JavaServer Pages (JSPs) - An Introduction to Network Programming with Java - page 273

Table 9.1 The implicit JSP objects

Variable Type Purpose

request HttpServletRequest Http request originally sent to server

response HttpServletResponse Http response to request

session HttpSession Session object associated with the

above request and response

application ServletContext Holds references to other objects that

more than one user may access,
such as a database link

out JspWriter Object that writes to the response

output stream

exception Throwable Contains information about a runtime

error and is available only on
error pages

pageContext PageContext Encapsulates the page context

confi g ServletConfi g ServletConfi g object for this JSP

page Object The this object reference in this JSP

ServletContext is an interface implemented by each servlet engine that provides
a servlet with methods that allow it to fi nd out about its environment (independent
of any individual session). This interface has two methods that mirror the Session
class's methods getAttribute and setAttribute . The two methods have names, argu-
ments and return types that are identical to those of the corresponding Session meth-
ods. The signatures for these methods are repeated below.

￿ public Object getAttribute(String <name>)
￿ public void setAttribute(String <name>,
Object <attribute>)
As shown in Table 9.1 , the implicit object application is the ServletContext
object that is created automatically for a JSP and allows the programmer to retrieve
and set environment-level properties via the two methods above.
In the examples below, note the need for typecasting with getAttribute , since it
returns an Object reference.

Examples

String userName =
(String)application.getAttribute("name");
Float balanceObject =
(Float)application.getAttribute("balance");
setAttribute("total", new Integer(0));
Other methods of object application that are sometimes useful are listed below
and have purposes that are self-evident.