前言：

本文内容：监听器GUI理解、Filter实现权限拦截

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监听器GUI理解

通过GUI理解

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package com.jokerdig.listener;

import java.awt.*;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;

/**
 * @author Joker大雄
 * @data 2022/4/11 - 13:18
 **/
public class TestPage {
    public static void main(String[] args) {
        Frame frame = new Frame("监听器的GUI理解");// 新建窗体
        Panel panel = new Panel(null);// 面板
        frame.setLayout(null);// 设置窗体布局

        frame.setBounds(300,300,500,500);
        frame.setBackground(new Color(0,123,211));

        panel.setBounds(50,50,200,200);
        panel.setBackground(new Color(183,0,122));
        //添加面板到窗体
        frame.add(panel);
        frame.setVisible(true); // 显示

        // 监听事件理解 一般不这样写
        /*
        frame.addWindowListener(new WindowAdapter() {
            @Override
            public void windowOpened(WindowEvent e) {
                System.out.println("窗口打开事件");
            }

            @Override
            public void windowClosing(WindowEvent e) {
                System.out.println("窗口关闭事件");
                //System.exit(0);
            }

            @Override
            public void windowClosed(WindowEvent e) {
                System.out.println("窗口关闭后事件");
            }

            @Override
            public void windowActivated(WindowEvent e) {
                System.out.println("窗口激活事件");
            }

            @Override
            public void windowDeactivated(WindowEvent e) {
                System.out.println("窗口未激活事件");
            }
        });
        */
        // 监听关闭事件 一般这样写
        frame.addWindowListener(new WindowAdapter() {
            @Override
            public void windowClosing(WindowEvent e) {
                System.out.println("关闭窗口");
                System.exit(0);
            }
        });
    }
}

Filter实现权限拦截

例如：用户登录后才能进入页面，注销后和未登录都不能进入页面

实现步骤

  • 用户登录后，向Session中放入用户数据
  • 进入主页的时候要判断用户是否已经登录 (用过滤器实现)

sys/initial.jsp

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<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>Title</title>
</head>
<body>
<h1>这是首页，只有用户登录的时候才能进入哦</h1>
<h2><a href="${pageContext.servletContext.contextPath}/servlet/logout">退出登录</a></h2>
</body>
</html>

login.jsp

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<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>Title</title>
</head>
<body>
    <form method="post" action="${pageContext.servletContext.contextPath}/servlet/login">
        账号：<input type="text" name="username"><br>
        密码：<input type="password" name="pwd"><br>
        <input type="submit">
    </form>
</body>
</html>

Web.xml

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<!--    配置登录-->
    <servlet>
        <servlet-name>login</servlet-name>
        <servlet-class>com.jokerdig.servlet.LoginServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>login</servlet-name>
        <url-pattern>/servlet/login</url-pattern>
    </servlet-mapping>
    <!--    配置退出-->
    <servlet>
        <servlet-name>logout</servlet-name>
        <servlet-class>com.jokerdig.servlet.LogoutServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>logout</servlet-name>
        <url-pattern>/servlet/logout</url-pattern>
    </servlet-mapping>
<!--    配置登录过滤器-->
    <filter>
        <filter-name>loginfilter</filter-name>
        <filter-class>com.jokerdig.filter.LoginFilter</filter-class>
    </filter>
    <filter-mapping>
        <filter-name>loginfilter</filter-name>
        <url-pattern>/sys/*</url-pattern>
    </filter-mapping>

LoginServlet.java

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package com.jokerdig.servlet;

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

/**
 * @author Joker大雄
 * @data 2022/4/11 - 13:39
 **/
public class LoginServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        // 获取前端请求参数
        String username = req.getParameter("username");
        String pwd = req.getParameter("pwd");
        if(username.equals("admin") && pwd.equals("123")){
            System.out.println("登录成功");
            req.getSession().setAttribute("USER_SESSION",req.getSession().getId());
            resp.sendRedirect("../sys/initial.jsp");
        } else {
            System.out.println("登录失败");
            resp.sendRedirect("../login.jsp");
        }
    }
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req,resp);
    }
}

LogoutServlet.java

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package com.jokerdig.servlet;

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

/**
 * @author Joker大雄
 * @data 2022/4/11 - 13:57
 **/
public class LogoutServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        Object user_session = req.getSession().getAttribute("USER_SESSION");
        if(user_session!=null){
            req.getSession().removeAttribute("USER_SESSION");
            resp.sendRedirect("../login.jsp");
        }
    }

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

LoginFilter.java

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package com.jokerdig.filter;

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

/**
 * @author Joker大雄
 * @data 2022/4/11 - 14:03
 **/
public class LoginFilter implements Filter {
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {

        // 未登录和注销后不能直接进入首页
        // ServletRequest  HttpServletRequest 转换
        HttpServletRequest req = (HttpServletRequest) request;
        HttpServletResponse resp = (HttpServletResponse) response;

        Object user_session = req.getSession().getAttribute("USER_SESSION");
        if(user_session==null){
            resp.sendRedirect("../login.jsp");
        }
        chain.doFilter(request,response);// 链
    }
    public void init(FilterConfig filterConfig) throws ServletException {

    }
    public void destroy() {
    }
}