Servlet、Filter、Listener执行的先后顺序

Listener在web容器中优先于Fiter执行，即在Filter之前执行
Fiter在web容器中优先于Servlet执行，即在Servlet之前执行
ServletContextListener最先执行，容器一启动便执行它的contextInitialized方法。
示例代码如下:

package com.anxiesoft.util;

import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;

import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
import javax.servlet.http.HttpSession;
import javax.servlet.http.HttpSessionBindingEvent;
import javax.servlet.http.HttpSessionBindingListener;
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;

public class MyListener implements HttpSessionListener, ServletContextListener,
  HttpSessionBindingListener {
 private static Map hUserName = new HashMap();

 @Override
 public void sessionCreated(HttpSessionEvent arg0) {
  System.out.println(".....sessionCreated.......");
 }

 @Override
 public void sessionDestroyed(HttpSessionEvent arg0) {
  System.out.println(".....sessionDestroyed.......");
  hUserName.remove(arg0.getSession().getId());
 }

 public static boolean isOnline(HttpSession session) {
  boolean flag = true;
  if (hUserName.containsKey(session.getId())) {
   flag = true;
  } else {
   flag = false;
  }
  return flag;
 }

 public static boolean isAlreadyEnter(HttpSession session, String sUserName) {
  boolean flag = false;
  if (hUserName.containsValue(sUserName)) {
   flag = true;
   // 遍历原来的hUserName，删除原用户对应的SessionId(即删除原来的sessionId和Username)
   Iterator iter = hUserName.entrySet().iterator();
   while (iter.hasNext()) {
    Map.Entry entry = (Map.Entry) iter.next();
    Object key = entry.getKey();
    Object value = entry.getValue();
    if (((String) value).equals(sUserName)) {
     hUserName.remove(key);
    }
   }
   hUserName.put(session.getId(), sUserName);
   System.out.println("hUserName = " + hUserName);
  } else {
   flag = false;
   hUserName.put(session.getId(), sUserName);
   System.out.println("hUserName = " + hUserName);
  }
  return flag;
 }

 @Override
 public void contextDestroyed(ServletContextEvent arg0) {
  System.out.println("......contextDestroyed..........");
 }

 @Override
 public void contextInitialized(ServletContextEvent arg0) {
  System.out.println("......contextInitialized..........");
 }

 @Override
 public void valueBound(HttpSessionBindingEvent arg0) {
  System.out.println("......valueBound..........");
 }

 @Override
 public void valueUnbound(HttpSessionBindingEvent arg0) {
  System.out.println("......valueUnbound..........");
 }
}