监听器 listener

监听器的使用

1. 继承listener接口
2. 实现两个方法

demo1

public class Mylistener implements HttpSessionListener{


    public void sessionCreated(HttpSessionEvent httpSessionEvent) {

        ServletContext servletContext = httpSessionEvent.getSession().getServletContext();
        System.out.println("$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$");
        System.out.println(httpSessionEvent.getSession().getId());

        Integer onlineCount =(Integer) servletContext.getAttribute("count");

        if(onlineCount == null)
        {
            onlineCount = 1;
        }else {

            onlineCount++;
        }
        servletContext.setAttribute("count",onlineCount);
    }

    public void sessionDestroyed(HttpSessionEvent httpSessionEvent) {

        ServletContext servletContext = httpSessionEvent.getSession().getServletContext();
        Integer onlineCount =(Integer) servletContext.getAttribute("count");

        if(onlineCount == null)
        {
            onlineCount = 0;
        }else {

            onlineCount--;
        }

        servletContext.setAttribute("count",onlineCount);
    }

    }

注册监听器

    <listener>
        <listener-class>listener.Mylistener</listener-class>
    </listener>

demo2 GUI-WindowListener

public class ListenerGui {
    public static void main(String[] args) {
        Frame frame = new Frame("测试监听器");
        frame.setLayout(null);
        Panel panel = new Panel(null);

        frame.setBounds(100,100,500,500);
        frame.setBackground(new Color(0,255,0));

        panel.setBounds(50,50,200,150);
        panel.setBackground(new Color(0,0,255));

        frame.add(panel);
        frame.setVisible(true);

/*
        //窗口监听，适配器模式，可以不用实现所有方法
        frame.addWindowListener(new WindowAdapter() {
            @Override
            public void windowClosing(WindowEvent e) {
                System.out.println("关闭");
                System.exit(1);
            }
        });
*/
        
       //窗口监听
        frame.addWindowListener(new WindowListener() {
            public void windowOpened(WindowEvent e) {
                System.out.println("opened");
            }

            public void windowClosing(WindowEvent e) {
                System.out.println("closing");
                System.exit(1);

            }

            public void windowClosed(WindowEvent e) {
                System.out.println("closed");

            }

            public void windowIconified(WindowEvent e) {
                System.out.println("Iconified");

            }

            public void windowDeiconified(WindowEvent e) {
                System.out.println("Deiconified");

            }

            public void windowActivated(WindowEvent e) {
                System.out.println("Activated");

            }

            public void windowDeactivated(WindowEvent e) {
                System.out.println("Deactivated");

            }
        });
    }
}