What is the built-in objects?
Jsp development in some frequently used objects, such as ServletContext, HttpSession, PageContext the like;
If every time we need to use these objects in jsp page should create their own hands would be particularly cumbersome.
SUN company when designing jsp, jsp after page load will be created these objects, you only need to use the corresponding object can call the appropriate methods .
The system creates an object called a good built-in objects .
In the servlet program, if the developer wishes to use the session object, the object must be obtained by Request.getSession session ();
In jsp program, developers can directly use the session (system to help us create good session object name is called session) can call the appropriate method.
Nine built-in objects :
Built-in objects Category :
● input and output objects: out objects, response objects, request the object
● communication control objects: pageContext objects, session objects, application objects
● Servlet objects: page objects, config objects
● Error Handling objects: exception Object
The role of built-in objects:
| Objects | effect |
| request | It encapsulates a variety of information from the client, the browser |
| response | It encapsulates the corresponding information server |
| out | For the client, the browser output data |
| session | Used to store session information. I.e., data can be shared between different requests from the same user |
| application | It represents the context of the current application. Information can be shared between different users |
| config | Configuration information of the application wrapper class |
| pageContext | JSP page provides access to all the objects and namespaces |
| page | Pointing to the current JSP program itself |
| exception | Encapsulates the information and exception error occurred during execution of the program JSP |
Built-in objects parse : ← Click
Four domain object
Domain Category :
● ServletContext 域
● HttpServletRequest 域
● HttpSession domain - the first three in the study will be able to come into contact with Servlet
● PageContext domain - JSP Learning
The role of domain objects : save data, access to data, data sharing
Save data :
. pageContext setAttribute ( "Content"); // default saved to the page domain
pageContext. setAttribute ( "Content", domain-wide constant); // save to the specified domain
Four constant domains :
- PageContext.PAGE_SCOPE
- PageContext.REQUEST_SCOPE
- PageContext.SESSION_SCOPE
- PageContext.APPLICATION_SCOPE
Get Data :
. the pageContext the getAttribute ( "content");
. the pageContext the getAttribute ( "name", the range of the constant domain);
Automatic four in the search field data pageContext findAttribute ( "Content");
Four automatic search data field, the order of : Page Domain -> request Domain -> session Domain -> application domain (context domain)
Domain scope
● page domain; only in the current jsp page use (current page)
● request field; the same can only be used in a request (forward)
● session domain; can only be used in the same session (session object) in the (private)
● context domain; use only (global) in the same web application