Cookie learning diary 1

Catalog

One 、 State management

1.1 Existing problems

1.2 Concept

1.3 State management classification

Two 、Cookie Use

2.1 What is? Cookie

2.2 establish Cookie

 2.3  obtain Cookie

2.4 modify Cookie

2.5 Cookie Encoding and decoding

2.6 Cookie pros and cons

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One 、 State management

1.1 Existing problems

HTTP Protocol is stateless , Can't save information submitted every time

If the user sends a new request , The server cannot know if it is connected to the last request .

For those that need to submit data multiple times to complete Web operation , For example, login , It's a problem .

1.2 Concept

Will browser and web Multiple interactions between servers are handled as a whole , And the data involved in multiple interactions （ I.e. status ） preserved .

1.3 State management classification

Client state management technology : Save state on client . The representative is Cookie technology .

Server state management technology : Save the state on the server side . The representative is session technology （ Server delivery sessionID When needed Cookie The way ） and application

Two 、Cookie Use

2.1 What is? Cookie

Cookie It's in the browser Web When a resource of the server , from Web The server HTTP The response header is accompanied by a small piece of data transmitted to the browser .

once Web The browser saved some Cookie, Then every time it visits the Web Server time , Should be in HTTP This is in the request header Cookie Send it back to Web The server .

One Cookie Mainly by the name that identifies the information (name) And the value (value) form .

 

2.2 establish Cookie

1、 establish

package com.ha.cookie;

import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class CookieServlet extends HttpServlet{

    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doPost(req, resp);
    }

    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        // 1、 Server creation Cookie object 
        Cookie cookie = new Cookie("username", "HuAn");

        // 2、 take Cookie Respond to clients 
        resp.addCookie(cookie);
    }
}

<?xml version="1.0" encoding="UTF-8"?>

<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee
                      http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd"
  version="3.1"
  metadata-complete="true">

  <servlet>
    <servlet-name>ck</servlet-name>
    <servlet-class>com.ha.servlet.CookieServlet</servlet-class>
  </servlet>

  <servlet-mapping>
    <servlet-name>ck</servlet-name>
    <url-pattern>/ck</url-pattern>
  </servlet-mapping>

</web-app>

2、 see

Run and visit this page

（1） Check mode 1 ：

There is a response in the response header cookie

 

（2） View mode 2

 

3、 Add

（1） Set the access path

 

（2） Set up the client cookie Valid time

 

（3） Set up multiple cookie

 

 2.3  obtain Cookie

package com.ha.cookie;

import javax.servlet.ServletException;
import javax.servlet.http.*;
import java.io.IOException;
import java.net.URLDecoder;

public class GetServlet extends HttpServlet {

    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //1. adopt request Object to get all cookie
        Cookie[] cookies = req.getCookies();
        //2. Through the loop traversal Cookie
        if(cookies!=null){
            for(Cookie cookie : cookies){
                System.out.println(URLDecoder.decode(cookie.getName(),"UTF-8") +":"+URLDecoder.decode(cookie.getValue(),"UTF-8"));
            }
        }
    }

    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req,resp);
    }
}

 ​​​​​​​

 

2.4 modify Cookie

Just make sure that Cookie If the name and path of the are consistent, you can modify

Cookie cookie = new Cookie("username", "Tom");
cookie.setPath("/myweb");
cookie.setMaxAge(60*60);
resp.addCookie(cookie);

Be careful ： If you change cookie Of name And valid paths will be created cookie, And change cookie value 、 The validity period will cover the original cookie

 

2.5 Cookie Encoding and decoding

Cookie Chinese is not supported by default , Can only contain ASCI character , therefore Cookie Need to be right Unicode The characters are encoded , Otherwise, there will be confusion .

Coding can use java.net.URLEncoder Class encode(String str, String encoding) Method

Decode using java.net.URLDecoder Class decode(String str, String encoding) Method

 

 

 

2.6 Cookie pros and cons

1、 advantage ：

         Configurable expiration rules .

         simplicity : Cookie Is a text-based lightweight structure , Contains simple key value pairs .

         Data persistence : Cookie By default, it can be one before expiration - It has been stored on the client browser

2、 shortcoming :

         Size Limited : Most browsers are right Cookie The size of 4K、8K word Section restrictions .

         The user is configured to disable : Some users disable browser or client device reception Cookie The ability of , So it limits this function .

         Potential security risks : Cookie May be tampered with . May pose a potential risk to security or lead to reliance on Cookie The application for failed .