JSTL Core
Actions
The JSTL – Java Server Pages Standard
Tag Library is a collection of useful JSP tags which encapsulates
the core functionality common to many JSP applications. The JSTL is
divided into several separate functional areas, each with its own namespace as
shown in Table 1.
Table 1: JSTL Functional Areas
|
Functional area |
Namespace Name prefix |
Capabilities |
|
Core |
c |
basic operations such as variables declaration,
printing/displaying values, performing iterations, declaring conditional statements,
etc |
|
XML Processing |
xml |
allows a range of XML-related functions to be performed by a JSP document,
including XSLT processing. |
|
Functions |
fn |
Provides 1.
a length() function that can be used to obtain
the number of elements in a collection 2.
a variety of standard string processing functions that can be included
in EL expressions. |
|
Database |
sql |
allows a JSP document to directly access a
database rather than accessing it indirectly through JavaBeans objects |
|
Internationalization |
fmt |
allows strings representing data such as currency
or dates to be formatted appropriately for a given locale |
The basic features of the JSTL core actions are
|
Action |
Purpose |
|
set |
Assign a value to a scoped variable, creating the
variable if necessary |
|
remove |
Destroy a scoped variable |
|
out |
Write data to out implicit object, escaping XML
special characters |
|
url |
Create a URL with query string |
|
if |
Conditional (if-then) processing |
|
Choose |
Conditional (if-then-elseif)
processing |
|
forEach |
Iterate over a collection of items |
Naming conventions
When the attribute var is specified in a JSTL element, it represents the name
of a scoped variable that is being assigned a value by the element. The scope
attribute is set to one of four values – page (default), request, session, or
application. The values of var and scope attributes
must be string literals.
<c:set
var="visits" scope="application"
value="${visits+1}" />
Example
program to demonstrate JSTL Core actions
<!-- JSTL Core actions -->
<%@ taglib uri = "http://java.sun.com/jsp/jstl/core" prefix="c" %>
<html>
<body>
<h2>JSTL
Core Actions </h2>
<h3>
var, scope, set and out ...
<c:set
var = "sal"
scope="session" value="${2000}"/>
<c:out
value = "${sal}"/>
<c:set
var = "msg"
scope="page" value="${'hello'}"/>
<c:out
value = "${msg}"/>
remove ...
<c:remove
var = "sal"/>
value after removing an attribute = <c:out
value = "${sal}"/>
if ...
<c:if
test="${empty visits}">
<c:set var="visits"
scope="application" value="0" />
</c:if>
Hit count =
<c:set
var="visits" scope="application" value="${visits+1}"
/>
<c:out value =
"${visits}"/>
choose ...
<c:set
var = "Num" scope
= "session" value = "${0}"/>
<c:choose>
<c:when test="${Num < 0}">
${Num} is negetive.
</c:when>
<c:when test="${Num > 0}">
${Num} is positive.
</c:when>
<c:otherwise>
Zero.
</c:otherwise>
</c:choose>
forEach...
<c:forEach
var="i" begin="2"
end="20" step="2">
${i}
</c:forEach>
url ...
<a href =
"<c:url value =
"/hello.html"/>">TEST</a>
</h3>
</body>
</html>
Output:
JSTL Core Actions
var, scope, set and out ...
|
JSTL
Functions
|
Function |
Purpose |
|
fn:contains() |
checks whether the given string is present in the input as sub-string. It
does a case sensitive check |
|
case insensitive check to see whether the provided string is a sub-string
of input. |
|
|
To find the start position of a string in the
provided string. Function returns -1 if string is not found |
|
|
fn:join() |
concatenates the strings with a given separator and returns the output string. |
|
fn:split() |
splits a given string into an array of substrings. |
|
for computing the length of a string or to find out the number of
elements in a collection. It returns the length of the object |
|
|
checks the specified string is a prefix of given
string |
|
|
for checking the suffix of a strin |
|
|
for getting a substring from the provided string |
|
|
removes spaces from beginning and end of a string and function. |
|
|
converts input string to a uppercase string. |
|
|
converts input string to a lower case string |
|
|
to search for a string in the input and replace it with the provided
string. – case sensitive processing |
<!-- JSTL Functions -->
<%@ taglib uri =
"http://java.sun.com/jsp/jstl/core"
prefix="c" %>
<%@ taglib uri =
"http://java.sun.com/jsp/jstl/functions"
prefix="fn" %>
<html>
<body>
<h2>JSTL
Functions </h2>
<h3>
<c:set var = "msg" scope="page" value="${'Hello
World'}"/>
Original String = <c:out value = "${msg}"/>
Uppercase : ${fn:toUpperCase(msg)}
Lowercase : ${fn:toLowerCase(msg)}
Length : ${fn:length(msg)}
Substring : ${fn:substring(msg, 0, 5)}
Replace : ${fn:replace(msg,
"Hello", "Hai")}
</h3>
</body>
</html>
Output:
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