11月8日学习日志

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>"); 
    }
}