Java我怎么知道会话的最后访问时间？

package org.nhooo.example.servlet;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.Date;

public class SessionLastAccessTime extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        HttpSession session = request.getSession();
        Date date = new Date(session.getLastAccessedTime());

        PrintWriter writer = response.getWriter();
        writer.println("Last accessed time: " + date);
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        doPost(request, response);
    }
}

该servlet将返回如下结果：

Last accessed time: Thu Jan 03 00:47:34 ICT 2008