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Cookies and sessions

2022-07-29 02:14:00 【TPH-BETTER】

video https://www.bilibili.com/video/BV1UV411r7fW?p=1&vd_source=3558fd85254f40ca0361146cc92d2cce

One 、 Conversational Technology

1、 conversation ： A session contains multiple requests and responses
One session ： The first time a browser sends a request to a server resource , Session creation , Until one side is disconnected
2、 function ： Between multiple requests within the scope of a session , Shared data

3、 The way ：

Client session technology ：Cookie
Server side session technology ：Session

Two 、Cookie

1. Concept

Concept ： Client session technology , Save data to client

2. Quick start

Quick start （ Use steps ）：
1、 establish Cookie object , Data binding

new Cookie(String name,String value)

2、 send out Cookie object

response.addCookie(Cookie cookie)

3、 obtain Cookie, Get the data

Cookie[ ] request.getCookies()

3. Cookie The details of the

3.1 Can I send more than one at a time Cookie？

Sure , You can create multiple Cookie object , Use response Call several times addCookie Method to send Cookie that will do .

3.2 Cookie How long to save in the browser

1、 By default , When the browser is closed ,Cookie The data is destroyed
2、 Persistent storage
setMaxAge(int seconds)

Positive numbers ： take Cookie The data is written to a file on the hard disk , Persistent storage . And designate Cookie Survival time , After the time ,Cookie The file is automatically invalidated
negative ： The default value is （ When the browser is closed ,Cookie The data is destroyed ）
zero ： Delete Cookie Information

3、cookie Can you save Chinese

stay tomcat 8 Before cookie Can't store Chinese data directly in （ Need to transcode Chinese data — It is generally used URL code （%E3）)
stay tomcat after ,Cookie Support Chinese data

4、cookie Sharing issues ？
1、 Suppose it's in a tomcat Server , Deployed multiple Web project , So in these Web In the project cookie Can we share ？

By default ,cookie Cannot share
setPath(String path)： Set up cookie The scope of acquisition , By default , Set the current virtual directory , If you need to share , Then you can put path Set to “/”

5、 Different tomcat Server room cookie Sharing issues ？

setDomain(String path)： If the primary domain name is the same , So many servers cookie Can be Shared
example ：setDomain(“.baidu.com”), that tieba.baidu.com and news.baidu.com in cookie Can be Shared

3、 ... and 、JSP Introduction learning

1. Concept

JSP：Java Server Pages：java Server side page

It can be understood as ： A special page , You can specify html label , You can also define java Code
Used to simplify writing

JSP It's essentially one Servlet

2. Use

JSP Script for ：JSP Definition Java The way the code works

<% Code %>： Defined java Code , stay service In the method ,service What can be defined in the method , The script can define what .
<%! Code %>： Defined javadiam, stay jsp Converted java Class member location
<%= Code %>： Defined java Code , Will be output to the page . What can be defined in the output statement , The script can define what

JSP Built in objects for
stay jsp There is no need to get and create , Objects that can be used directly

stay jsp There's a total of 9 Built in objects

Let's start with three ：

request
response
out： Character output stream object , You can output data to the page , and response.getWriter().write() similar （ stay tomcat Before the server actually responds to the client , Will look for response Buffer data , That is to say, execute first response.getWriter().write(), therefore response.getWriter().write() It will disrupt the order of code execution , Recommended out.write()）

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
   <head>
      <title>#[[$Title$]]#</title>
   </head>
   <body>
		  <%
				System.out.println("hello jsp");
				int i=5;
				String contextPath=request.getContextPath();
				out.print(contextPath);
			%>
		
			<%!
				int i=3;
			%>
			
			<%= "hello" %>
			
			<h1>hi~ jsp!</h1>
		
			<% response.getWriter().write("response");%>
   </body>
</html>

Four 、Session

1. Concept

Concept ： Server side session technology , Save the data to the server , Sharing data among multiple requests in a session , Save the data in the object on the server side ,HttpSession

2. Quick start

Quick start （ Use steps ）：

obtain HttpSession object ：
HttpSession session=request.getSession();
Use HttpSession object ：
Object getAttribute(String name);
void setAttribute(String name,Object value);
void removeAttribute(String name);

Set up Session
Insert picture description here obtain Session

3. Session Principle

1、Session rely on Cookie, When you first get session Object time , because Cookie Not carrying SessionID, Therefore, it cannot be found in the server memory session object , So it needs to be built session object .
2、 After new construction , hold sessionID Deposit in Cookie in , Respond to the browser , The next time the browser requests the server, it will use Cookie carry SessionID
3、 Server received SessionID after , When calling request.getSession() when , Will go to the memory to find the session object , Therefore, the object obtained at this time is the same as that in the first step session Object is the same
Insert picture description here

4. Session The details of the

4.1 When the client is shut down , The server does not shut down , Get twice Session Is it the same

By default , Not the same . because SessionID It's dependence Cookie Carry the , By default , When the browser closes ,Cookie It will clear away
If you need the same , You can manually create Cookie, The key is JSESSIONID, Set the maximum lifetime , Give Way Cookie Persistent save . The default is , automatically Cookie That is the first case

Cookie c=new Cookie("JSESSIONID",session.getId());
c.setMaxAge(60*60);
response.addCookie(c);

4.2 The client does not shut down , After the server is shut down , Get twice session Is it the same ？

Not the same . because session Objects are stored in server memory , When the server is down , Memory will be released naturally .

Solutions ：

session Passivation of ： Before the server is shut down properly , take session Serialize objects to hard disk
session Activation of ： After the server starts , take session The file is converted to... In memory session Object can

It should be noted that ： stay IDEA Can only achieve passivation , Activation cannot be achieved , Because it will be deleted in the middle work Folder , Rebuild again , The passivated persistent file is missing .tomcat The server can

4.3 session When it was destroyed

Server down
session Object call invalidate()
session Default expiration time 30min
Select configuration modification

<session-config>
	<session-timeout>30</session-timeout>
</session-config>

4.4 session Characteristics

Session Data used to store multiple requests for a session , There is a server side
Session Can store any type , Data of any size

4.5 Session and cookie The difference between

Session Store data on the server side ,Cookie On the client side
Session There is no data size limit ,Cookie Yes
Session Data security ,Cookie Relatively unsafe

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https://yzsam.com/2022/210/202207290121504196.html

当前位置：网站首页>Cookies and sessions

Cookies and sessions

Cookie and Session

One 、 Conversational Technology

Two 、Cookie

1. Concept

2. Quick start

3. Cookie The details of the

3.1 Can I send more than one at a time Cookie？

3.2 Cookie How long to save in the browser

3、 ... and 、JSP Introduction learning

1. Concept

2. Use

Four 、Session

1. Concept

2. Quick start

3. Session Principle

4. Session The details of the

4.1 When the client is shut down , The server does not shut down , Get twice Session Is it the same

4.2 The client does not shut down , After the server is shut down , Get twice session Is it the same ？

4.3 session When it was destroyed

4.4 session Characteristics

4.5 Session and cookie The difference between

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