维护当前用户和Web应用的状态通过以下两种方式实现：
一种是通过Cookie方式实现，一种是通过Session方式实现。
Cookie通过在客户端保存用户的信息，每次服务器端回去读取客户端的Cookie中的信息。
Session通过两种方式实现：
一种是把一个名为JSESSIONID的十六进制数字的信息保存到Cookie中标识每一个访问的用户。
一种是通过URL重写的方式就是把每个用户的jsessionid的值附加到URL中，实现会话功能。
HttpSessionTest
import java.io.IOException;
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 HttpSessionTest extends HttpServlet
{
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException
{
HttpSession session = request.getSession();
Integer count = (Integer) session.getAttribute("counter");
if (count == null)
{
count = 1;
}
else
{
count++;
}
session.setAttribute("counter", new Integer(count));
request.getRequestDispatcher("/count.jsp").forward(request, response);
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException
{
doGet(request, response);
}
}
count.jsp
<%@ page language="java" contentType="text/html; charset=GBK"
pageEncoding="GBK" session="true"%>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>访问量统计</title>
</head>
<body>
<%
HttpSession httpSession = request.getSession();
Integer count = (Integer)httpSession.getAttribute("counter");
out.println("当前访问量为："+count);
%>
</body>
</html>