Building Web Applications Using Servlets and JSP - Learn Java for Web Development - page 79

Table 2-4. Scope Objects

Scope Objects Servlet API Accessible From . . .

javax.servlet.ServletContext Application/web

context

Web components across the application

Subtype of javax.servlet.ServletRequest Request Web components that handle the request

javax.servlet.http.HttpSession

Session Web components in a session

javax.servlet.jsp.JspContext Page The JSP page that creates the object

Note In addition to the standard servlet request, session, and application scopes, JSP adds a fourth scope
called page scope .

A JSP page can access some specific objects through scripting variables. These objects are
provided by the JSP container and are called implicit objects . These implicit objects can be
accessed in scriptlets, in expressions, or as part of the EL expressions. (The EL expressions are
introduced in Chapter 3.) Table 2-5 lists the nine implicit objects with the corresponding API.

Table 2-5. Implicit Objects

Implicit Object Usage API

application ServletContext

Accesses application-level objects

config ServletConfig Provides configuration information

exception JSPException Accesses error status

out JSPWriter

Accesses the JSP output stream

page Object Provides a reference to the current JSP

pageContext PageContext

Accesses the JSP container

request ServletRequest Provides access to the client request

response ServletResponse Provides access to the JSP response

session HttpSession

Shares information across client requests

These implicit objects are described in more detail in the following sections.

application
The implicit application object provides a reference to the javax.servlet.ServletContext interface.
The ServletContext interface is used to provide access to any context-initialization parameters that
have been configured for the JSP page via the deployment descriptor of the web application. The
ServletContext object and parameters stored in them by the web container are available to the
entire web application. The application object provides the developer of the JSP page with access
to the ServletContext object.