28, cookie achieve memory Last

Case: Remember the last access time
        1. Requirements:
            1. Access a Servlet, if it is the first visit, the prompt: Hello, welcome to your first visit.
            2. If it is not the first visit, the prompt: Welcome back, your last visit time: displays the time string

        2. Analysis:
            1. Cookie can be accomplished using
            2. Servlet in the server to determine whether there is a file called lastTime of the cookie
                1 are: not the first visit to
                    1. response data: Welcome back, your last visit time: June 10, 2018 11:50:20
                    2. write back Cookie: lastTime = 2018 Nian 6 Yue 10 11:50:01
                2. no: is the first visit to
                    1. The response data: Hello, welcome to your first visit
                    2. write back Cookie: lastTime = 2018 Nian 6 Yue 10, 11:50:01

Code:

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
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.net.URL;
import java.net.URLDecoder;
import java.net.URLEncoder;
import java.text.SimpleDateFormat;
import java.util.Date;

@WebServlet("/ServletCookitTest")
public class ServletCookitTest extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doGet(request, response);
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        response.setContentType("text/html;charset=utf-8");

        //从请求中获取cookits
        Cookie[] cs = request.getCookies();
        boolean firstFlag = true;
        for (Cookie c : cs) {
            String name = c.getName();
            if ("lastLoginTime".equals(name)){

                firstFlag = false;//不是第一次登录
                //获取上次登录时间
                String lastDate = c.getValue();
                //转换成能够识别码
                lastDate = URLDecoder.decode(lastDate, "utf-8");


                //获取当前时间
                Date date = new Date();
                SimpleDateFormat sdf = new SimpleDateFormat("yy年MM月dd HH:mm:ss");
                String formatDate = sdf.format(date);
                //tomcat8.0以上可以识别中文字符，但是不能识别特殊字符，因此要进行URL转码
                String URL_Date = URLEncoder.encode(formatDate, "utf-8");

                //将用日期设定的cookit的返回去
                c.setValue(URL_Date);
                //设置存活时间
                c.setMaxAge(60*60*24*30);//缓冲30天

                //
                response.addCookie(c);

                //获取上次的登录时间
                response.getWriter().write("<h1>欢迎您回来，上次登录时间是：" + lastDate+"</h1>");

                break; //已经查到了，就跳出循环
            }
        }

        if (firstFlag){

            //获取当前时间
            Date date = new Date();
            SimpleDateFormat sdf = new SimpleDateFormat("yy年MM月dd HH:mm:ss");
            String formatDate = sdf.format(date);
            //tomcat8.0以上可以识别中文字符，但是不能识别特殊字符，因此要进行URL转码
            String URL_Date = URLEncoder.encode(formatDate, "utf-8");

            Cookie c = new Cookie("lastLoginTime", URL_Date);

            response.addCookie(c);

            //获取上次的登录时间
            response.getWriter().write("<h1>您是首次登录，欢迎您的访问！</h1>");
        }
    }
}

test:

Display for the first time can only be displayed once, if you want to retest the cookie will perform setMaxAge (0), and then change it back.