jsp nine built-in objects in the object and effect of the four domains

Copyright: https://blog.csdn.net/No_mingzi/article/details/90604674

pageContext current jsp page
request within a request (request forwarding)
the session with a session (open a browser to access the server, then there will be a session until the browser is closed, it lost contact session.)
the Application when the entire web project (web project launched Creating ServletContext, time to stop the destruction of ServletContext)

Four domains from small to large are: pageContext -> request -> Session -> application

Four domain when using the priority order is from small to large, the reason is to try to free up memory.