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:
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< listener >
< listener-class >net.jvsun.ListenerTest</ listener-class >
</ listener >
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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:
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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;
}
}
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用户实体类:
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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
}
}
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数据库处理类:
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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;
}
}
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servlet类:
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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);
}
}
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监听类:
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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) {
}
}
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登录页面
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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">
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 >
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显示在线人数和在线人员的列表界面
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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 >
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注销界面:
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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 >
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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