ServletContext事件監聽器---->針對applicationScope

?ServletContextListener(*)

對整個Web應用的裝載和卸載進行監聽。

?ServletContextAttributeListener

對ServletContext中的信息存放、刪除和替換進行監聽。

ServletContext就是Servlet上下文監聽，在web中表示的是對啟動服務和銷毀服務進行監聽，需要實現的接口：

ServletContextListener接口，實現的就是對上下午進行監聽：

void contextInitialized(ServletContextEvent sce)：啟動上下文時的監聽

void contextDestroyed(ServletContextEvent sce)：銷毀上下文時進行的監聽

除了對上下文的啟動和銷毀進行監聽的之外，還可以對上下文的屬性進行監聽：ServletContextAttributeListener接口。

void attributeAdded(ServletContextAttributeEvent event)：設置上下文屬性監聽

void attributeRemoved(ServletContextAttributeEvent event)：移除上下文屬性的監聽

void attributeReplaced(ServletContextAttributeEvent event)：修改上下文屬性的監聽

ServletContextAttributeEvent：事件，可以通過事件取得屬性的內容和名稱。

·取得屬性名稱：public java.lang.String getName()

·取得屬性的值：public java.lang.Object getValue()

效果如下圖：

當登錄一個賬號時

打開另一個瀏覽器，再登錄一個賬號

如上圖，我們可以看到，程序已經完成了統計在線人數和顯示人員列表的功能，那么他的實現流程是什么呢？

我們可以通過ServletContextListener完成在線人數的統計和顯示在線人數列表，首先listener和filter一樣要在web.xml中進行描述。

代碼如下：

<listener> <listener-class>net.jvsun.ListenerTest</listener-class> </listener>

為了測試這個程序，我們也必須完成用戶登錄功能。

數據庫連接幫助類：

public class JDBCHelper {public static final String DRIVER = "oracle.jdbc.driver.OracleDriver";public static final String URL = "jdbc:oracle:thin:@localhost:1521:xxx";public static final String DBNAME = "scott";public static final String PASSWORD = "xxx";public static Connection getConn() throws Exception{Class.forName(DRIVER);Connection conn = DriverManager.getConnection(URL, DBNAME, PASSWORD);return conn;} }用戶實體類：

public class UserPOJO implements Serializable{private static final long serialVersionUID = 7554548269035753256L;private int id;private String username;private String password;public int getId() {return id;}public void setId(int id) {this.id = id;}public String getUsername() {return username;}public void setUsername(String username) {this.username = username;}public String getPassword() {return password;}public void setPassword(String password) {this.password = password;}public UserPOJO(int id, String username, String password) {super();this.id = id;this.username = username;this.password = password;}public UserPOJO(String username, String password) {this.username = username;this.password = password;}public UserPOJO() {super();// TODO Auto-generated constructor stub}}
數據庫處理類：

public class UserDAO {public UserPOJO login(String username, String password) {UserPOJO user=null;Connection conn = null;PreparedStatement pstate = null;ResultSet res = null;try {conn=JDBCHelper.getConn();String sql="select id,username from userinfo where username=? and password=?";pstate = conn.prepareStatement(sql);pstate.setString(1, username);pstate.setString(2, password);res = pstate.executeQuery();while(res.next()){user=new UserPOJO(res.getInt(1),username,null);}} catch (Exception e) {e.printStackTrace();}finally{try {res.close();pstate.close();conn.close();} catch (SQLException e) {e.printStackTrace();}}return user;} }

servlet類：

public class UserServlet extends HttpServlet{@Overrideprotected void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {String path = request.getContextPath();response.setContentType("text/html; charset=utf-8");request.setCharacterEncoding("utf-8");String username = request.getParameter("username");String password = request.getParameter("password");ServletContext application = this.getServletContext();//取得application對象List<String> list = (List<String>) application.getAttribute("allUser");if(list.indexOf(username) == -1){UserPOJO pojo = new UserDAO().login(username, password);if(null != pojo){HttpSession session = request.getSession(true);//取得session對象session.setAttribute("userName", username);}}response.sendRedirect(path+"/index.jsp");}@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp)throws ServletException, IOException {doGet(req, resp);}}

監聽類：

public class ListenerTest implements ServletContextListener,HttpSessionAttributeListener,HttpSessionListener{ServletContext application = null;public void contextDestroyed(ServletContextEvent event) {System.out.println("服務器關閉");}public void contextInitialized(ServletContextEvent event) {List<String> list = new ArrayList<String>();//用來保存所有已登錄的用戶application = event.getServletContext();//取得application對象application.setAttribute("allUser", list);//將集合設置到application范圍屬性中去}public void attributeAdded(HttpSessionBindingEvent se) {List<String> list = (List<String>)application.getAttribute("allUser");//假設：用戶登陸成功之后，只將戶名設置到session中String userName = (String)se.getValue();//取得用戶名if(list.indexOf(userName) == -1){//表示此用戶之前沒有登陸list.add(userName);application.setAttribute("allUser", list);}}public void attributeRemoved(HttpSessionBindingEvent se) {List<String> list = (List<String>)application.getAttribute("allUser");list.remove((String)se.getValue());application.setAttribute("allUser", list);}public void attributeReplaced(HttpSessionBindingEvent se) {}public void sessionCreated(HttpSessionEvent event) {}public void sessionDestroyed(HttpSessionEvent event) {} }

登錄頁面

<%@page contentType="text/html; charset=utf-8"%> <%@page import="java.util.*" %> <%String path = request.getContextPath();%><html><body><form action="<%=path %>/Login" method="post">賬號：<input type="text" name="username" /><br />密碼：<input type="password" name="password" /><br /><input type="submit" value="提交" /></form></body></html>
顯示在線人數和在線人員的列表界面

<%@ 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></title></head><body><ul><%System.out.println(application.getAttribute("allUser"));if(null != application.getAttribute("allUser")){List<String> list = (List<String>)application.getAttribute("allUser");%><h2>在線人數:<%=list.size() %></h2><%for(String s:list){%><a>姓名：</a><%=s %><a>---->此時在線</a><br><%}}%></ul><hr/><a href="<%=path %>/logout.jsp">注銷</a></body> </html>
注銷界面：

<%@ 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>logout</title></head><body><%session.removeAttribute("username");session.invalidate();response.sendRedirect("login.jsp");%></body> </html>
代碼下載地址：http://download.csdn.net/detail/weixin_36380516/9811993

總結

以上是生活随笔為你收集整理的servlet监听完成统计在线人数，显示在线人员列表(附源码)的全部內容，希望文章能夠幫你解決所遇到的問題。

如果覺得生活随笔網站內容還不錯，歡迎將生活随笔推薦給好友。