通过session统计当前在线人数

<!-- 监听器配置 -->
	<listener>
		<listener-class>com.oracle.com.MyListener</listener-class>
	</listener>

　　配置

package com.oracle.com;

import javax.servlet.ServletContext;
import javax.servlet.http.HttpSession;
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;

public class MyListener implements HttpSessionListener {

	@Override
	public void sessionCreated(HttpSessionEvent event) {
		// System.out.println("创建了");
		HttpSession session = event.getSession();// 获得Session对象
		// 通过Session获得servletcontext对象
		ServletContext servletContext = session.getServletContext();
		/**
		 * 1.获取num值 
		 * 2.加1 
		 * 3.存入servletcontext
		 */
		Object object = servletContext.getAttribute("num");
		if (object == null) {
			servletContext.setAttribute("num", 1);
		} else {
			Object num = servletContext.getAttribute("num");
			int num1 = (int) num;
			servletContext.setAttribute("num", num1 + 1);
		}
	}

	@Override
	public void sessionDestroyed(HttpSessionEvent event) {
		// System.out.println("销毁了");
		HttpSession session = event.getSession();// 获得Session对象
		// 通过Session获得servletcontext对象
		ServletContext servletContext = session.getServletContext();
		/**
		 *	1.获取num值
		 *  2.减1 
		 *  3.存入servletcontext
		 */
		servletContext.setAttribute("num", (long) servletContext.getAttribute("num") - 1);
	}

}

　　统计

package com.oracle.com;

import java.io.IOException;
import java.io.PrintWriter;

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

public class servletDemo5 extends HttpServlet {
	@Override
	protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
		doPost(req, resp);
	}

	@Override
	protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

		req.setCharacterEncoding("utf-8");
		resp.setContentType("text/html;charset=utf-8");
		HttpSession session = req.getSession();// 创建Session
		// session.setMaxInactiveInterval(10);//设置失效时间10秒 不是销毁
		PrintWriter writer = resp.getWriter();
		ServletContext servletContext = getServletContext();
		Object num = servletContext.getAttribute("num");
		writer.write("在线人数:" + num);
	}
}