4. Nine built-in objects of jsp
request request object
response object
pageContext jsp context object
session object
application ServletContext object
config ServletConfig object
out jsp output stream object
page points to the current jsp object
exception exception object
Among them, pageContext, request, session, and application are the four domain objects
What is a domain object? Objects that can access data like Map.
Order of use: Start pageContext–request–session–application from a small scope
range
pageContext (PageContextImpl class) is valid in the current jsp page
request (HttpServletRequest class) valid within one request
session (httpSession class) is valid within the scope of a session (open the browser and know that it is closed is a session)
application (ServletContext class) As long as the web project does not stop, the entire web project is valid