A First
JavaServer Page Example
We begin our introduction to JavaServer Pages with a simple example
(Fig. 31.1) in which the current date and time are inserted into a Web page
using a JSP expression.
<?xml version = "1.0"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0
Strict//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<!-- Fig. 10.1: clock.jsp -->
<html xmlns = "http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv = "refresh" content = "60" />
<title>A
Simple JSP Example</title>
<style type = "text/css">
.big { font-family: helvetica, arial,
sans-serif;
font-weight: bold;
font-size: 2em; }
</style>
</head>
<body>
<p class = "big">Simple
JSP Example</p>
<table style = "border: 6px
outset;">
<tr>
<td style = "background-color:
black;">
<p class = "big" style =
"color: cyan;">
<!-- JSP expression to insert date/time
-->
<%= new java.util.Date() %>
</p>
</td>
</tr>
</table>
</body>
</html>
Fig. 31.1 Using a JSP expression to insert
the date and time into a Web page
As you can see, most of clock.jsp consists of XHTML markup. In cases like this, JSPs are easier to
implement than servlets. In a servlet that performs the same task as this JSP,
each line of XHTML markup typically is a separate Java statement that outputs
the string representing the markup as part of the response to the client.
Writing code to output markup can often lead to errors. Most JSP editors
provide syntax coloring to help program-mers check that their markup follows
proper syntax.
The JSP of Fig. 31.1 generates an XHTML document that
displays the current date and time. The key line in this JSP (line 30) is the
expression
<%=
new java.util.Date() %>
JSP expressions are delimited by <%= and %>. This
particular expression creates a new in-stance of class Date from
package java.util. When the client requests this JSP, the preceding expression inserts
the String representation of the date and time in the re-sponse to the client.
Note that we use the XHTML meta element on line 10 to set a refresh interval of 60 seconds for the
document. This causes the browser to request clock.jsp every 60
sec-onds. For each request to clock.jsp, the JSP container reevaluates the expression on line 30, creating a
new Date object with the server’s current date and time.
As in Chapter 30, we use Apache Tomcat to test our
JSPs in the advjhtp1 Web application we created previously. For details on creating and
configuring the advjhtp1 Web application, review Section 30.3.1 and Section 30.3.2. To test clock.jsp, create
a new directory called jsp in the advjhtp1 subdirectory of Tomcat’s webapps directory. Next, copy clock.jsp into the jsp directory. Open your Web browser and enter the fol-lowing URL to test clock.jsp:
http://localhost:8080/advjhtp1/jsp/clock.jsp
When you first invoke the JSP, notice the delay as Tomcat translates the JSP into a servlet and invokes the servlet to respond to your request. [Note: It is not necessary to create a di-rectory named jsp in a Web application. We use this directory to separate the examples in this chapter from the servlet examples in Chapter 30.]
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