共计 3170 个字符，预计需要花费 8 分钟才能阅读完成。
实现思路
常见的流程是, 标准的 mvc 即 登录表单, 用户提交数据到登录检查, 若登录检查通过以后, 触发 session 事件, 保存进入在线人员列表中, 页面跳转到在线用户列表, 若用户注销, 从在线列表中删除.
代码如下
使用 set 集合, 即 set 集合去重 原因 内部存储为 map,mqp 的键值对为 hashcode 由于哈希表的特征 即 set 可去重
项目结构
创建迭代器
package com.ming.listener;
import javax.servlet.ServletContext;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
import javax.servlet.http.HttpSessionAttributeListener;
import javax.servlet.http.HttpSessionBindingEvent;
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;
import java.util.Set;
import java.util.TreeSet;
// 对 servlet 上下文监听
public class OnlineUserList implements HttpSessionAttributeListener, HttpSessionListener, ServletContextListener {
private ServletContext servletContext = null;
// 增加 session 属性的时候, 触发事件
// session 属性增加
@Override
public void attributeAdded(HttpSessionBindingEvent httpSessionBindingEvent) {
Set all = (Set)this.servletContext.getAttribute(“online”);
all.add(httpSessionBindingEvent.getValue());
this.servletContext.setAttribute(“online”, all);
}
// 用户注销登录
// session 属性删除
@Override
public void attributeRemoved(HttpSessionBindingEvent httpSessionBindingEvent) {
Set all = (Set)this.servletContext.getAttribute(“online”);
all.remove(httpSessionBindingEvent.getValue());
this.servletContext.setAttribute(“online”, all);
}
@Override
public void attributeReplaced(HttpSessionBindingEvent httpSessionBindingEvent) {
}
// 上下文初始化
// 初始化
@Override
public void contextInitialized(ServletContextEvent servletContextEvent) {
// 获得上下文实栗
this.servletContext = servletContextEvent.getServletContext();
// 设置保存 set 集合
this.servletContext.setAttribute(“online”, new TreeSet());
}
@Override
public void contextDestroyed(ServletContextEvent servletContextEvent) {
}
@Override
public void sessionCreated(HttpSessionEvent httpSessionEvent) {
}
// session 销毁
@Override
public void sessionDestroyed(HttpSessionEvent httpSessionEvent) {
Set all = (Set)this.servletContext.getAttribute(“online”);
all.remove(httpSessionEvent.getSession().getAttribute(“id”));
this.servletContext.setAttribute(“online”, all);
}
}
配置文件
<!DOCTYPE web-app PUBLIC
“-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN”
“http://java.sun.com/dtd/web-app_2_3.dtd” >
<web-app>
<display-name>Archetype Created Web Application</display-name>
<listener>
<listener-class>com.ming.listener.OnlineUserList</listener-class>
</listener>
<filter>
<filter-name>LoginFile</filter-name>
<filter-class>com.ming.filter.LoginFile</filter-class>
</filter>
<filter-mapping>
<filter-name>LoginFile</filter-name>
<url-pattern>/index.jsp</url-pattern>
</filter-mapping>
<servlet>
<servlet-name>login</servlet-name>
<servlet-class>com.ming.servlrt.LoginServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>login</servlet-name>
<url-pattern>/loginServlet</url-pattern>
</servlet-mapping>
</web-app>
在线用户统计
<%@ page import=”java.util.Set” %>
<%@ page import=”java.util.Iterator” %>
<%@ page import=”javax.swing.text.html.HTMLDocument” %><%–
Created by IntelliJ IDEA.
User: ming
Date: 19-3-17
Time: 上午 4:14
To change this template use File | Settings | File Templates.
–%>
<%@ page contentType=”text/html;charset=UTF-8″ language=”java” %>
<html>
<head>
<title>Title</title>
</head>
<body>
您已经登录
显示用户在线
<%
Set all = (Set)super.getServletContext().getAttribute(“online”);
Iterator iterator = all.iterator();
while(iterator.hasNext()){
%>
<%=iterator.next()%>
<%
}
%>
</body>
</html>
运行效果