本文實例為大家分享了servlet統計在線人數的具體代碼，供大家參考，具體內容如下
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：
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<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：
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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：
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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：
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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：
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public class UserServlet extends HttpServlet{ @Override protected 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"); } @Override protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { doGet(req, resp); } } |
監聽類：
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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
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<%@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
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<%@ 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%>" rel="external nofollow" rel="external nofollow" > <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" rel="external nofollow" >注銷</a> </body> </html> |
注銷界面：
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<%@ 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%>" rel="external nofollow" rel="external nofollow" > <title>logout</title> </head> <body> <% session.removeAttribute("username"); session.invalidate(); response.sendRedirect("login.jsp"); %> </body> </html> |
代碼下載地址：servlet統計在線人數
以上就是本文的全部內容，希望對大家的學習有所幫助，也希望大家多多支持服務器之家。
原文鏈接：http://blog.csdn.net/weixin_36380516/article/details/70144559
