JavaWeb的监听器和过滤器你了解吗

public class ContextListener1 implements ServletContextListener {
    @Override
    public void contextInitialized(ServletContextEvent servletContextEvent) {
        System.out.println("init");
        //创建map集合
        Map<String, Integer> map = new HashMap<String, Integer>();
        //    获取全局对象
        ServletContext context = servletContextEvent.getServletContext();
        context.setAttribute("map", map);
        System.out.println(map.isEmpty());
        System.out.println(map);
    }
    @Override
    public void contextDestroyed(ServletContextEvent servletContextEvent) {
        System.out.println("destory");
    }
}

<%
    //获取用户ip地址
    String ServerName = request.getServerName();
    //获取全局对象
    Map<String, Integer> map = (Map<String, Integer>) application.getAttribute("map");
    if (map.containsKey(ServerName)) {
        map.put(ServerName, map.get(ServerName) + 1);
    } else {
        map.put(ServerName, 1);
    }
    int count = map.get(ServerName);
    int size = map.size();
%>
<h4>ip地址是:<%=ServerName%>,您是第<%=count%>位访问的用户,当前服务器共被<%=size%>个用户访问过</h4>

package listener;
import javax.servlet.*;
import javax.servlet.Http.httpsessionAttributeListener;
import javax.servlet.http.HttpSessionBindingEvent;

public class AttrListener implements ServletContextAttributeListener, ServletRequestAttributeListener, HttpSessionAttributeListener {
    @Override
    public void attributeAdded(ServletContextAttributeEvent servletContextAttributeEvent) {
    //    向全局作用域中添加值的监听器
    }
    @Override
    public void attributeRemoved(ServletContextAttributeEvent servletContextAttributeEvent) {
    //    向全局作用域删除值的监听器
    }
    @Override
    public void attributeReplaced(ServletContextAttributeEvent servletContextAttributeEvent) {
    //    向全局域对象修改值的监听器
    }
    @Override
    public void attributeAdded(ServletRequestAttributeEvent servletRequestAttributeEvent) {
    //    向request域中添加值的监听器
    }
    @Override
    public void attributeRemoved(ServletRequestAttributeEvent servletRequestAttributeEvent) {
    //    向request域中删除值的监听器
    }
    @Override
    public void attributeReplaced(ServletRequestAttributeEvent servletRequestAttributeEvent) {
    //    向request域中修改值的监听器
    }
    @Override
    public void attributeAdded(HttpSessionBindingEvent httpSessionBindingEvent) {
    //    向session域中添加值的监听器
    }
    @Override
    public void attributeRemoved(HttpSessionBindingEvent httpSessionBindingEvent) {
    //    向session域中删除值的监听器
    }
    @Override
    public void attributeReplaced(HttpSessionBindingEvent httpSessionBindingEvent) {
    //    向session域中修改值的监听器
    }
}

1.编写java	类实现Filter接口
2.重写doFilter()方法
3.设置拦截的url