Java Web Cookie details
What is a cookie?
Query Youdao Dictionary:
What does the Web have to do with cookies?
The answer to this riddle and so on
Session technology
Session technology in the Web is similar to a real life chat between two people, except that a session in the Web refers to the interaction between a server and a client
A session consists of multiple requests and responses, established when the browser sends a request to the server, and ended when one party disconnects.functionWhat does it mean that data can be shared between multiple requests within the scope of a session
1. In browsers, there is often an exchange of data, such as when you log on to a page. We often set up automatic login options. So they remember our information through cookies, cookies are made by THE HTTP server, stored in the browser, but HTTP protocol is a stateless protocol, after the data exchange, the server and the client will be closed, each time the exchange of data need to establish a new link. Just like when we go to the supermarket to buy something without the integral card, after we buy something, the supermarket does not have any of our consumption information, but after we get the integral card, the supermarket has our consumption information. Cookies are like scorecards, which can save points. Goods are our information. The supermarket system is like the server background, and HTTP protocol is the transaction process.
2. Many websites now use new users to register this, sometimes register, wait until the next visit to the site, will automatically recognize you, and post to say hello to you, do not feel very cordial? Of course, such a function of knowledge surface phenomenon, more importantly, the website can use cookies to track the habits of users to visit the website, such as when to visit, which pages to visit, stay in each page and so on. Using this information, on the one hand, can provide personalized services for users, on the other hand, can also be used as a tool to understand all user behavior, for the improvement of website business strategy has certain reference value. , for example, you are in an airline site check flight schedule, the site might be created containing your Cookies, travel plan might it only recorded the you once visited Web pages on the site, when the next time you visit, to the content of the website according to your circumstance to adjust, on top of the content of the you’re interested in. This is an advanced COokie application.
The concept of cookies
Is a client session technique that saves data to the client
The advantages and disadvantages of cookies are as follows: 1. It is very convenient to save the data to the client and reduce the storage pressure of the server. 2. Limits on the number (20) and size (4KB) of data to be saved
Function cookie is used to save a small amount of and less sensitive data can be in the case of no login, to complete the identity of the client (that is, set a set-cookie key-value pair on the client, use key-value pair to obtain the identity of the client when accessing)
How to use cookies
I introduce the use of cookie from the following three steps: 1. Create cookie object 2. 3. Get the cookie. The cookie is set by Servlet1, and Servlet2 gets the cookie
Servlet1
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;
@WebServlet("/demo1")
public class Servlet1 extends HttpServlet {
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
/ / create a cookie
Cookie cookie = new Cookie("name"."zhangsan");
resp.addCookie(cookie);
}
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
this.doPost(req, resp); }}Copy the codeServlet2
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;
@WebServlet("/demo2")
public class Servlet2 extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
/ / get a cookie
Cookie[] cookies = req.getCookies();
if(cookies! =null) {for (Cookie cookie : cookies) {
// Get the cookie value and name
String value = cookie.getValue();
String name = cookie.getName();
System.out.println(name+"："+value); }}}@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
this.doGet(req, resp); }}Copy the codeIn response to a cookie
Request cookies, the other two cookies we won’t cover here
Illustration:
Questions about cookies
How to send multiple cookies 2. How long can cookies be saved in the browser 3. How to save Cookies in Chinese 4
1. How to send multiple cookies
The cookie can be sent by calling the addCookie method using the Response object
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;
@WebServlet("/demo1")
public class Servlet1 extends HttpServlet {
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
/ / create a cookie
// Create the first cookie
Cookie cookie = new Cookie("name"."zhangsan");
// Send the first cookie
resp.addCookie(cookie);
// Create a second cookie
Cookie id = new Cookie("id"."1");
// Send the second cookie
resp.addCookie(id);
}
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
this.doPost(req, resp); }}Copy the codeimport 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;
@WebServlet("/demo2")
public class Servlet2 extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
/ / get a cookie
Cookie[] cookies = req.getCookies();
// Iterate over the cookie array
if(cookies! =null) {for (Cookie cookie : cookies) {
// Get the cookie value and name
String value = cookie.getValue();
String name = cookie.getName();
System.out.println(name+"："+value); }}}@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
this.doGet(req, resp); }}Copy the codeClient display 
The IDEA of printing 
2. How long can cookies be saved in the browser
Setmaxage (int seconds) setMaxage (int seconds) setMaxage (int seconds) setMaxage (int seconds) Second is less than zero. The default value is that the cookie is deleted after the browser is closed
3. How to save cookies in Chinese
- Before Tomcat 8, Chinese data could not be stored directly in cookies.
Need to transcode Chinese data — generally URL encoding (%E3)
- After Tomcat 8, cookies support Chinese data.
Special characters are still not supported. You are advised to use URL encoding for storage and URL decoding and parsing
For example, if I use the following code to add data to the Cookie and send the Cookie, the browser will report an error because I added a space to the Cookie
Cookie cookie = new Cookie("name"."Zhang");
// Send the first cookie
resp.addCookie(cookie);
Copy the code
So I need to use URL encoding to control the data
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;
@WebServlet("/demo1")
public class Servlet1 extends HttpServlet {
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
// Set the data format and encoding of the message body of the response
resp.setContentType("text/html; charset=utf-8");
/ / create a cookie
// Create the first cookie
String name="Zhang";
/ / URL encoding
name= URLEncoder.encode(name,"utf-8");
Cookie cookie = new Cookie("name", name);
resp.addCookie(cookie);
}
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
this.doPost(req, resp); }}Copy the codeimport 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;
@WebServlet("/demo2")
public class Servlet2 extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
/ / get a cookie
Cookie[] cookies = req.getCookies();
// Iterate over the cookie array
if(cookies! =null) {for (Cookie cookie : cookies) {
// Get the cookie value and name
String value = cookie.getValue();
String name = cookie.getName();
/ / decoding
System.out.println(name+"："+value);
/ / after decoding
System.out.println(name+":"+ URLDecoder.decode(value,"utf-8")); }}}@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
this.doGet(req, resp); }}Copy the codeResults:
No longer an error
4.Cookie sharing problem
By default, cookies cannot be shared among web projects deployed on a Tomcat server. However, we can call setPath () to set the cookie range. By default, the current virtual directory is set. You can set path to “/”
// Set the data format and encoding of the message body of the response
resp.setContentType("text/html; charset=utf-8");
/ / create a cookie
// Create the first cookie
String name="张 三";
/ / URL encoding
name= URLEncoder.encode(name,"utf-8");
Cookie cookie = new Cookie("name", name);
// Set path to share cookie information with all projects deployed under the current server
// Set it to "/" to share
cookie.setPath("/");
resp.addCookie(cookie);
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Cookie sharing problem between different Tomcat servers? * setDomain(String path): If the first level domain is set to the same, Therefore, cookies can be shared between multiple servers * setDomain(“.baidu.com”), and cookies can be shared between tieba.baidu.com and news.baidu.com
// Set the data format and encoding of the message body of the response
resp.setContentType("text/html; charset=utf-8");
/ / create a cookie
// Create the first cookie
String name="张 三";
/ / URL encoding
name= URLEncoder.encode(name,"utf-8");
Cookie cookie = new Cookie("name", name);
// Set path so that cookie information can be shared between different servers
// If the domain name is ".baidu.com", cookies can be shared
cookie.setDomain(".baidu.com");
resp.addCookie(cookie);
Copy the codeIf there are mistakes, please also criticize and correct, writing is not easy, like also please point a like, if there are questions, comments, I will often update the article, read the article feel helpful can pay attention to me
