-pattern>/servlet/show</url-pattern>
        </servlet-mapping>
        <servlet-mapping>
            <servlet-name>ShowServlet</servlet-name>
            <url-pattern>/show</url-pattern>
            
        </servlet-mapping>
    
    
        
        <servlet>
            <servlet-name>LoginServlet</servlet-name>
            <servlet-class>com.cakin.servlet.LoginServlet</servlet-class>
        </servlet>
        <servlet-mapping>
            <servlet-name>LoginServlet</servlet-name>
            <url-pattern>/servlet/login</url-pattern>
        </servlet-mapping>
    
    
        
        <servlet>
            <servlet-name>Logout</servlet-name>
            <servlet-class>com.cakin.servlet.Logout</servlet-class>
        </servlet>
        <servlet-mapping>
            <servlet-name>Logout</servlet-name>
            <url-pattern>/servlet/logout</url-pattern>
        </servlet-mapping>
    
    
        
        <filter>
            <filter-name>SysFilter</filter-name>
            <filter-class>com.cakin.filter.SysFilter</filter-class>
        </filter>
        <filter-mapping>
            <filter-name>SysFilter</filter-name>
            <url-pattern>/sys/*</url-pattern>
        </filter-mapping>
        
        
        <filter>
            <filter-name>EncodingFilter</filter-name>
            <filter-class>com.cakin.filter.CharacterEncodingFilter</filter-class>
        </filter>
        <filter-mapping>
            <filter-name>EncodingFilter</filter-name>
            
            <url-pattern>/servlet/*</url-pattern>
        </filter-mapping>
    </web-app>