第十一章从0-1搭建一个简单的JavaWeb系统（三）

一、工程代码结构

二、代码实现

三、运行效果

四、未完待续

本章节的每一段代码，建议全部自己敲一遍，加深印象，切勿直接复制黏贴。

一、工程代码结构

本章节实现注销（退出）功能，以下图片中标红的是新增的代码

二、代码实现

下图的SysFilter过滤器主要实现拦截访问的功能，对于用户访问页面时，Session中获取不到用户信息（即未登录）的情况进行拦截，重定向到Error页面（该页面可以再次连接到登录页面）。

package com.example.filter;

import com.example.pojo.User;

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

public class SysFilter implements Filter {
    public void init(FilterConfig config) throws ServletException {
    }

    public void destroy() {
    }

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws ServletException, IOException {
        HttpServletRequest httpServletRequest = (HttpServletRequest)request;
        HttpServletResponse httpServletResponse = (HttpServletResponse)response;
        HttpSession session = httpServletRequest.getSession();
        User user = (User)session.getAttribute("userSession");
        if (user == null) {
            httpServletResponse.sendRedirect((((HttpServletRequest) request).getContextPath() + "/error.jsp"));
        } else {
            chain.doFilter(request, response);
        }
    }
}

LogoutServlet接收用户的注销登录请求，具体实现是用户点击该页面的退出按钮时传递请求给LogoutServlet。

package com.example.servlet;

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;

public class LogoutServlet extends HttpServlet {

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

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        HttpSession session = request.getSession();
        session.removeAttribute("userSession");
        response.sendRedirect(request.getContextPath() + "/login.jsp");
    }
}

页面上的.../jsp/logout.do请求路径对应的是web.xml中配置的LogoutServlet请求路径：

web.xml中相较上一章节，增加了LogoutServlet和SysFilter：

<?xml version="1.0" encoding="UTF-8"?>
<web-app
    version="4.0"
    xmlns="http://xmlns.jcp.org/xml/ns/javaee"
    xmlns:javaee="http://xmlns.jcp.org/xml/ns/javaee"
    xmlns:xml="http://www.w3.org/XML/1998/namespace"
    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">
  <display-name>Archetype Created Web Application</display-name>
    <filter>
        <filter-name>CharacterEncodingFilter</filter-name>
        <filter-class>com.example.filter.CharacterEncodingFilter</filter-class>
    </filter>
    <filter-mapping>
        <filter-name>CharacterEncodingFilter</filter-name>
        <url-pattern>/*</url-pattern>
    </filter-mapping>
    <filter>
        <filter-name>SysFilter</filter-name>
        <filter-class>com.example.filter.SysFilter</filter-class>
    </filter>
    <filter-mapping>
        <filter-name>SysFilter</filter-name>
        <url-pattern>/jsp/*</url-pattern>
    </filter-mapping>
    <servlet>
        <servlet-name>LoginServlet</servlet-name>
        <servlet-class>com.example.servlet.LoginServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>LoginServlet</servlet-name>
        <url-pattern>/login.do</url-pattern>
    </servlet-mapping>
    <servlet>
        <servlet-name>LogoutServlet</servlet-name>
        <servlet-class>com.example.servlet.LogoutServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>LogoutServlet</servlet-name>
        <url-pattern>/jsp/logout.do</url-pattern>
    </servlet-mapping>
    <!-- 设置欢迎页面 -->
    <welcome-file-list>
        <welcome-file>/login.jsp</welcome-file>
    </welcome-file-list>
</web-app>

<%@ page language="java" contentType="text/html; charset=UTF-8"
         pageEncoding="UTF-8" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
    <title>无权限</title>
</head>
<body>

<p>
    请登录后再访问该页面！<a href="login.jsp" style="color: #0cde28" >返回</a>
</p>
<p>
    <img src="${pageContext.request.contextPath}/images/权限不够.png" alt="" align="middle" height="600px" width="1000px">
</p>

</body>
</html>