♠ Posted by Unknown in Adv Java at 08:15
JSP Scripting Elements
Once the directives have been used to
setup the scripting environment you can utilize the scripting language
elements. JSP1.1. has three scripting language elements – declaration,
scriptlets, and expressions. A declaration will declare elements, a scriptlet
is a statement fragment, and an expression is a complete language expression.
In JSP each scripting element begins with a “<%”.
The syntax for each is:
<%! Declration %>
<% scriptlet %>
<%= expression %>
White space is optional after “<%!”,
“<%”, “<%=”, and before “%>”. All these tags are based upon XML, you
could even say that a JSP page can be mapped to a XML document. The XML
equivalent syntax for the scripting elements above would be:
<jsp:declaration> declaration
</jsp:declaration>
<jsp:scriptlet> scriptlet
</jsp:scriptlet>
<jsp:expression> expression
</jsp:expression>
In addition, there are two types of
comments:
<%-- jsp comment --%>
<!-- html comment -->
The first form allows you to add comments
to JSP source pages that will not appear in any form in the HTML that is sent
to the client. Of course, the second form of comment is not specific to JSPs –
it’s just an ordinary HTML comment. What’s interesting is that you can insert
JSP code inside an HTML comment and the comment will be produced in the
resulting page, including the result form the JSP code.
Declarations are used to declare
variables and methods in the scripting language (Currently Java only) used in a
JSP page. The declaration must be a complete Java statement and cannot produce
any output in the out stream.
Example of JSP
<%--
Write a JSP program to implement the concept of scripting.
<%-- Below is a JSP Directive --%>
<%@ page import =
"java.util.*" %>
<%-- Below are declarations: --%>
<%!
long
loadTime = System.currentTimeMillis();
Date
loadDate = new Date();
int
hitCount = 0;
%>
<HTML>
<BODY>
<H1>This
page was loaded at <%= loadDate %> </H1>
<H1>Hello,
world! it's <%= new Date() %> </H1>
<H2>Here's
an object : <%= new Object() %> </H2>
<H2>This
page has been up <%= (System.currentTimeMillis() - loadTime)/1000 %>
seconds</H2>
<H3>
Page has been accessed <%= ++hitCount %> times since M%= loadDate %>
</H3>
<%
System.out.println("Good
Bye");
out.println("Good
Night");
%>
</BODY>
</HTML>
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