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Expression Language
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Overview Expression Language EL Features Variable / Attribute Implicit Objects
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Script Expression
Any required value can be directly placed into the generated dynamic content using JSP expression
The expression is inserted into the JSP page after being evaluated and converted to string
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Expression Language New feature of JSP 2.0 Allows JSP developers to access java
objects via a compact, easy-to-use shorthand style
Developed by two groups– JSP Standard Tag Library expert group – JSP 2.0 expert group
Syntax– ${EL Expression}
JSP EL expressions are used in– Static text– Standard and Custom tags
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EL Features Key Features
– Easy syntax for accessing variables– Special support for collection objects and arrays– Implicit objects– Arithmetic
EL expressions can be disabled / enabled using isELIgnored attribute– <%@page isELIgnored=“true | false” %>
JSP EL Expressions are evaluated at runtime
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EL Expression with Prior JSP 2.0
By default JSP 1.2 or prior version ignore the EL Expression
<?xml version="1.0" encoding="UTF-8"?><web-app version="2.4" xmlns="http://java.sun.com/xml/ns/j2ee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd"><jsp-config>
<jsp-property-group><url-pattern>*.jsp</url-pattern><el-ignored>false</el-ignored>
</jsp-property-group></jsp-config>
</web-app>
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Variable / Attribute Variables are used to store and access
values in JSP program Variable refers as a attributes that are
stored in standard scope such as page, request, session and application
Dot operator . or square brackets [ ] can be used to access value of variable– ${pageScope.color}– ${pageScope[“color”]}
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EL - Implicit Objects
Implicit Objects
pageContext cookieinitParamparamValuesparam
header headerValues
application
servletContext
request
session
response
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EL Operators
*
/ or div
+
-
% or mod
Operators
EmptyLogicalRelationalArithmetic
< or lt
> or gt
< = or le
> = or ge
= = or eq
!= or ne
&& or and
|| or or
! or not
empty
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EL Arithmetic Operators
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EL Relational Operators
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EL Logical Operators
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EL Empty Operators
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Call static method using EL
Static methods can be called within the EL expression
Step to call static methods using EL– Define static method– Regist with tag libray descriptor– Access EL functions within JSP
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Define static method
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Register with tag library descriptorDeclare the static function with the .tld file
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Access EL functions within JSPAccess the function using an EL expression
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Coercion
Converts parameters to the appropriate objects or primitives automatically
JSTL defines appropriate conversion with default values
Coercion
Boxing and Unboxing
Coercion to String
Coercion to Number
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Summary
Expression Language– ${EL Expression}
EL Features Variable / Attribute Implicit Objects
