public class CharacterEncodingFilteer implements Filter {
    //初始化:在web服务器启动的时候就已经初始化完成了
    public void init(FilterConfig filterConfig) throws ServletException {
        System.out.println("CharacterEncodingFilter已经初始化");
    }
//chain
    /*
    1.过滤器中的代码，在过滤特定需求的请求中都会执行
    2.必须要让过滤器往下进行：filterChain.doFilter
     */
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        servletRequest.setCharacterEncoding("utf-8");
        servletResponse.setCharacterEncoding("utf-8");
        servletResponse.setContentType("text/html;charset=UTF-8");
        System.out.println("CharacterEncodingFilter执行前");
        filterChain.doFilter(servletRequest,servletResponse);//让我们的请求继续向下交接；没有这句话就会停在这个过滤器内
        System.out.println("CharacterEncodingFilter执行后");
    }
//销毁：在web服务器关闭的时候过滤器就会自动关闭
    public void destroy() {
        System.out.println("CharacterEncodingFilter已经销毁");
    }
}

//统计在线人数：统计session
public class OnlineCountLinster implements HttpSessionListener {
    //创建session的监听
    //一旦创建一个session就会触发一次这个事件
    public void sessionCreated(HttpSessionEvent se) {
        ServletContext ctx = se.getSession().getServletContext();
        System.out.println(se.getSession().getId());
        Integer onlineCount =(Integer) ctx.getAttribute("onlineCount");
        if(onlineCount==null){
            onlineCount=new Integer(1);
        }else {
            int count=onlineCount.intValue();
            onlineCount = new Integer(count + 1);
        }
        ctx.setAttribute("onlineCount",onlineCount);
    }
//销毁session的监听
    //一旦销毁session就会触发一次这个事件
    public void sessionDestroyed(HttpSessionEvent se) {
        ServletContext ctx = se.getSession().getServletContext();
        System.out.println(se.getSession().getId());
        se.getSession().invalidate();
        Integer onlineCount =(Integer) ctx.getAttribute("onlineCount");
        if(onlineCount==null){
            onlineCount=new Integer(0);
        }else {
            int count=onlineCount.intValue();
            onlineCount = new Integer(count -1);
        }
        ctx.setAttribute("onlineCount",onlineCount);
    }
}

public class TestPanel  {
    public static void main(String[] args) {
        Frame frame = new Frame("监听器GUI测试");//新建一个窗体
        Panel panel = new Panel(null);//面板
        frame.setLayout(null);//设置窗体布局
        frame.setBounds(300,300,500,500);//设置窗体位置，及显示大小
        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));
        frame.add(panel);
        frame.setVisible(true);//设置窗体可视化
        //监听事件，关闭监听事件
        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");
            }
        });

    }
}