Day47-过滤器、监听器常见应用

过滤器、监听器常见应用

监听窗口：

package com.xiaozhao.listener;

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

/**
 * @author 小龚
 * @create 2022-09-08 9:47
 */
public class Test {
    public static void main(String[] args) {
        Frame frame = new Frame("中秋节快乐");//新建一个窗体
        Panel panel = new Panel(null);//面板
        frame.setLayout(null);//设置窗体的布局
        frame.setBounds(300,300,500,500);
        frame.setBackground(new Color(0,0,255));//设置背景颜色
        panel.setBounds(50,50,300,300);
        panel.setBackground(new Color(0,255,0));//设置背景颜色

        frame.add(panel);
        frame.setVisible(true);
        //监听事件，监听关闭事件
        frame.addWindowListener(new WindowListener() {
            @Override
            public void windowOpened(WindowEvent e) {
                System.out.println("打开");
            }

            @Override
            public void windowClosing(WindowEvent e) {
                System.out.println("关闭中");
            }

            @Override
            public void windowClosed(WindowEvent e) {
                System.out.println("已关闭");
            }

            @Override
            public void windowIconified(WindowEvent e) {

            }

            @Override
            public void windowDeiconified(WindowEvent e) {

            }

            @Override
            public void windowActivated(WindowEvent e) {
                System.out.println("激活");
                System.exit(0);
            }

            @Override
            public void windowDeactivated(WindowEvent e) {
                System.out.println("未激活");
            }
        });

    }
}
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测试

缩小化

用户登录之后才能进入主页！用户注销后就不能进入主页了！

1. 用户登录之后，向Session中放入用户的数据
2. 进入主页的时候要判断用户是否已经登录（在过滤器中实现）

代码实现：

控制器：

LoginOutServlet(控制注销)

package com.xiaozhao.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 小龚
 * @create 2022-09-08 22:39
 */
public class LoginOutServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        Object user_session = req.getSession().getAttribute("USER_SESSION");
        //如果user_session不为空，说明在登陆中
        if(user_session!=null){
            req.getSession().removeAttribute("USER_SESSION");//移除这个对象
            resp.sendRedirect(req.getContextPath()+"/login.jsp");//重定向到登录页面
        }
    }

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

package com.xiaozhao.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 小龚
 * @create 2022-09-08 21:49
 */
public class LoginServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //获取前端请求的参数
        String username = req.getParameter("username");
        if(username.equals("admin")){
            //登录成功
            req.getSession().setAttribute("USER_SESSION",req.getSession().getId());
            resp.sendRedirect(req.getContextPath()+"/sys/success.jsp");
        }
        else{
            //登录失败
            resp.sendRedirect(req.getContextPath()+"/error.jsp");
            //因为重定向的根目录是站点目录，因此要在路径前面加上当前web应用的路径：req.getContextPath()，不然就会出现404错误
        }
    }

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

SysFilter(用户登录之后才能进入主页)

package com.xiaozhao.filter;

import com.mysql.fabric.jdbc.FabricMySQLConnection;

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

/**
 * @author 小龚
 * @create 2022-09-08 23:10
 */
public class SysFilter implements Filter {
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {

    }

    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        //HttpServlet和Servlet不一样，需要强转
        HttpServletRequest req = (HttpServletRequest) servletRequest;
        HttpServletResponse resp = (HttpServletResponse) servletResponse;
        Object user_session = req.getSession().getAttribute("USER_SESSION");
        //如果user_session为空，说明没有登录成功，那就不能直接进入success.jsp界面
        if(user_session==null){
            resp.sendRedirect("../error.jsp");
        }
        filterChain.doFilter(servletRequest,servletResponse);//这句话必写，不然会在这里卡死
    }

    @Override
    public void destroy() {

    }
}
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视图：

错误页面：

<%@ page contentType="text/html;charset=UTF-8" language="java" %>


    


错误
没有权限，用户名错误
返回登录页面


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成功页面

<%@ page contentType="text/html;charset=UTF-8" language="java" %>


    


小赵欢迎你
注销


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登录页面

<%@ page contentType="text/html;charset=UTF-8" language="java" %>


    


登录

    
    



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web.xml设置

过滤器：

    <filter>
        <filter-name>SysFiltlerfilter-name>
        <filter-class>com.xiaozhao.filter.SysFilterfilter-class>
    filter>
    <filter-mapping>
        <filter-name>SysFiltlerfilter-name>
        <url-pattern>/sys/*url-pattern>
    filter-mapping>
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控制器

    <servlet>
        <servlet-name>LoginServletservlet-name>
        <servlet-class>com.xiaozhao.servlet.LoginServletservlet-class>
    servlet>
    <servlet-mapping>
        <servlet-name>LoginServletservlet-name>
        <url-pattern>/servlet/loginurl-pattern>
    servlet-mapping>
    <servlet>
        <servlet-name>LoginOutServletservlet-name>
        <servlet-class>com.xiaozhao.servlet.LoginOutServletservlet-class>
    servlet>
    <servlet-mapping>
        <servlet-name>LoginOutServletservlet-name>
        <url-pattern>/servlet/loginouturl-pattern>
    servlet-mapping>
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测试：

登录界面

登录成功界面

点击注销后再次访问成功页面

显示失败（过滤器的作用）