java session HttpSessionListener、HttpSessionBindingListener使用区别，实现在线人数统计以及踢出用户...

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java web项目中管理session的时候，除了在web.xml文件中设置过时时间

<session-config><session-timeout>2</session-timeout>
</session-config>

xxx分钟，还可以通过 HttpSessionListener 接口或HttpSessionBindingListener接口来实现对session的监控，通过监听session的新建和销毁来控制

实现HttpSessionListener接口：

package listener;import java.util.List;
import javax.servlet.ServletContext;
import javax.servlet.http.HttpSession;
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;public class OnlineListener implements HttpSessionListener {public void sessionCreated(HttpSessionEvent event) {System.out.println("新建session:" + event.getSession().getId());}public void sessionDestroyed(HttpSessionEvent event) {HttpSession session = event.getSession();ServletContext application = session.getServletContext();// 取得登录的用户名String username = (String) session.getAttribute("username");// 从在线列表中删除用户名List onlineUserList = (List) application.getAttribute("onlineUserList");onlineUserList.remove(username);System.out.println(username+"已经退出！");}
}

后要在web.xml中配置监听接口配置：

<listener><listener-class>listener.OnlineListener</listener-class>
</listener>

当用户首次访问网站页面的时候，框架就会生成一个sessionID这时执行listener.OnlineListener.sessionCreated()方法，执行操作，不是对单个session与用户的是对整个全局的session的操作

项目其他文件代码：
index.jsp

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html><head><base href="<%=basePath%>"><title>My JSP 'index.jsp' starting page</title><meta http-equiv="pragma" content="no-cache"><meta http-equiv="cache-control" content="no-cache"><meta http-equiv="expires" content="0">    <meta http-equiv="keywords" content="keyword1,keyword2,keyword3"><meta http-equiv="description" content="This is my page"></head><body><form action="httpSessionLogin.jsp" method="get">HttpSessionListener方式监听Session：<br/>登陆：<input id="username" name="username"/><input type="submit"/></form></body>
</html>

httpSessionLogin.jsp:

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%@page import="listener.OnlineListener"%>
<%request.setCharacterEncoding("UTF-8");// 取得登录的用户名String username = request.getParameter("username");// 把用户名保存进sessionSystem.out.println("jspsession:" + session.getId());session.setAttribute("username", username);session.setAttribute("onlineUserList", new OnlineListener(username));System.out.println("用户："+username+" 登陆成功");// 把用户名放入在线列表List onlineUserList = (List) application.getAttribute("onlineUserList");// 第一次使用前，需要初始化if (onlineUserList == null) {onlineUserList = new ArrayList();application.setAttribute("onlineUserList", onlineUserList);}onlineUserList.add(username);// 成功response.sendRedirect("result.jsp");
%>

result.jsp

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html><head><base href="<%=basePath%>"><title>My JSP 'index.jsp' starting page</title><meta http-equiv="pragma" content="no-cache"><meta http-equiv="cache-control" content="no-cache"><meta http-equiv="expires" content="0">    <meta http-equiv="keywords" content="keyword1,keyword2,keyword3"><meta http-equiv="description" content="This is my page"></head><body>登陆成功<h3>您好：${username} [<a href="logout.jsp">注销</a>]</h3>当前在线用户：<table><%List onlineUserList = (List) application.getAttribute("onlineUserList");for (int i = 0; i < onlineUserList.size(); i++) {String onlineUsername = (String) onlineUserList.get(i);%><tr><td><%=onlineUsername%></td><td><a href="deleteUser.jsp?username=<%=onlineUsername%>">删除</a></td></tr><%}%></table></body>
</html>

而HttpSessionBindingListener运用时不用在web.xml中配置，HttpSessionBindingListener虽然叫做监听器，但使用方法与HttpSessionListener完全不同。我们实际看一下它是如何使用的。新建类OnlineUserBindingListener，实现HttpSessionBindingListener接口，构造方法传入username参数，HttpSessionBindingListener内有两个方法valueBound(HttpSessionBindingEvent event)和valueUnbound(HttpSessionBindingEvent event)，前者为数据绑定，后者为取消绑定所谓对session进行数据绑定，就是调用session.setAttribute()把HttpSessionBindingListener保存进session中

index.jsp

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html><head><base href="<%=basePath%>"><title>My JSP 'index.jsp' starting page</title><meta http-equiv="pragma" content="no-cache"><meta http-equiv="cache-control" content="no-cache"><meta http-equiv="expires" content="0">    <meta http-equiv="keywords" content="keyword1,keyword2,keyword3"><meta http-equiv="description" content="This is my page"></head><body><form action="sessionBindingLogin.jsp" method="get">HttpSessionBindingListener方式监听Session：<br/>登陆：<input id="username" name="username"/><input type="submit"/></form></body>
</html>

sessionBindingLogin.jsp:

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%@page import="listener.OnlineBindingListener"%>
<%request.setCharacterEncoding("UTF-8");// 取得登录的用户名String username = request.getParameter("username");// 把用户名放入在线列表session.setAttribute("onlineUserBindingListener", new OnlineBindingListener(username));// 成功response.sendRedirect("result.jsp");
%>

package listener;import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;import javax.servlet.ServletContext;
import javax.servlet.http.HttpSession;
import javax.servlet.http.HttpSessionBindingEvent;
import javax.servlet.http.HttpSessionBindingListener;public class OnlineBindingListener implements HttpSessionBindingListener {String username;public OnlineBindingListener(String username){this.username=username;}public void valueBound(HttpSessionBindingEvent event) {HttpSession session = event.getSession();System.out.println("创建Session:"+session.getId());System.out.println("username:"+username);session.setAttribute("username", username);ServletContext application = session.getServletContext();// 把用户名放入在线列表List onlineUserList = (List) application.getAttribute("onlineUserList");Map<String, HttpSession> sessionMap = (Map<String, HttpSession>)application.getAttribute("sessionMap");// 第一次使用前，需要初始化if (onlineUserList == null) {onlineUserList = new ArrayList();application.setAttribute("onlineUserList", onlineUserList);}if (sessionMap == null) {sessionMap = new HashMap<String, HttpSession>();application.setAttribute("sessionMap", sessionMap);}onlineUserList.add(this.username);sessionMap.put(username, session);}public void valueUnbound(HttpSessionBindingEvent event) {HttpSession session = event.getSession();ServletContext application = session.getServletContext();// 从在线列表中删除用户名List onlineUserList = (List) application.getAttribute("onlineUserList");onlineUserList.remove(this.username);System.out.println("Session实效:"+session.getId());System.out.println(this.username + "退出。");}}

把某人踢出登陆状态：

deleteUser.jsp

<%@ page language="java" import="java.util.*,javax.servlet.*" pageEncoding="UTF-8"%>
<%request.setCharacterEncoding("UTF-8");// 取得登录的用户名String username = request.getParameter("username");System.out.println(username);Map<String, HttpSession> sessionMap = (Map<String, HttpSession>)application.getAttribute("sessionMap");HttpSession otherSession = (HttpSession)sessionMap.get(username);//otherSession.removeAttribute("username");otherSession.invalidate();sessionMap.remove(username);// 成功response.sendRedirect("result.jsp");
%>

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