Example: Remember the last access time 1. Requirements: 1. Access a Servlet. 2. If it is not the first time, the system displays a message: Welcome back. The last time you accessed the system is: Displays the time string

The Servlet in the server determines whether there is a Cookie named lastTime. 1. There are: not first access 1. Response data: Welcome back, you last accessed: June 10, 2018 11:50:20 2. Write back to Cookie: lastTime= jun 10, 2018 11:50:01 2. 1. Response data: Hello, welcome to your first visit 2. Write back to Cookie: lastTime= June 10, 2018 11:50:01Copy the 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.URLDecoder;
import java.net.URLEncoder;
import java.text.SimpleDateFormat;
import java.util.Date;

@WebServlet("/cookieTest")
public class CookieTest extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // Set the data format and encoding of the message body of the response
        response.setContentType("text/html; charset=utf-8");

        //1. Get all cookies
        Cookie[] cookies = request.getCookies();
        boolean flag = false;// No cookie is lastTime
        //2. Iterate over the cookie array
        if(cookies ! =null && cookies.length > 0) {for (Cookie cookie : cookies) {
                //3. Get the name of the cookie
                String name = cookie.getName();
                //4. Check whether the name is lastTime
                if("lastTime".equals(name)){
                    // There is this Cookie, not the first access

                    flag = true;// There is a lastTime cookie

                    // Set the value of the Cookie
                    // Get the current time string, reset the value of the Cookie, resend the Cookie
                    Date date  = new Date();
                    // Convert the format
                    SimpleDateFormat sdf = new SimpleDateFormat("Yyyy yyyy MM dd day HH: MM :ss");
                    String str_date = sdf.format(date);
                    cookie.setValue(str_date);
                    // Sets the lifetime of the cookie
                    cookie.setMaxAge(60 * 60 * 24 * 30);/ / for a month
                    response.addCookie(cookie);// Resend the cookie


                    // Response data
                    // Get the Cookie value, time
                    String value = cookie.getValue();
                    response.getWriter().write("
 Welcome back, you last visited at :"+value+"</h1>");
                    break; }}}if(cookies == null || cookies.length == 0 || flag == false) {// No, first visit

            // Set the value of the Cookie
            // Get the current time string, reset the value of the Cookie, resend the Cookie
            Date date  = new Date();
            SimpleDateFormat sdf = new SimpleDateFormat("Yyyy yyyy MM dd day HH: MM :ss");
            String str_date = sdf.format(date);
          
            Cookie cookie = new Cookie("lastTime",str_date);
            // Sets the lifetime of the cookie
            cookie.setMaxAge(60 * 60 * 24 * 30);/ / for a month
            response.addCookie(cookie);

            response.getWriter().write("< H1 > Hello, welcome to your first visit to "); }}protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request, response); }}Copy the code

Character [32] ASCII Chinese space “YYYY year MM month DD day HH: MM :ss” contains Spaces

Before Tomcat 8, Chinese data could not be stored directly in cookies. Chinese data needs to be transcoded - generally using URL encoding (%E3) after Tomcat 8, cookies support Chinese data. Str_date = urlencoder. encode(str_date, "UTF-8"); str_date = URLEncoder. Encoding. Use value = urldecoder.decode (value, "UTF-8"); Decoding.Copy the code

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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.URLDecoder;
import java.net.URLEncoder;
import java.text.SimpleDateFormat;
import java.util.Date;

@WebServlet("/cookieTest")
public class CookieTest extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // Set the data format and encoding of the message body of the response
        response.setContentType("text/html; charset=utf-8");

        //1. Get all cookies
        Cookie[] cookies = request.getCookies();
        boolean flag = false;// No cookie is lastTime
        //2. Iterate over the cookie array
        if(cookies ! =null && cookies.length > 0) {for (Cookie cookie : cookies) {
                //3. Get the name of the cookie
                String name = cookie.getName();
                //4. Check whether the name is lastTime
                if("lastTime".equals(name)){
                    // There is this Cookie, not the first access

                    flag = true;// There is a lastTime cookie

                    // Set the value of the Cookie
                    // Get the current time string, reset the value of the Cookie, resend the Cookie
                    Date date  = new Date();
                    // Convert the format
                    SimpleDateFormat sdf = new SimpleDateFormat("Yyyy yyyy MM dd day HH: MM :ss");
                    String str_date = sdf.format(date);
                    System.out.println("Before coding:"+str_date);
                    / / URL encoding
                    str_date = URLEncoder.encode(str_date,"utf-8");
                    System.out.println("After coding:"+str_date);
                    cookie.setValue(str_date);
                    // Sets the lifetime of the cookie

                    cookie.setMaxAge(60 * 60 * 24 * 30);/ / for a month
                    response.addCookie(cookie);// Resend the cookie


                    // Response data
                    // Get the Cookie value, time
                    String value = cookie.getValue();
                    System.out.println("Before decoding:"+value);
                    / / URL decoding:
                    value = URLDecoder.decode(value,"utf-8");
                    System.out.println("After decoding:"+value);
                    response.getWriter().write("
 Welcome back, you last visited at :"+value+"</h1>");

                    break; }}}if(cookies == null || cookies.length == 0 || flag == false) {// No, first visit

            // Set the value of the Cookie
            // Get the current time string, reset the value of the Cookie, resend the Cookie
            Date date  = new Date();
            SimpleDateFormat sdf = new SimpleDateFormat("Yyyy yyyy MM dd day HH: MM :ss");
            String str_date = sdf.format(date);
            System.out.println("Before coding:"+str_date);
            / / URL encoding
            str_date = URLEncoder.encode(str_date,"utf-8");
            System.out.println("After coding:"+str_date);

            Cookie cookie = new Cookie("lastTime",str_date);
            // Sets the lifetime of the cookie
            cookie.setMaxAge(60 * 60 * 24 * 30);/ / for a month
            response.addCookie(cookie);

            response.getWriter().write("< H1 > Hello, welcome to your first visit to "); }}protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request, response); }}Copy the code