标签：
1)使用Servlet 3.0新标准jar包
2)JDK必须是1.6以上版本
3)编译器的编译级别为6.0
4)在web.xml文件中，使用3.0规范
5)使用支持Servlet 3.0特性的Web容器，比如Tomcat7
@WebListener
该注解用于将类声明为监听器，被@WebListener标注的类必须实现以下至少一个接口：ServletContextListener
ServletContextAttributeListener
ServletRequestListener
ServletRequestAttributeListener
HttpSessionListener
HttpSessionAttributeListener
Servlet3.0下无法确定监听器的启动顺序，和过滤器是一样的。
web.xml中的配置
<listener>
<listener-class>com.listeber.SimpleListener</listener-class>
</listener>
演变为：
@WebListener("This is only a demo listener")
实例代码
User.java源代码：
package com.domain;
public class User {
private String sessionIdString;
private String ipString;
private String firstTimeString;
public String getSessionIdString() {
return sessionIdString;
}
public void setSessionIdString(String sessionIdString) {
this.sessionIdString = sessionIdString;
}
public String getIpString() {
return ipString;
}
public void setIpString(String ipString) {
this.ipString = ipString;
}
public String getFirstTimeString() {
return firstTimeString;
}
public void setFirstTimeString(String firstTimeString) {
this.firstTimeString = firstTimeString;
}
}
SessionListener.java源代码：
package com.listener;
import java.util.ArrayList;
import javax.servlet.annotation.WebListener;
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;
import com.domain.User;
import com.utils.SessionUtil;
/**
* Application Lifecycle Listener implementation class SimpleListener
*
*/
@WebListener
public class SessionListener implements HttpSessionListener {
private int userNumber = 0;
/**
* Default constructor.
*/
public SessionListener() {
// TODO Auto-generated constructor stub
}
/**
* @see HttpSessionListener#sessionCreated(HttpSessionEvent)
*/
public void sessionCreated(HttpSessionEvent httpSessionEvent) {
userNumber++;
httpSessionEvent.getSession().getServletContext().setAttribute("userNumber", userNumber);
}
/**
* @see HttpSessionListener#sessionDestroyed(HttpSessionEvent)
*/
public void sessionDestroyed(HttpSessionEvent httpSessionEvent) {
userNumber--;
httpSessionEvent.getSession().getServletContext().setAttribute("userNumber", userNumber);
ArrayList<User> userList = null;
userList = (ArrayList<User>)httpSessionEvent.getSession().getServletContext().getAttribute("userList");
if(SessionUtil.getUserBySessionId(userList,httpSessionEvent.getSession().getId())!=null ){
userList.remove(SessionUtil.getUserBySessionId(userList, httpSessionEvent.getSession().getId()));
}
}
}
RequestListener.java源代码：
package com.listener;
import java.text.SimpleDateFormat;
import java.util.ArrayList;
import java.util.Date;
import javax.servlet.ServletRequestEvent;
import javax.servlet.ServletRequestListener;
import javax.servlet.annotation.WebListener;
import javax.servlet.http.HttpServletRequest;
import com.domain.User;
import com.utils.SessionUtil;
/**
* Application Lifecycle Listener implementation class RequestListener
*
*/
@WebListener
public class RequestListener implements ServletRequestListener {
private ArrayList<User> userList;//在线用户列表
/**
* Default constructor.
*/
public RequestListener() {
// TODO Auto-generated constructor stub
}
/**
* @see ServletRequestListener#requestDestroyed(ServletRequestEvent)
*/
public void requestDestroyed(ServletRequestEvent servletRequestEvent) {
}
/**
* @see ServletRequestListener#requestInitialized(ServletRequestEvent)
*/
public void requestInitialized(ServletRequestEvent servletRequestEvent) {
userList = (ArrayList<User>) servletRequestEvent.getServletContext().getAttribute("userList");
if(userList==null){
userList = new ArrayList<User>();
}
HttpServletRequest request = (HttpServletRequest) servletRequestEvent.getServletRequest();
String sessionIdString = request.getSession().getId();
if(SessionUtil.getUserBySessionId(userList,sessionIdString)==null){
User user = new User();
user.setSessionIdString(sessionIdString);
user.setFirstTimeString(new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").format(new Date()));
user.setIpString(request.getRemoteAddr());
userList.add(user);
}
servletRequestEvent.getServletContext().setAttribute("userList", userList);
}
}
SessionUtils.java源代码：
package com.utils;
import java.util.ArrayList;
import com.domain.User;
public class SessionUtil {
public static Object getUserBySessionId(ArrayList<User> userList,String sessionIdString) {
for (int i = 0; i < userList.size(); i++) {
User user = userList.get(i);
if(user.getSessionIdString().equals(sessionIdString)){
return user;
}
}
return null;
}
}
show.jsp页面：
<%@page import="com.domain.User"%>
<%@page import="java.util.ArrayList"%>
<%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>统计页面</title>
</head>
<body>
<h1>当前在线用户人数统计</h1>
<hr/>
当前在线用户人数：${userNumber}<br/>
<%
ArrayList<User> userList = (ArrayList<User>)request.getServletContext().getAttribute("userList");
if(userList!=null){
for(int i=0;i<userList.size();i++){
User user = userList.get(i);
%>
IP：<%=user.getIpString() %><br/>
FirstTime：<%=user.getFirstTimeString() %><br/>
SessionID：<%=user.getSessionIdString() %><br/>
<%
}
}
%>
</body>
</html>
运行结果：
对于过滤器和监听器的学习暂时告一段落，很推荐看的博文：
Java 过滤器：地址是：http://www.cnblogs.com/CBDoctor/p/4235082.html
Java 监听器：地址是：http://www.cnblogs.com/CBDoctor/p/4232859.html
javaweb学习总结(四十二)——Filter(过滤器)学习：地址是：http://www.cnblogs.com/xdp-
gacl/category/574705.html
javaweb学习总结(四十三)——Filter高级开发：地址是：http://www.cnblogs.com/xdp-
gacl/p/3948353.html
javaweb学习总结(四十四)——监听器(Listener)学习：地址是：http://www.cnblogs.com/xdp-
gacl/p/3961929.html
javaweb学习总结(四十五)——监听器(Listener)学习二：地址是：http://www.cnblogs.com/xdp-
gacl/p/3969249.html
javaweb学习总结(四十六)——Filter(过滤器)常见应用：地址是：http://www.cnblogs.com/xdp-
gacl/p/3948422.html
javaweb学习总结(四十七)——监听器(Listener)在开发中的应用：地址是：http://www.cnblogs.com/xdp-
gacl/p/3965508.html
大神的文章很受用，看的我直接爽翻了。
大牛的博客地址：http://www.cnblogs.com/xdp-gacl/
标签：
原文地址：http://blog.csdn.net/erlian1992/article/details/52220214
