cookie and session

javaweb And :Cookie Mechanism

1. Study Cookie and Session Why ?

1.Http The agreement itself is stateless , namely   No status information will be saved between multiple requests . But in actual development , Many times, you need to pass information between multiple requests . You need to learn the technology of maintaining conversation .cookie and session Are used to maintain conversation Technology .

2.Cookie Mechanism ?

javax.servlet.http.Cookie: class   The only one JAVAWEB We can new
1.Cookie: Cookies , Little cookie . It is a small amount of string information passed by the server to the client . Save in the client browser ( Memory / Hard disk ),  When you access the server again later , hold Cookie The information is sent back to the server .
Cookie Only text messages .  No more than 4K

2. How to send cookie:[Server--->Client]
	1.Cookie Information through  response.addCookie(new Cookie(key,value)), The bottom layer of this method is by adding HTTP Respond to the header in a way that cookie Information is transmitted from the server to the client .
	
3. How to return cookie:[Client===>Server]
	 When accessing the server again ,Cookie Save information to HTTP Request header , Send back to the server . We're on the server （Servlet/Controller etc. .） adopt request.getCookies() Get the last server sent client carried by this request Cookie Information .
	
4.Cookie Is the only one we can new The object of , We must new, You can set the expiration time setMaxAge( Seconds per unit ), If not set  maxage, Is saved in memory .

3. Case study :

1. Remember me   Remember the user name 

2. Last visit 

3. Recently viewed products  

Session Mechanism

1.Session The principle of mechanism

0.session To express a conversation . In general, a session contains multiple requests .

1.Session The core of the mechanism API:javax.servlet.http.HttpSession Interface 

2. When the client accesses the server for the first time , And the server executes request.getSession() When the method is used , The server will create a HttpSession Object of type , Then assign a unique identifier to the object sessionid. With cookie In the form of sessionid Back to the client browser . Save to browser memory .
setAttribute(key,value); Sign in ==session.setAttribute("user",user)
 Memory shopping cart  

3. When you access the server again ,sessionid With cookie Is returned to the server . Server according to sessionid, Find... In memory session object , Get content .

2.session Session failure of ?

1.session There is a default effective time  , Default 1800 second .

2.invalidate  Method is called .session Lapse immediately  ==》 Cancellation / sign out 

3. Close the browser . Browser closed ---》 Memory free --》sessionid be without --》 The server cannot be based on sessionid Find the original session Object , Only new .

3. Session What data is generally stored in ？

1. Data needed for a page ：request:setAttribute/getAttribute()

2. Data to be displayed on multiple pages :session：setAttribute()/getAttribute()

3. Data shared by all :application==ServletContex:setAttribute()/getAttribute()

 Domain   Range 

3.Cookie and Session The difference between ？

1.Cookie The object of   Program ape itself new,Session object   Server construction .

2.Cookie The information is stored in the client browser .Session Objects are stored in server memory .

 contact :session In the process of mechanism implementation , Using the cookie,sessionid