一、实现的具体功能

(1)实现用户在线数量的统计，并显示在页面上。

(2)实现强制用户下线的功能。创建一个超链接，用于实现强制用户下线的功能。

(3)监听session的创建和销毁。

二、代码实现

(1)主页面：index.jsp。

pageEncoding="utf-8"%>

Insert title here

用户在线列表数量：${userTable.size()}

用户信息
${user.key }	踢你下线

(2)服务器监听器：SCListener.java文件。

package com.listener;

import java.util.Hashtable;

import javax.servlet.ServletContextEvent;

import javax.servlet.ServletContextListener;

import javax.servlet.annotation.WebListener;

import javax.servlet.http.HttpSession;

/**

* Application Lifecycle Listener implementation class SCListener

*

*/

@WebListener

public class SCListener implements ServletContextListener {

//在线用户数量sessionId , session

private static Hashtable userTable;

/**

* Default constructor.

*/

public SCListener() {

// TODO Auto-generated constructor stub

}

/**

* @see ServletContextListener#contextDestroyed(ServletContextEvent)

*/

public void contextDestroyed(ServletContextEvent arg0) {

// TODO Auto-generated method stub

//服务器关闭了

System.out.println("服务器关闭了......");

}

/**

* @see ServletContextListener#contextInitialized(ServletContextEvent)

*/

public void contextInitialized(ServletContextEvent sre) {

// TODO Auto-generated method stub

//服务器启动

System.out.println("服务器启动了......");

//创建用户在线列表

userTable = new Hashtable();

//放入全局对象,第一个userTable的Key

sre.getServletContext().setAttribute("userTable",userTable );

}

}

(3)UserListener.java文件。

package com.listener;

import java.util.Hashtable;

import javax.servlet.ServletContext;

import javax.servlet.annotation.WebListener;

import javax.servlet.http.HttpSession;

import javax.servlet.http.HttpSessionEvent;

import javax.servlet.http.HttpSessionListener;

/**

* Application Lifecycle Listener implementation class UserListener

*

*/

@WebListener

public class UserListener implements HttpSessionListener {

/**

* Default constructor.

*/

public UserListener() {

// TODO Auto-generated constructor stub

}

/**

* @see HttpSessionListener#sessionCreated(HttpSessionEvent)

*/

public void sessionCreated(HttpSessionEvent se) {

// TODO Auto-generated method stub

System.out.println("session创建了");

//获取全局对象

ServletContext sc = se.getSession().getServletContext();

//获取用户列表

Hashtable userTable = (Hashtable)sc.getAttribute("userTable");

//获取sessionId

String sid = se.getSession().getId();

//用户session信息添加到用户列表

userTable.put(sid, se.getSession());

System.out.println("用户在线数量："+userTable.size());

}

/**

* @see HttpSessionListener#sessionDestroyed(HttpSessionEvent)

*/

public void sessionDestroyed(HttpSessionEvent se) {

// TODO Auto-generated method stub

System.out.println("session销毁了");

ServletContext sc = se.getSession().getServletContext();

//获取用户列表

Hashtable userTable = (Hashtable)sc.getAttribute("userTable");

//获取sessionId

String sid = se.getSession().getId();

//移除用户列表中的用户

userTable.remove(sid);

}

}

(4)交互层用于实现强制用户下线的功能：KickUser.java文件。

package com.servlet;

import java.io.IOException;

import java.util.Hashtable;

import javax.servlet.ServletContext;

import javax.servlet.ServletException;

import javax.servlet.annotation.WebServlet;

import javax.servlet.http.HttpServlet;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

import javax.servlet.http.HttpSession;

/**

* Servlet implementation class KickUser

*/

@WebServlet("/KickUser")

public class KickUser extends HttpServlet {

private static final long serialVersionUID = 1L;

/**

* @see HttpServlet#HttpServlet()

*/

public KickUser() {

super();

// TODO Auto-generated constructor stub

}

/**

* @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)

*/

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

// TODO Auto-generated method stub

//获取Id

String sid = request.getParameter("sid");

//获取全局对象

ServletContext sc= request.getServletContext();

//获取用户列表

Hashtable userTable = (Hashtable)sc.getAttribute("userTable");

if(userTable.get(sid) != null) {

//销毁session

userTable.get(sid).invalidate();

}

response.sendRedirect("index.jsp");

}

/**

* @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)

*/

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

// TODO Auto-generated method stub

doGet(request, response);

}

}

三、运行结果

(1)用不同的浏览器打开，用户在线数就会增加，然后进行测试。

一只小小的蚂蚁

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标签：web,java,用户,userTable,Hashtable,import,servlet,javax

来源： https://blog.csdn.net/qq_44863179/article/details/104483179