Session使用（14）

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用session统计某个网页的访问人数（因为我还不会js，所以就做了个简易版本的）

1、创建Session监听器，每创建了一个Session对象就执行监听类中·的sessionCreated方法。

package com.ykh.session;
import javax.servlet.ServletContext;
import javax.servlet.http.HttpSession;
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;
public class SeesionLister 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);
}
}

2、具体实现的servlet：

package com.ykh.session;import java.io.IOException;
import java.io.PrintWriter;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;/**
* Servlet implementation class SeesionTest
*/
@WebServlet("/Test")
public class SeesionTest extends HttpServlet {
private static final long serialVersionUID = 1L; /**
* @see HttpServlet#HttpServlet()
*/
public SeesionTest() {
super();
// TODO Auto-generated constructor stub
}/**
* @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
*/
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
// TODO Auto-generated method stub
req.setCharacterEncoding("utf-8");
doPost(req,resp);
}/**
* @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
*/
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
// TODO Auto-generated method stub
//doGet(request, response);
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);
}}