本文实例为大家分享了servlet统计在线人数的具体代码，供大家参考，具体内容如下
ServletContext事件监听器---->针对applicationScope
ServletContextListener(*)
对整个Web应用的装载和卸载进行监听。
ServletContextAttributeListener
对ServletContext中的信息存放、删除和替换进行监听。
ServletContext就是Servlet上下文监听，在web中表示的是对启动服务和销毁服务进行监听，需要实现的接口：
ServletContextListener接口，实现的就是对上下午进行监听：
void contextInitialized(ServletContextEvent sce)：启动上下文时的监听
void contextDestroyed(ServletContextEvent sce)：销毁上下文时进行的监听
除了对上下文的启动和销毁进行监听的之外，还可以对上下文的属性进行监听：ServletContextAttributeListener接口。
void attributeAdded(ServletContextAttributeEvent event)：设置上下文属性监听
void attributeRemoved(ServletContextAttributeEvent event)：移除上下文属性的监听
void attributeReplaced(ServletContextAttributeEvent event)：修改上下文属性的监听
ServletContextAttributeEvent：事件，可以通过事件取得属性的内容和名称。
·取得属性名称：public java.lang.String getName()
·取得属性的值：public java.lang.Object getValue()
效果如下图：
当登录一个账号时
打开另一个浏览器，再登录一个账号
如上图，我们可以看到，程序已经完成了统计在线人数和显示人员列表的功能，那么他的实现流程是什么呢？
我们可以通过ServletContextListener完成在线人数的统计和显示在线人数列表，首先listener和filter一样要在web.xml中进行描述。
代码如下：
|
1
2
3
|
<listener> <listener-class>net.jvsun.ListenerTest</listener-class> </listener> |
为了测试这个程序，我们也必须完成用户登录功能。
数据库连接帮助类：
|
1
2
3
4
5
6
7
8
9
10
11
|
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; } } |
用户实体类：
|
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
|
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 } } |
数据库处理类：
|
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
|
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类：
|
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
|
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对象 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对象 session.setAttribute("userName", username); } } response.sendRedirect(path+"/index.jsp"); } @Override protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { doGet(req, resp); } } |
监听类：
|
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
|
public class ListenerTest implements ServletContextListener,HttpSessionAttributeListener,HttpSessionListener{ ServletContext application = null; public void contextDestroyed(ServletContextEvent event) { System.out.println("服务器关闭"); } public void contextInitialized(ServletContextEvent event) { List<String> list = new ArrayList<String>(); //用来保存所有已登录的用户 application = event.getServletContext(); //取得application对象 application.setAttribute("allUser", list); //将集合设置到application范围属性中去 } public void attributeAdded(HttpSessionBindingEvent se) { List<String> list = (List<String>)application.getAttribute("allUser"); //假设：用户登陆成功之后，只将户名设置到session中 String userName = (String)se.getValue(); //取得用户名 if(list.indexOf(userName) == -1){ //表示此用户之前没有登陆 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) { } } |
登录页面
|
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
|
<%@page contentType="text/html; charset=utf-8"%> <%@page import="java.util.*" %> <% String path = request.getContextPath(); %> <html> <body> <form action="<%=path %>/Login" method="post"> 账号： <input type="text" name="username" /> <br /> 密码： <input type="password" name="password" /> <br /> <input type="submit" value="提交" /> </form> </body> </html> |
显示在线人数和在线人员的列表界面
|
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
|
<%@ 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>在线人数:<%=list.size() %></h2> <% for(String s:list){ %> <a>姓名：</a><%=s %><a>---->此时在线</a><br> <% } } %> </ul> <hr/> <a href="<%=path %>/logout.jsp" rel="external nofollow" >注销</a> </body> </html> |
注销界面：
|
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
|
<%@ 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> |
代码下载地址：servlet统计在线人数
以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持服务器之家。
原文链接：http://blog.csdn.net/weixin_36380516/article/details/70144559
