The three domain objects of Servlet

Three commonly used domain objects in Servlet

Object type	Object name
HttpServletRequest	request
HttpSession	session
ServletContext	application

request domain

Create: The client sends a request to the server, and the server creates a request object.
Destruction: The server will destroy the request object after responding to this request
. Scope: only valid in the current request

session domain

Creation: the first time the server calls getSession(); the session domain is created and saved in the server memory for
destruction:

1. Abnormally shut down the server (normally shut down the session will be serialized, restart the server session will be deserialized)
2. The session expired by default 30 minutes
3. Manually call session.invalidate();
   Note: If you close the browser and visit again, you will not find the session id of the session instead of the session being destroyed

Scope: Open the browser session to start, close the browser session to end. Valid throughout the session

application domain

Creation: The server creates an object ServletContext class belonging to the web application for each WEB application when the server starts.
Destruction: The server is closed or the project is removed from the server.
Scope: It is valid on the entire server.