What are the built-in objects of jsp?

jsp built-in objects are a set of objects created by the Web container. They can be used directly in JSP page scripts (Java program slices and Java expressions) without declaration or creation. variable.

Commonly used JSP built-in objects:

1, out object

buffer Area - Buffer is an area of ​​memory used to store temporary data.

The out object is an instance of the JSPWriter class, an object commonly used when outputting content to the client.

2. Request object

The client's request information is encapsulated in the request object, through which we can understand the customer's needs and then respond.

The request object is an instance of the HttpServletRequest class.

The request object has a request field, that is, the object is valid until the client's request is completed.

3. response object

The response object contains relevant information in response to customer requests. It is rarely used directly in JSP.

The response object is an instance of the HttpServletResponse class.

The response object has page scope, that is, when a page is accessed, the response object in the page can only be valid for this visit, and the response objects of other pages are invalid for the current page.

4. Session object

session: a session between the client and the server

Session in Web: The user is in When browsing a website, the time elapses from entering the website to closing the browser, that is, the time the user spends browsing the website.

session is actually a specific time concept.

The session object is automatically created when the first JSP page is loaded, and session management begins.

A session: starts when the client opens the browser and connects to the server, and ends when the client closes the browser and leaves the server.

session object is an instance of the HttpSession class.

5. Application object

The application object realizes data sharing between users and can store global variables;

application object, start Started when the server is started and terminated when the server is shut down;

In the user's previous and subsequent connections or connections between different users, the same property of the application object can be operated;

The application can be operated anywhere Operations on object attributes will affect other users' access to it;

The application object is an instance of the ServletContext class.

6. Page object

The page object refers to the current JSP page itself, a bit like the this pointer in the class;

The page object is Instance of java.lang.Object class.

7. pageContext object

pageContext object provides access to all objects and namespaces in the JSP page;

pageContext object , you can access the session where this page is located, and you can also get a certain attribute value of the application where this page is located;

The pageContext object is an instance of the pageContext class.

8. config object

The config object is used by the jsp engine to transfer information to a servlet when it is initialized. This information includes when the servlet is initialized. The parameters to be used (consisting of attribute names and attribute values) and server-related information (passing a ServletContext object);

#9, exception object

The exception object is an exception object. When an exception occurs during the running of a page, this object is generated. If a Jsp page wants to use this object, it must set isErrorPage to true, otherwise it cannot be compiled. Is an object of java.lang.Throwable.

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