首先需要一个操作类：

Dao1：

package demoDao;
import java.awt.FlowLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.JButton;
import javax.swing.JFrame;

public class Dao1 {
    public static void main(String[] args) {
        JFrame jf = new JFrame();
        jf.setSize(300,200);
        jf.setLocation(200,200);
        jf.setLayout(new FlowLayout());
        jf.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        
        JButton btn = new JButton("确定");
        jf.add(btn);
        btn.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                System.out.println("hello!");
            }
        });
        
        jf.setVisible(true);
    }
}

这里创建了一个窗口和一个按钮。

下面就需要一个类去实现ServletContextListener然后在web.xml中注册：

AListener：

package demoListener;

import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;

public class AListener implements ServletContextListener {
    @Override
    public void contextInitialized(ServletContextEvent sce) {
        System.out.println("我来了！");
    }
    
    @Override
    public void contextDestroyed(ServletContextEvent sce) {
        System.out.println("我走了！");
    }
}

web.xml:

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns="http://xmlns.jcp.org/xml/ns/javaee"
    xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
    id="WebApp_ID" version="4.0">
    <display-name>day041501</display-name>
    <listener>
        <listener-class>demoListener.AListener</listener-class>
    </listener>
</web-app>