Cookie 之显示用户上次访问时间

错误代码：

    String currentTime = new SimpleDateFormat("yyyy-MM-dd hh:mm:ss")
                    .format(new Date());
            Cookie cookie = new Cookie("lastAccess",currentTime);

正确代码：

   Cookie cookie = new Cookie("lastAccess",System.currentTimeMillis()+"");

完整代码：

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

public class LastAccessServlet extends HttpServlet {
    public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // 指定服务器输出内容的编码方式UTF-8，防止发生乱码
        response.setContentType("text/html;charset=utf-8");
        String lastAccessTime = null;
        // 获取所有的cookie，并将这些cookie存放在数组中
        Cookie[] cookies = request.getCookies();
        PrintWriter out = response.getWriter();
        long time = 0;
        // 遍历cookies数组
        for (int i = 0; cookies != null && i<cookies.length; i++) {
            Cookie c = cookies[i];
            if ("lastAccess".equals(c.getName())) {
                // 如果cookie的名称为lastAccess,则获取该cookie的值
                lastAccessTime = c.getValue();
                 time = Long.parseLong(lastAccessTime);
                break;
            }
        }
        // 判断是否存在名称为lastAccess的cookie
        if (lastAccessTime == null) {
            out.print("您是首次访问本站！！！");
        } else {
            out.print("您上次的访问时间是： " + new Date(time).toLocaleString());
        }
        Cookie cookie = new Cookie("lastAccess",System.currentTimeMillis()+"");
        //cookie.setMaxAge(60*60); //设置cookie最大存在时间
        // 发送 cookie
        response.addCookie(cookie);
    }
    public void doPost(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException {
        this.doPost(req, resp);
    }
}

总结：没有完全弄懂第一种方式为什么错了，两种获取时间的方式为什么不同，求指教啊~~