5 JSTL Core IF Tag Examples in JSP - Tutorial

 or if tag of JSTL core tag library in JSP is
one of the most versatile and useful tag. JSTL if tag allows you

to test for a condition, like checking for a particular parameter in requestScope, sessionScope or pageScope. You can
also  check any parameter in request parameters and headers or can check for a variable in JSP
page using tag. JSTL if tag helps a
lot to reduce amount of Java code from JSP  page and if used, along with expression language JSTL core tag library, can remove almost all Java code from JSP files.
Earlier we have seen examples of JSTL foreach tag and JSTL core set tag and this JSP
JSTL tutorial is based on if tag of JSTL core tag library. We will, see how to
use tag inside JSP files and different example of
tag to get ourselves familiar with functionality and power offered by JSTL
tag. After seeing these examples of
tag along with expression language, You will be amazed to see, how clean your
JSP looks like.

What is tag in JSTL and JSP

or tag, based
on prefix you choose on taglib declaration, is part of
standard JSTL (Java Standard Tag libary). JSTL
tag test one condition and display or evaluate body content only if
condition is true. If test expression results in false than content of
body is not evaluated. Here is syntax of JSTL if tag:

<core:if test="boolean
expression" var="variable" scope="scope">

body content only be evaluated if test condition will be true

core:if>

test attribute contains a boolean expression which
is used to test a condition while attribute var and scope can be
used to store the result of test into a particular variable
specified by var and in a particular scope specified by scope.
We will see example of JSTL if tag for storing test result in example section.

How to
use JSTL IF tag in JSP

Here is a step by step guide to use JSTL
tag inside JSP file:

1) Download Java standard tag library or if you are using Maven along
with Eclipse or Netbeans IDE then just import

dependency. Netbeans itself maintains set of libraries including JSTL, Spring and Struts, if you download there web package.

2) Include jstl.jar in application’s classpath.
In web application, you should put JAR
files on WEB-INF/lib folder, that folder is available
on web application’s classpath.

3) Import JSTL core tag library in your JSP file by using tag

<%@ taglib prefix="core"
uri="http://java.sun.com/jsp/jstl/core" %>

Now you are ready to use JSTL if tag in your JSP  file , just follow sytax of
tag and you will be fine. Here prefix core will be used along with IF tag
e.g. .

JSTL
if tag Examples in JSP

Here are some frequently used examples of tag for
checking request parameters, header values in JSP pages. This examples can be
best used to remember syntax of JSTL if tag.

1) If condition with request parameter in JSP

<core:if test="${param.loan !=
null}">

How to get: <%=request.getParameter("loan")%>

core:if>

This block of code in JSP will only execute, if request contains a
parameter called loan and will not display anything if request
parameter doesn't contain any parameter named loan.

2) If condition with header parameter in JSP

This is similar to above example of JSTL if tag. Only difference is,
instead of request parameters now will check
headers for a particular parameter as shown in below code:

<core:if test="${header.cookie
== null}">

Hello: ${header.cookie}

core:if>

This JSTL example checks if cookie is present in HTTP header and display
value of cookie if present.

3) How to check a particular variable in pageScope, requestScope and sessionScope in JSTL if
tag.

In this JSTL If tag example, we
have put a variable loan in request scope using <c:set> tag, which is another
JSTL tag. Later we check for same variable using tag.

<c:set var="loan" value="Property
Loan" scope="request" />

<c:if test="${requestScope.loan
!= null }">

Loan type is ${requestScope.loan}

c:if>

4) How to check for a bean value in JSP if tag

This if tag will only be executed if type property of loan object is "Personal
Loan". This way you can check for any property of bean for particular value or
null.

<c:if test="${loan.type == 'Personal
Loan'}">

${loan}<br>

c:if>

5) How to show  result of tag test
in JSP

You can export result of tag
condition check using var and scope. var is used to define name of variable
which holds result of if tag evaluation and scope define scope of that
variable. In following example, variable cookieTestResult will hold
result of if tag evaluation in request scope.

<c:if test="${header.cookie
== null}" var="cookieTestResult" scope="request">

Hello: ${header.cookie}

c:if>

Result of Cookie Test:  <c:out
value="${requestScope.cookieTestResult}"/>

Important
points on JSTL tag

Now we know How to use JSTL tag, let’ revise some
important things about this tag in JSP.

1) While using if tag from JSTL core library along with expression
language its good to recap implicit variables available to Expression Language
or EL in JSP. They are pageContext, pageScope, requestScope, sessionScope and applcationScope. They are
self explanatory and represent Map holding request, session or application
level attributes key is the name of attribute and value form Map is value of
that attribute. Apart from these 5 we have 6 more maps called param, paramValues, header, headerValues, cookie and initParam. As name
suggest they hold request and header parameters, name and values of cookie and
init parameters.

2)  Also remember about dot(.)
and bracket([]) operator in JSP expression language;
dot is used to get property from object and bracket is used to get elements
from collections and arrays.

That’s all on How to use or JSTL If
tag in JSP pages. For Java programmers, who sometime has added responsibility
to code JSP as well, it’s difficult to remember syntax and options of various
JSTL tags. These tag example will help to
quickly remember how to use JSTL if tag with full of its potential.

Source:http://javarevisited.blogspot.com/2013/02/5-jstl-core-if-tag-examples-in-jsp.html