java监视器统计在线人数

创建数据库连接

import java.sql.Connection;
import java.sql.DriverManager;

public class JDBC {
	public static final String DRIVER = "mysql.jdbc.Driver";//数据库驱动
	public static final String URL = "jdbc:mysql://127.0.0.1:3306/test?useUnicode=true&characterEncoding=UTF-8";//数据库路径，找到对应的数据库
	public static final String DBNAME = "root";
	public static final String PASSWORD = "zhangsan";
	public static Connection getConn() throws Exception{
		Class.forName(DRIVER);
		Connection conn = DriverManager.getConnection(URL, DBNAME, PASSWORD);
		return conn;
	}
}

创建实体类User

package com.User;

import java.io.Serializable;//接口的类是可序列化的

public class User implements Serializable{  //序列化功能的接口
	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 User(int id, String username, String password) {
		super();
		this.id = id;
		this.username = username;
		this.password = password;
	}
	public User(String username, String password) {
		this.username = username;
		this.password = password;
	}
	public User() {
		super();
		// TODO Auto-generated constructor stub
	}
	
}

UserDao.class 使用登录方法

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

import com.DBUtil.JDBC;

public class UserDao {
	public User login(String username, String password) {
		User user=null;
		Connection conn = null;
		PreparedStatement pstate = null;
		ResultSet res = null;
		try {
			conn=JDBC.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 User(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;
	}

}

监视器Listener

import java.util.ArrayList;
import java.util.List;

import javax.servlet.ServletContext;
import javax.servlet.ServletContextAttributeEvent;
import javax.servlet.ServletContextAttributeListener;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
import javax.servlet.annotation.WebListener;

/**
 * Application Lifecycle Listener implementation class Listener
 *
 */
@WebListener
public class Listener implements ServletContextListener, ServletContextAttributeListener {
      
	ServletContext application = null;

    public Listener() {
        // TODO Auto-generated constructor stub
    }

    public void contextInitialized(ServletContextEvent sce)  { 
    	List<String> list = new ArrayList<String>();
		//用来保存所有已登录的用户
		application =  sce.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(ServletContextAttributeEvent scae)  { 
    	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)scae.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(ServletContextAttributeEvent scae)  { 
    	List<String> list = (List<String>)application.getAttribute("allUser");
		list.remove((String)scae.getValue());
		application.setAttribute("allUser", list);
    }	
    public void contextDestroyed(ServletContextEvent sce)  { 
    	System.out.println("服务器关闭");
    }
    public void attributeReplaced(ServletContextAttributeEvent scae)  { 
         // TODO Auto-generated method stub
    }	
}

servlet

import java.io.IOException;
import java.util.List;

import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

import com.User.UserDao;
import com.User.User;

/**
 * Servlet implementation class UserServlet
 */
@WebServlet("/Login")

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){
			User 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);
	}
 
}

xml配置

<listener>
    <listener-class>com.Listener.Listener</listener-class>
  </listener>

登录页login,jsp

<%@page contentType="text/html; charset=utf-8"%>
<%@page import="java.util.*" %>
<%
	String path  = request.getContextPath();
 %>
 
<html>
	<body>
	
		<form action="<%=path %>/Login" method="get">
			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>

主页面 index.jsp 统计登录人数

<%@ 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">注销</a>
  </body>
</html>

注销页

<%@ 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>