今天学习了servlet的Session跟踪实例：
本实例说明了如何使用 HttpSession 对象获取 session 会话创建时间和最后访问时间。如果不存在 session 会话，我们将通过请求创建一个新的 session 会话。
package com.runoob.test; import java.io.IOException; import java.io.PrintWriter; import java.text.SimpleDateFormat; import java.util.Date; 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 SessionTrack */ @WebServlet("/SessionTrack") public class SessionTrack extends HttpServlet { private static final long serialVersionUID = 1L; public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { // 如果不存在 session 会话，则创建一个 session 对象 HttpSession session = request.getSession(true); // 获取 session 创建时间 Date createTime = new Date(session.getCreationTime()); // 获取该网页的最后一次访问时间 Date lastAccessTime = new Date(session.getLastAccessedTime()); //设置日期输出的格式 SimpleDateFormat df=new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"); String title = "Servlet Session 实例 - 菜鸟教程"; Integer visitCount = new Integer(0); String visitCountKey = new String("visitCount"); String userIDKey = new String("userID"); String userID = new String("Runoob"); if(session.getAttribute(visitCountKey) == null) { session.setAttribute(visitCountKey, new Integer(0)); } // 检查网页上是否有新的访问者 if (session.isNew()){ title = "Servlet Session 实例 - 菜鸟教程"; session.setAttribute(userIDKey, userID); } else { visitCount = (Integer)session.getAttribute(visitCountKey); visitCount = visitCount + 1; userID = (String)session.getAttribute(userIDKey); } session.setAttribute(visitCountKey, visitCount); // 设置响应内容类型 response.setContentType("text/html;charset=UTF-8"); PrintWriter out = response.getWriter(); String docType = "<!DOCTYPE html>\n"; out.println(docType + "<html>\n" + "<head><title>" + title + "</title></head>\n" + "<body bgcolor=\"#f0f0f0\">\n" + "<h1 align=\"center\">" + title + "</h1>\n" + "<h2 align=\"center\">Session 信息</h2>\n" + "<table border=\"1\" align=\"center\">\n" + "<tr bgcolor=\"#949494\">\n" + " <th>Session 信息</th><th>值</th></tr>\n" + "<tr>\n" + " <td>id</td>\n" + " <td>" + session.getId() + "</td></tr>\n" + "<tr>\n" + " <td>创建时间</td>\n" + " <td>" + df.format(createTime) + " </td></tr>\n" + "<tr>\n" + " <td>最后访问时间</td>\n" + " <td>" + df.format(lastAccessTime) + " </td></tr>\n" + "<tr>\n" + " <td>用户 ID</td>\n" + " <td>" + userID + " </td></tr>\n" + "<tr>\n" + " <td>访问统计：</td>\n" + " <td>" + visitCount + "</td></tr>\n" + "</table>\n" + "</body></html>"); } }