JSP built-in object, jsp built-in

JSP built-in object, jsp built-in

In JSP, nine built-in objects are provided to simplify user development. These built-in objects are instantiated by containers for users and can be directly used by users instead of in Java, you must use the new keyword to instantiate an object before using it.

Nine built-in objects in JSP

No.	Built-in object	Type	Description
1	PageContext	Javax. servlet. jsp. PageContext	JSP page container
2	Request	Javax. servlet. http. HttpServletRequest	Obtain user request information
3	Response	Javax. servlet. http. HttpServletResponse	Response Information from the server to the client
4	Session	Javax. servlet. http. HttpSession	Used to save information of each user
5	Application	Javax. servlet. ServletContext	Indicates the shared information of all users.
6	Config	Javax. servlet. ServletConfig	Server configuration to obtain initialization parameters
7	Out	Javax. servlet. jsp. JspWriter	Page output
8	Page	Java. lang. Object	Indicates a Servlet instance displayed from this page.
9	Exception	Java. lang. Throwable	Indicates the exception on the JSP page, which takes effect only on the error page.

Among the nine built-in objects above, pageContext, request, response, session, and application are commonly used.

The storage range of four attributes is provided in JSP. The attribute storage range refers to the number of pages on which a built-in object can be saved and used.

• Page: only save attributes on one page. It is invalid after redirect.
• Request: it is saved in only one request, and is still valid after server jump.
• Session: in the range of a session, no matter what type of Jump can be used, but the new browser cannot be used.
• Application: it is saved on the entire server and can be used by all users.