监听器和监听器过滤器常见应用GUl中理解

实现一个监听器的接口：（有N种）

1.编写一个监听器

实现监听器的接口

//统计网上在线人数：统计Session

public class olinejqt implements HttpSessionListener {

//创建session监听：看你的一举一动

//一旦创建Session就会触发这个事件

public void sessionCreated(HttpSessionEvent se) {

ServletContext ctx = se.getSession ().getServletContext ();

System.out.println (se.getSession ().getId ());

Integer inter = (Integer) ctx.getAttribute ("session");

//判断inter为空就是没有人

if (inter==null){

//加人

inter = new Integer (1); //1人

}else{

int count = inter.intValue ();

inter = new Integer (count+1);//+1=2人

}

ctx.setAttribute ("session",inter);

}

//销毁Session监听

//一旦销毁Session就会触发这一事件

public void sessionDestroyed(HttpSessionEvent se) {

ServletContext ctx = se.getSession ().getServletContext ();

Integer inter = (Integer) ctx.getAttribute ("session");

//判断inter为空就是没有人

if (inter==null){

//加人

inter = new Integer (0); //0人没人了

}else{

int count = inter.intValue ();

inter = new Integer (count-1);//-1

}

ctx.setAttribute ("session",inter);

}

/**

*Session销毁

* 1.手动销毁 getSession() invalidate()

* 2.自动销毁

}

2.在web中配置监听器

<listener-class>com.bubbles.filter.jtqlistener.olinejqt</listener-class>

</listener>

3.看情况是否使用

监听器和监听器GUl中理解

过滤器、监听器常见应用

监听器：GUl编程中经常使用

package com.bubbles.filter.Server;import java.awt.*;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
import java.awt.event.WindowListener;public class TestPane1 {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 () {public void windowOpened(WindowEvent e) {System.out.println ("打开");}public void windowClosing(WindowEvent e) {System.out.println ("关闭ing");System.exit (0);}public void windowClosed(WindowEvent e) {System.out.println ("关闭ed");}public void windowIconified(WindowEvent e) {}public void windowDeiconified(WindowEvent e) {}public void windowActivated(WindowEvent e) {System.out.println ("激活");}public void windowDeactivated(WindowEvent e) {System.out.println ("未激活");}});}
}
用户登录之后才能进入首页 ！用户注销就不能打开主页！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；要求：在过滤中实现！
HttpServletRequest request1 = (HttpServletRequest) servletRequest;
HttpServletResponse response1 = (HttpServletResponse) servletResponse;if (request1.getSession ().getAttribute (Constant.USER_SESSIN)==null) {response1.sendRedirect ("error.jsp");
}filterChain.doFilter (servletRequest,servletResponse); //过滤器往下走