2021-02-18-session introduction and the difference between session and cookie

concept

• Chinese translated into conversational meaning
• The bottom layer is based on cookies
• Key-value pair form
• It can be used to store the value that the backend wants to store, and then it can be obtained on the front-end page
• The default timeout time of the session is 30 minutes, and the default timeout time can be modified in the web.xml of the project

method

Method name	effect
getId()	Get SessionID
getCreationTime()	Get the creation time of the session
getLastAccessedTime()	Get the last operation time of the session
isNew()	Determine whether to obtain a new session (new user)
invalidate()	Invalidate the session
setAttribute(String s, Object obj)	Add content
getAttribute(String s)	Get content by key

The difference between session and cookie

Compared	cookie	session
Storage location	Client browser or hard drive	Server
Storage data type	A cookie can only store one key-value value, and both are of string type	Can save any type
Whether the client can operate	Can be accessed through js on the html side of the browser	Can't operate
Whether the server is operating	Can operate	Can operate
Create method	Cookie(String name, String value)	setAttribute(String s, Object obj)
Quantity stored	Generally, a project can have up to 20	There is only one shared session for a single client
Disadvantage	The client cannot write in if the cookie is disabled on the client. It is not safe to put data on the client.	Occupy server resources, so there is less data in the session

Domain object (four attribute ranges)

• appliaction: save on the server, all users can use
• pageContext: only saved in one page, invalid after jump
• request: only saved in one request, it is still valid after the server jumps
• session: Save in a session, you can use it regardless of any jump, but you can't use it after opening a new browser