Where are cookies stored? Decrypt the data exchange mechanism behind the website

A cookie is a small text file that is stored on the user's computer and is used by web servers to store data on the user's browser. The function of cookies is to store and transfer information when users visit the website to personalize the website and track users.

First, let’s understand where cookies are stored. Cookies can be stored in different locations in the user's browser. Among them, the most common ones are stored on the user's local file system, that is, in a specific folder on the hard disk. Such cookies are called local storage cookies (Local Storage Cookie).
In addition, cookies can also be stored in the browser's memory, that is, temporary memory cookies (Session Cookies). This type of cookie is stored in memory and is only valid during the user's browser session. Once the user closes the browser, these cookies will be cleared.

When deciphering the data exchange mechanism behind the website, we need to understand how cookies work. When a user visits a website for the first time, the web server sends a cookie with a unique identifier to the user's browser. The browser will store this cookie and attach this cookie to the header of the HTTP request and send it to the server the next time the user visits the website. The server can identify the user based on the unique identifier in the cookie and store and read relevant data as needed.

In order to better understand the data exchange mechanism, below we provide a specific code example. Please note that the following examples are based on Java language and Servlet technology.

First, we need to create a Servlet on the web server to receive and process HTTP requests.

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

public class CookieServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws IOException {
        String username = request.getParameter("username");

        // 创建一个Cookie对象
        Cookie cookie = new Cookie("username", username);

        // 将Cookie添加到HTTP响应中
        response.addCookie(cookie);

        response.getWriter().println("Cookie已发送并存储成功！");
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException {
        // 从HTTP请求中获取Cookie
        Cookie[] cookies = request.getCookies();

        if (cookies != null) {
            for (Cookie cookie : cookies) {
                String name = cookie.getName();
                String value = cookie.getValue();
                response.getWriter().println(name + ": " + value);
            }
        } else {
            response.getWriter().println("没有找到Cookie！");
        }
    }
}

In the above code, we receive the user name in the HTTP request in the doPost method and create a Cookie object named "username". We then add the cookie to the HTTP response sent to the user's browser by calling the response.addCookie(cookie) method.

In the doGet method, we get the Cookie array from the HTTP request by calling the request.getCookies() method. We can then iterate through the array, get the name and value of each cookie, and print it to the browser by calling the response.getWriter().println() method.

When a user accesses this Servlet, Cookie information can be stored by sending a POST request with the user name. Afterwards, the stored cookie information can be obtained and printed from the HTTP request by sending a GET request.

It should be noted that the above example only shows the basic usage and data exchange mechanism of Cookie, and does not involve specific encryption and decryption functions. If you need to encrypt and decrypt cookies, you can use some commonly used encryption algorithms and tools.

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