（重點）JavaWeb（入門篇20）過濾器Filter實現對已註銷用戶強制訪問登錄後界面的攔截

一、過濾器Filter實現對已註銷用戶強制訪問登錄後界面的攔截

1.實現功能

實現用戶登錄後才能進入主頁，註銷後及時輸入主頁url也不能進入主頁

2. 核心代碼

在需要登錄的文件夾加一個過濾器

        HttpServletRequest request = (HttpServletRequest) servletRequest;
        if (request.getSession().getAttribute(Constant.USER_SESSION)==null){
            HttpServletResponse response = (HttpServletResponse) servletResponse;
            response.sendRedirect(request.getContextPath()+"/LogOff");
        }
        filterChain.doFilter(servletRequest,servletResponse);//轉發給其他過濾器或者Servlet

3.框架

4.代碼

登錄頁面login.jsp


<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>Login</title>
</head>
<body>
<h1>登錄界面login.jsp</h1>
<form action="<%=request.getContextPath()%>/Login" method="post">
    登錄名稱<input type="text" name="username" >
    <br>
    登錄密碼<input type="password" name="password">
    <br>
    <input type="submit" value="登錄">
</form>
</body>
</html>

2.實現登錄邏輯的Servlet ，Login.java

package com.bmft.loginInterception;

import com.bmft.util.Constant;

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

/**
 * 這個類是用戶在登錄界面
 * 點擊登錄後實現跳轉邏輯的Servlet
 */
public class Login extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        String username = req.getParameter("username");
        String password = req.getParameter("password");
        if (username == null || password == null){
            System.out.println("====登錄失敗null====");
            resp.sendRedirect("loginFailed.jsp");
        }
        else if (username.equals("root") && password.equals("123456")) {
            req.getSession().setAttribute(Constant.USER_SESSION, req.getSession().getId());
            System.out.println("====登錄成功====");
            resp.sendRedirect("sys/homePage.jsp");
        } else {
            System.out.println("====登錄失敗====");
            resp.sendRedirect("loginFailed.jsp");
        }
    }

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

3.登錄失敗的頁面 loginFailed.jsp

<%--
  Created by IntelliJ IDEA.
  User: 25301
  Date: 2020/6/19
  Time: 10:39
  To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>登錄失敗</title>
</head>
<body>
<h1>登錄失敗！</h1>
<h2>賬號或者密碼錯誤</h2>
<a href="login.jsp">重新登錄</a>
</body>
</html>

3.登錄成功進入主頁之前的過濾器LoginFilter.java

package com.bmft.filter;

import com.bmft.util.Constant;

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

/**
 * 過濾器步驟
 * 1.導包：到一個正確Servlet下的包，實現 Filter
 * 2.實現方法都Filter
 * （1）實現過濾
 * （2）釋放
 * 3.配置過濾器web.xml
 */
public class LoginFilter implements Filter {
    public void init(FilterConfig filterConfig) throws ServletException {
        System.out.println("=====過濾器LoginFilter初始化=====");
    }

    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        System.out.println("=====LoginFilter過濾開始=====");
        HttpServletRequest request = (HttpServletRequest) servletRequest;
        if (request.getSession().getAttribute(Constant.USER_SESSION)==null){
            HttpServletResponse response = (HttpServletResponse) servletResponse;
            response.sendRedirect(request.getContextPath()+"/LogOff");
        }
        filterChain.doFilter(servletRequest,servletResponse);//轉發給其他過濾器或者Servlet
        System.out.println("=====LoginFilter轉發完成，過濾結束======");
    }

    public void destroy() {
        System.out.println("====LoginFilter過濾器銷燬=====");
    }
}

4.登錄成功的主頁sys/ 目錄下的 homePage.jsp


<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>主頁</title>
</head>
<body>
<h1 style="color: aqua">登錄成功！這裏是主頁homePage</h1>
<h2>登錄成功！id = :<%=request.getSession().getId()%></h2>
<a href="<%=request.getContextPath()%>/LogOff">註銷登錄</a>
</body>
</html>

5.登錄主頁下點擊註銷執行的Servlet，LogOff.java

package com.bmft.loginInterception;

import com.bmft.util.Constant;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import java.io.IOException;

/**
 * 這個類在用戶的登錄成功進入主頁的
 * 時候點擊註銷登錄觸發  註銷操作，銷燬對應的 USER_SESSION 的值
 * 然後跳轉登錄頁面
 */
public class LogOff extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        req.getSession().setAttribute(Constant.USER_SESSION,null);
        resp.sendRedirect("login.jsp");
}
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}

6.編碼過濾器 Filter01.java 實現編碼的設置

package com.bmft.filter;

import javax.servlet.*;
import java.io.IOException;

/**
 * 過濾器步驟
 * 1.導包：到一個正確Servlet下的包，實現 Filter
 * 2.實現方法都Filter
 * （1）實現過濾
 * （2）釋放
 * 3.配置過濾器web.xml
 */
public class Filter01 implements Filter {
    public void init(FilterConfig filterConfig) throws ServletException {
        System.out.println("=====Filter01過濾器初始化=====");
    }

    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        System.out.println("=====Filter01過濾開始=====");
        servletRequest.setCharacterEncoding("utf-8");
        servletResponse.setCharacterEncoding("utf-8");
        servletResponse.setContentType("text/html;charset=UTF-8");
        filterChain.doFilter(servletRequest,servletResponse);//轉發給其他過濾器或者Servlet
        System.out.println("=====Filter01轉發完成，過濾結束======");
    }

    public void destroy() {
        System.out.println("====Filter01過濾器銷燬=====");
    }
}

7.web.xml的配置

  <!--Login Servlet映射-->
  <servlet>
    <servlet-name>Login</servlet-name>
    <servlet-class>com.bmft.loginInterception.Login</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>Login</servlet-name>
    <url-pattern>/Login</url-pattern>
  </servlet-mapping>
  <!--LogOff Servlet映射-->
  <servlet>
    <servlet-name>LogOff</servlet-name>
    <servlet-class>com.bmft.loginInterception.LogOff</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>LogOff</servlet-name>
    <url-pattern>/LogOff</url-pattern>
  </servlet-mapping>
    <!--編碼過濾-->
  <filter>
    <filter-name>Filter01</filter-name>
    <filter-class>com.bmft.filter.Filter01</filter-class>
  </filter>
  <filter-mapping>
    <filter-name>Filter01</filter-name>
    <url-pattern>/*</url-pattern>
  </filter-mapping>
  <!--登錄攔截過濾 sys 文件夾-->
  <filter>
    <filter-name>LoginFilter</filter-name>
    <filter-class>com.bmft.filter.LoginFilter</filter-class>
  </filter>
  <filter-mapping>
    <filter-name>LoginFilter</filter-name>
    <url-pattern>/sys/*</url-pattern>
  </filter-mapping>

5.頁面展示

1.登錄頁面login.jsp

2.錯誤登錄測試

3。返回重新登錄正確測試

4.不註銷的情況下複製登錄成功主頁鏈接，在另一個窗口打開

4.不註銷的情況下複製登錄成功主頁鏈接，在另一個瀏覽器（edge）打開

5.註銷後

刷新另一個窗口

二、錯誤與解決

1. 點擊登錄顯示404（相對路徑和絕對路勁的問題）

瞭解相對路徑和絕對路徑的區別使用

我的項目結構

1.絕對路徑
使用 /（反斜槓）會使用絕對路徑自動定義到 localhost:8080 目錄，而不是項目目錄，所以反斜槓一般配合項目路徑使用（例如）

<a href="<%=request.getContextPath()%>/LogOff">註銷登錄</a>

 response.sendRedirect(request.getContextPath()+"/LogOff");

2.相對路徑：
不適用反斜槓，就是相對路徑，定義到 http://localhost:8080/filter02_war 目錄（/filter02_war是你的項目）
相對路徑區別於絕對路徑（例如）

<a href="login.jsp">登錄</a>

resp.sendRedirect("login.jsp");

2.獲取的賬號密碼爲空

原因：使用req.getAttribute()獲取參數，應該是使用
req.getParameter(“password”);

（重點）JavaWeb（入門篇20）過濾器Filter實現對已註銷用戶強制訪問登錄後界面的攔截

一、過濾器Filter實現對已註銷用戶強制訪問登錄後界面的攔截

1.實現功能

2. 核心代碼

3.框架

4.代碼

5.頁面展示

二、錯誤與解決

1. 點擊登錄顯示404（相對路徑和絕對路勁的問題）

2.獲取的賬號密碼爲空

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