Java Reference
In-Depth Information
Figure 21.4 shows the output of
time.jsp
.
FIGURE 21.4
Using an expres-
sion in a JSP
page.
When a page includes an expression, it's evaluated to produce a value and displayed on
the page. If the expression produces different values each time the page is displayed, as
time.jsp
does in line 7 of Listing 21.4, this is reflected in the page when loaded in a
web browser.
There are several servlet objects you can refer to in expressions and other elements of a
JSP page using the following variable names:
out
—The servlet output stream
n
request
—The HTTP servlet request
n
response
—The HTTP servlet responses
n
session
—The current HTTP session
n
application
—The servlet context used to communicate with the web server
n
config
—The servlet configuration object used to see how the servlet was initial-
ized
n
Using these variables, you can call the same methods from within a page that are avail-
able in a servlet.
Listing 21.5 contains the text of the next page you'll create,
environment.jsp
,
which shows how the
request
variable can be used on a page. This variable
represents an object of the
HttpServletRequest
class, and you can call the object's
getHeader(
String
)
method to retrieve HTTP headers that describe the request in more
detail.
21
LISTING 21.5
The Full Text of
environment.jsp
1: <html>
2: <head>
3: <title>Environment Variables</title>
4: </head>