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Cookies and sessions
2022-06-21 18:50:00 【LvhaoIT】
List of articles
One 、Cookie
1. Introduce :
1)Cookie From Servlet A tool class in the specification , Exist in Tomcat Provide servlet-api.jar in
2) If two Servlet From the same website , And for the same browser / Service provided by users , here
With the help of Cookie Object for data sharing
3) Cookie Store the private data of the current user , Improve the quality of service in the process of sharing data
4) In real life situations ,Cookie It is equivalent to that the user gets 【 Membership card 】
2. principle :
For the first time, the user through the browser to MyWeb The website sends a request for OneServlet.
OneServlet Create a Cookie Store data related to the current user
OneServlet After work ,【 take Cookie Write to the response header 】 Return to the current
browser .
After the browser receives the response package , take cookie Cache stored in the browser
After a while , User pass 【 The same browser 】 Again to 【myWeb Website 】 Send request request TwoServlet when .
【 The browser needs to unconditionally myWeb Pushed by the website before Cookie, Write to request header 】 Send past
here TwoServlet At run time , You can read from the request header cookie In the information , obtain OneServlet Provided
Shared data
3. Implement the command :
Same website OneServlet And TwoServlet With the help of Cookie Implement data sharing
OneServlet{
public void doGet(HttpServletRequest request,HttpServletResponse resp){
//1. Create a cookie object , Save shared data （ Current user data ）
Cookie card = new Cookie("key1","abc");
Cookie card1= new Cookie("key2","efg");
****cookie Equivalent to one map
**** One cookie Only one key value pair can be stored in the
**** The key value is right key And value Can only be String
**** The key/value pair key It can't be Chinese
//2.【 Hairpin 】 take cookie Write to the response header , Give it to the browser
resp.addCookie(card);
resp.addCookie(card1)
}
}
browser / user <--------- Response package 【200】
【cookie: key1=abc; key2=eft】
【】
【 Processing results 】
Browser direction myWeb The website sends a request to visit TwoServlet----> Request package 【url:/myWeb/two method:get】
【
Request parameters ：xxxx
Cookie key1=abc;key2=efg
】
【】
【】
TwoServlet{
public void doGet(HttpServletRequest request,HttpServletResponse resp){
//1. Call the request object to get the returned from the browser from the request header Cookie
Cookie cookieArray[] = request.getCookies();
//2. Loop through the data to get each cookie Of key And value
for(Cookie card:cookieArray){
String key = card.getName(); Read key "key1"
Strign value = card.getValue(); Read value "abc"
Provide better service ........
}
}
}
4.Cookie Destruction opportunity :
1. By default ,Cookie Objects are stored in the browser's cache .
So as long as the browser closes ,Cookie The object is destroyed
2. In case of manual setting , You can ask the browser to receive Cookie
Stored on the hard disk of the client computer , At the same time, you need to specify Cookie
Survival time on hard disk . Within the lifetime , Close the browser
Shut down the client computer , Shut down the server , It doesn't lead to Cookie
Be destroyed . When the survival time arrives ,Cookie Automatically from the hard disk
Delete
cookie.setMaxAge(60); //cookie Survive on the hard disk 1 minute
5.Cookie understand ：
* First of all, for Cookie,cookie It's not safe , It can be modified artificially
* need Cookie If your page doesn't get Cookie Parameters , Will report 500 wrong
* Cookie It will be destroyed when the browser is closed
6.Cookie example —— Ordering membership card
oneServlet
public class oneServlet extends javax.servlet.http.HttpServlet {
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
}
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//1. Call the request object to read 【 Request parameters 】 Information
String userName, money;
userName = request.getParameter("userName");
money = request.getParameter("money");
//2. activate a bank card
Cookie card1 = new Cookie("userName", userName);
Cookie card2 = new Cookie("money", money);
//3. Hairpin , take Cookie Write to the response header and give it to the browser
response.addCookie(card1);
response.addCookie(card2);
//4. Notify the browser to write the content of the order page into the response body and give it to the browser （ Request forwarding ）
request.getRequestDispatcher("/index_2.html").forward(request, response);
}
}
twoServlet
/** * Created by IntelliJ IDEA. * User: LvHaoIT (asus) * Date: 2021/5/5 * Time: 14:14 */
public class twoServlet extends HttpServlet {
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
}
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
double jiaozi_money = 30;
double gaifan_money = 21;
double miantiao_money = 20;
double money = 0;
double xiaofei = 0;
String food, userName = null;
// Modify the response body character set
response.setContentType("text/html;charset=utf-8");
// Get output stream object
PrintWriter out = response.getWriter();
// Define a new Cookie, Overwrite the previous with the newly processed value cookie
Cookie newCard = null;
//1. Read request header parameter information , Get the type of food the user ordered
food = request.getParameter("food");
//2. Read... In the request Cookie
Cookie[] cookieArray = request.getCookies();// Remove all cookie
//3. Credit card consumption
for (Cookie card : cookieArray) {
// Take out the data and process it accordingly
String key = card.getName();// obtain key
String value = card.getValue();// obtain value
// Determine whether the retrieved user name is the user name
if (key.equals("userName")) {
// Is the user name
userName = value;// Find the corresponding user name
} else if (key.equals("money")) {
// What you take out is money
money = Double.valueOf(value); // Save your money
// Start spending food There is the name of the food
if (food.equals(" dumplings ")) {
// I ordered dumplings , But we need to judge whether the money is enough
if (money < jiaozi_money) {
out.print(" user " + userName + " Lack of balance , Please top up ！");
} else {
// Enough money , Can consume
newCard = new Cookie("money", (money - jiaozi_money) + "");
xiaofei = jiaozi_money;
}
} else if (food.equals(" noodles ")) {
// I ordered dumplings , But we need to judge whether the money is enough
if (money < jiaozi_money) {
out.print(" user " + userName + " Lack of balance , Please top up ！");
} else {
// Enough money , Can consume
newCard = new Cookie("money", (money - miantiao_money) + "");
xiaofei = miantiao_money;
}
} else if (food.equals(" Cover rice ")) {
// I ordered dumplings , But we need to judge whether the money is enough
if (money < jiaozi_money) {
out.print(" user " + userName + " Lack of balance , Please top up ！");
} else {
// Enough money , Can consume
newCard = new Cookie("money", (money - gaifan_money) + "");
xiaofei = gaifan_money;
}
}
}
}
//4. Return the user's membership card
response.addCookie(newCard);
//5. The consumption record is written to the response object
out.println(" user " + userName + " This consumption ：" + xiaofei + " The balance in the card remains ：" + (money - xiaofei));
}
}
Test the web ：
index.html
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title> New users open cards </title>
</head>
<body>
<center>
<font style="color: red;font-size:40px ;"> New members open cards </font>
<form action="/myCookie/one" method="GET">
<table border="2">
<tr>
<td>
user name ：
</td>
<td>
<input type="text" name="userName"/>
</td>
</tr>
<tr>
<td>
Deposit amount ：
</td>
<td>
<input type="text" name="money"/>
</td>
</tr>
<tr>
<td>
<input type="submit" value=" Apply for a card "/>
</td>
<td>
<input type="reset" name=" Reset "/>
</td>
</tr>
</table>
</form>
</center>
</body>
</html>
index_2.html
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title> Order page </title>
</head>
<body>
<center>
<font style="color: red;font-size: 40px;"> Order page </font>
<form action="/myCookie/two">
Type of food ：
<input type="radio" name="food" value=" dumplings " /> dumplings （30 element ）<br>
<input type="radio" name="food" value=" noodles " /> noodles （20 element ）<br>
<input type="radio" name="food" value=" Cover rice " /> Cover rice （21 element ）<br>
<input type="submit" value=" Membership card consumption " />
</form>
</center>
</body>
</html>
Implementation schematic diagram
Two 、HttpSession Interface :
1. Introduce ：
1）HttpSession Interface from Servlet Standardize the next interface . Exist in Tomcat in servlet-api.jar
Its implementation class consists of Http Provided by the server .Tomcat The provided implementation class exists in servlet-api.jar
2） If two Servlet From the same website , And for the same browser / Service provided by users , here
With the help of HttpSession Object for data sharing
3） Developers are used to putting HttpSession Interface decorated objects are called 【 Session scope object 】
2.HttpSession And Cookie difference ：【 Interview questions 】
1） Storage location : One in the sky , One is underground
Cookie： Stored on the client computer （ Browser memory / Hard disk ）
HttpSession： Stored in the server computer memory
2） data type ：
Cookie Object storage shared data type can only be String
HttpSession Object can store any type of shared data Object
3) Number of data :
One Cookie Object can only store one shared data
HttpSession Use map Collections store shared data , So you can
Store any amount of shared data
4） object of reference :
Cookie It is equivalent to the customer on the server side 【 Membership card 】
HttpSession It is equivalent to the customer on the server side 【 Private safe 】
3. Command implementation : Same website （myWeb） Next OneServlet Transfer data to TwoServlet
OneServlet{
public void doGet(HttpServletRequest request,HttpServletResponse response){
//1. Call the request object to Tomcat Ask for the private locker of the current user on the server
HttpSession session = request.getSession();
//2. Add data to the user's private locker
session.setAttribute("key1", Shared data )
}
}
Browser access /myWeb in TwoServlet
TwoServlet{
public void doGet(HttpServletRequest request,HttpServletResponse response){
//1. Call the request object to Tomcat Ask for the private locker of the current user on the server
HttpSession session = request.getSession();
//2. Get... From the session scope object OneServlet Shared data provided
Object Shared data = session.getAttribute("key1");
}
}
4.Http How the server connects users to HttpSession Connect
cookie
**5.getSession() And getSession(false)** difference
1）getSession(): If the current user already has his own private locker on the server .
requirement tomcat Return this private locker
If the current user is on the server Not owned yet Own personal lockers
requirement tocmat For the current user Create a New private lockers
2)getSession(false): If the current user already has his own private locker on the server .
requirement tomcat Return this private locker
If the current user is on the server Not owned yet Own personal lockers
here Tomcat take return null
6.HttpSession Destruction opportunity :
1. Users and HttpSession Used in association Cookie Can only be stored in the browser cache .
2. When the browser closes , It means that the user and his HttpSession The relationship is cut off
3. because Tomcat Unable to detect when the browser closes , Therefore, when the browser is closed, it will not
Lead to Tomcat Associate the browser with HttpSession To destroy
4. To solve this problem ,Tomcat For every one HttpSession Object settings 【 free time 】
This idle time defaults to 30 minute , If at present HttpSession Object idle time reached 30 minute
here Tomcat Think users have given up their HttpSession, here Tomcat Will destroy
Drop this HttpSession
7.HttpSession Idle time is manually set
On the current website /web/WEB-INF/web.xml
<session-config>
<session-timeout>5</session-timeout>
<!-- Every in the current website session Maximum free time 5 minute -->
</session-config>
Implementation examples
oneServlet
/** * Created by IntelliJ IDEA. * User: LvHaoIT (asus) * Date: 2021/5/5 * Time: 16:59 */
public class oneServlet extends HttpServlet {
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//1. Call request object , Read request header parameters
String goodsName;
request.setCharacterEncoding("utf-8");
goodsName = request.getParameter("goodsName");
System.out.println(" Entered a breakpoint 1！！");
//2. Call request object , towards tomcat Ask for a private locker
HttpSession session = request.getSession();
//3. Add the items purchased by the user to the current private locker
Integer goodsNum = (Integer) session.getAttribute(goodsName);// Take the quantity of goods
// Judge whether the product is put in for the first time
if (goodsNum == null) {
session.setAttribute(goodsName, 1);
} else {
// There was , Then add one
session.setAttribute(goodsName, goodsNum + 1);
}
}
}
twoServlet
/** * Created by IntelliJ IDEA. * User: LvHaoIT (asus) * Date: 2021/5/5 * Time: 17:11 */
public class twoServlet extends HttpServlet {
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
}
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//1. Call request object , towards tomcat Ask for the private locker of the current user on the server
HttpSession session = request.getSession();
System.out.println(" Entered a breakpoint 2！！");
//2. take session All of the key out , Stored in an enumeration object
Enumeration goodNames = session.getAttributeNames();
//hasMoreElements() If and only if this enumeration object also contains at least one providable element , To return to true; Otherwise return to false.
while (goodNames.hasMoreElements()) {
//E nextElement()
// If this enumeration object has at least one element available , The next element of this enumeration .
String goodName = (String) goodNames.nextElement();// Take out the next trade name
int goodsNum = (int) session.getAttribute(goodName);// Take the number of pieces corresponding to the product name
System.out.println(" Name of commodity ：" + goodName + " The number ：" + goodsNum);
}
}
}
Test the web
index.html
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Title</title>
</head>
<body>
<table border="2" align="center">
<tr>
<td> Name of commodity </td>
<td> item pricing </td>
<td> Supplier </td>
<td> Put it in the shopping cart </td>
</tr>
<tr>
<td> Huawei laptop pro13</td>
<td>7000</td>
<td> Huawei </td>
<td><a href="/myweb/one?goodsName= Huawei laptop pro13"> Put it in the shopping cart </a></td>
</tr>
<tr>
<td> durian </td>
<td>200</td>
<td> Thailand </td>
<td><a href="/myweb/one?goodsName= durian "> Put it in the shopping cart </a></td>
</tr>
<tr>
<td> Men's underwear </td>
<td>1000</td>
<td> Zhufangcheng </td>
<td><a href="/myweb/one?goodsName= Men's underwear "> Put it in the shopping cart </a></td>
</tr>
<tr align="center">
<td colspan="4">
<a href="/myweb/two"> Check out my shopping cart </a>
</td>
</tr>
</table>
</body>
</html>
Implementation schematic diagram ：
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