過濾器實現權限過濾

目錄

一 需求

二 實戰

---

一 需求

用戶登錄後才能進入主頁，用戶註銷後不能進入主頁。

二 實戰

1 定義常量

package com.cakin.constant;


/**
* @ClassName: Constant
* @Description: 常量類
* @Date: 2020/6/16
* @Author: cakin
*/
public class Constant {
    /**
     * 保存用戶Session
     */
    public static final String USER_SESSION = "USER_SESSION";
}

2 定義權限過濾器

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: 實現用戶登錄後才能進入主頁，用戶註銷後不能進入主頁。
* @Date: 2020/6/16
* @Author: cakin
*/
public class SysFilter implements Filter {
    public void init(FilterConfig filterConfig) throws ServletException {


    }


    /**
     * 功能描述：用戶權限過濾器
     *
     * @param req   請求
     * @param res   響應
     * @param chain 過濾器鏈
     * @throws IOException      IOException
     * @throws ServletException ServletException
     * @author cakin
     * @date 2020/6/16
     */
    public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain) throws IOException, ServletException {
        // 需要先轉換一下
        HttpServletRequest request = (HttpServletRequest) req;
        HttpServletResponse response = (HttpServletResponse) res;


        Object attribute = request.getSession().getAttribute(USER_SESSION);
        // 通過USER_SESSION判斷用戶是否登錄
        if (attribute == null) {
            response.sendRedirect("/login.jsp");
        }
        chain.doFilter(request, res);
    }


    public void destroy() {


    }
}

3 定義登錄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: 登錄Servlet
* @Date: 2020/6/16
* @Author: cakin
*/
public class LoginServlet extends HttpServlet {
    /**
     * 功能描述：用戶登錄邏輯
     *
     * @author cakin
     * @date 2020/6/16
     * @param req 請求
     * @param resp 響應
     * @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());
            // 登錄成功登錄到首頁
            resp.sendRedirect("/sys/home.jsp");
        } else {
            // 登錄失敗重定向到錯誤頁面
            resp.sendRedirect("/error.jsp");
        }
    }


    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}

4 定義註銷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: 註銷
* @Date: 2020/6/16
* @Author: cakin
*/
public class Logout extends HttpServlet {
    /**
     * 功能描述：用戶註銷邏輯
     *
     * @author cakin
     * @date 2020/6/16
     * @param req 請求
     * @param resp 響應
     * @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);
        }
        // 重定向到登錄頁
        resp.sendRedirect("/login.jsp");
    }


    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}

5 主頁

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

6 錯誤頁

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>Title</title>
</head>
<body>
<h1>錯誤</h1>
<h3>沒有權限，用戶名錯誤</h3>
<a href="/login.jsp">返回登錄頁</a>
</body>
</html>

7 登錄頁

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>Title</title>
</head>
<body>
    <h1>登錄</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>
        <!--這個路徑會走到下面配置的過濾器-->
        <url-pattern>/servlet/show</url-pattern>
    </servlet-mapping>
    <servlet-mapping>
        <servlet-name>ShowServlet</servlet-name>
        <url-pattern>/show</url-pattern>
        <!--這個路徑不會走到下面配置的不會走過濾器-->
    </servlet-mapping>


    <!--登錄Servlet-->
    <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>


    <!--註銷Servlet-->
    <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>


    <!--權限檢查過濾器-->
    <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>
    
    <!--解決中文亂碼過濾器-->
    <filter>
        <filter-name>EncodingFilter</filter-name>
        <filter-class>com.cakin.filter.CharacterEncodingFilter</filter-class>
    </filter>
    <filter-mapping>
        <filter-name>EncodingFilter</filter-name>
        <!-- /servlet請求都會走這個過濾器-->
        <url-pattern>/servlet/*</url-pattern>
    </filter-mapping>
</web-app>