EL Implicit Objects
EL is the JSP 2.0 Expression Language Interpreter from Apache Corporation. EL means the expression language , it makes it possible
to easily access application data stored in JavaBeans components. The jsp
expression language allows a page author to access a bean using simple syntax
such as $(name). Before JSP 2.0, we could use only a scriptlet,
JSP expression, or a custom tag to include server state in the jsp page output.
Expression Language (EL) was first introduced in JSTL 1.0. EL makes it easier to
integrate server side state with the presentation output.
EL expression is always written between the delimiters
${ and }. In the JSP page response, the result of expression evaluation replaces
the expression and its delimiters in the template text. Within tags, expression
can be used only in attribute values.
The JSP expression language defines various implicit
objects:
- pageContext: The context for the JSP page. It
contains the reference of the following objects.
- servletContext
- session
- request
- response
2. param: It maps a request parameter name to a
single value.
3. paramValues: It maps a request parameter name
to an array of values.
4. header: It maps a request header.
5. cookie: It maps a cookie name to a single
cookie.
6. initParam: It maps the context initialization
parameter name.
The code of the program is given below:
<html>
<head>
<title>JSP 2.0 Expression Language
- Implicit Objects</title>
</head>
<body>
<h6>JSP 2.0 Expression Language - Implicit Objects</h6>
The list of the implicit objects available
in the Expression Lanaguage.
Not available are illustrated here:
<ul>
<li>pageContext - the PageContext object</li>
<li>requestScope
- a Map that maps request-scoped attribute names
to their values</li>
<li>sessionScope
- a Map that maps session-scoped attribute names
to their values</li>
<li>applicationScope
- a Map that maps application-scoped attribute
names to their values</li>
<li>param
- a Map that maps parameter names to a single String
parameter value</li>
<li>paramValues
- a Map that maps parameter names to a String[] of
all values for that parameter</li>
</ul>
<blockquote>
<br>
<code>
<table border="1">
<thead>
<td><b>EL Expression</b></td>
<td><b>Result</b></td>
</thead>
<tr>
<td>\${header["host"]}</td>
<td>${header["host"]}</td>
</tr>
<tr>
<td>\${header["accept"]}</td>
<td>${header["accept"]}</td>
</tr>
<tr>
<td>\${header["user-agent"]}</td>
<td>${header["user-agent"]}</td>
</tr>
</table>
</code>
</blockquote>
</body>
</html>
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The output of the program is given below:
Download
this example.
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