【Java】【学习】【监听器】Listener的学习的案例（窗体程序）

# JavaWeb 监听器listener 学习与简单应用

Java窗体程序使用监听器

效果：点击按钮，控制台出现文字

代码如下

import javax.swing.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.Date;

public class edu_Listener {
    public static void main(String[] args) {
        //创建窗口
        JFrame frame = new JFrame();
        //设置窗口大小
        frame.setSize(250,200);
        //设置窗口位置
        frame.setLocation(350,250);
        //创建按钮
        JButton btn = new JButton("Click");

        //创建监听器
        ActionListener listener = new ActionListener() {
            //处理事件的方法（事件处理器）
            @Override
            public void actionPerformed(ActionEvent e) {
                String dateStr = new Date(e.getWhen()).toString();
                System.out.println(dateStr);
                System.out.println("Hello world !");
            }
        };//注意这里的分号

        // 将监听器注册到按钮（此后监听器会一直处于监听按钮的状态）
        btn.addActionListener(listener);
        //将按钮添加到窗口
        frame.add(btn);
        //设置窗口显示状态
        frame.setVisible(true);
        System.out.println("执行完毕！");
    }
}

Javaweb 使用监听器

？ | 课件只写了一半

监听器类

类名：MyServletContextListener

代码：

import jakarta.servlet.*;
import jakarta.servlet.http.*;
import jakarta.servlet.annotation.*;

@WebListener
public class MyServletContextListener
        implements ServletContextListener, HttpSessionListener, HttpSessionAttributeListener {

    public MyServletContextListener() {
    }
//    在创建ServletContext对象时调用
    @Override
    public void contextInitialized(ServletContextEvent sce) {
        /* This method is called when the servlet context is initialized(when the Web application is deployed). */
    }
//    在销毁ServletContext对象时地调用
    @Override
    public void contextDestroyed(ServletContextEvent sce) {
        /* This method is called when the servlet Context is undeployed or Application Server shuts down. */
    }

    @Override
    public void sessionCreated(HttpSessionEvent se) {
        /* Session is created. */
    }

    @Override
    public void sessionDestroyed(HttpSessionEvent se) {
        /* Session is destroyed. */
    }

    @Override
    public void attributeAdded(HttpSessionBindingEvent sbe) {
        /* This method is called when an attribute is added to a session. */
    }

    @Override
    public void attributeRemoved(HttpSessionBindingEvent sbe) {
        /* This method is called when an attribute is removed from a session. */
    }

    @Override
    public void attributeReplaced(HttpSessionBindingEvent sbe) {
        /* This method is called when an attribute is replaced in a session. */
    }
}

web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
         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"
         version="4.0">
<!--    配置ServletContextListener生命周期监听器-->
    <listener>
    <listener-class>MyServletContextListener</listener-class>
    </listener>
</web-app>

[未完待续...]