JSTL Functions with Examples

In this article, we will discuss all JSTL functions with examples. The JSTL library provides a number of standard functions. Most of these functions are common string manipulation functions. The syntax used for including the JSTL functions library in your JSP is as follows:

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

Introduction to JSTL Functions

JSTL (JavaServer Pages Standard Tag Library) functions are a set of functions provided to ease the development of JSP pages by enabling common operations without the need for scriptlets. These functions help in performing string manipulations, collection operations, and other basic tasks seamlessly within JSP pages.

List of JSTL Function Tags

Let's list all the JSTL functions and their meanings and examples.

1. fn:contains Function

This function checks whether the given string is present in the input as a substring. It does a case-sensitive check.

Syntax:

boolean fn:contains(String inputstring, String checkstring)

Example:

<h1>JSTL fn:contains() function example</h1>
<c:set var="str1" value="Java Guides" />
<c:set var="str2" value="Guides" />
<c:if test="${fn:contains(str1, str2)}">
  <c:out value="'Guides' substring present in 'Java Guides' string" />
</c:if>
<hr>

2. fn:containsIgnoreCase Function

It does a case-insensitive check to see whether the provided string is a substring of the input.

Syntax:

boolean fn:containsIgnoreCase(String input, String checkstring)

Example:

<h1>JSTL fn:containsIgnoreCase() function example</h1>
<c:set var="str1" value="Java Guides" />
<c:set var="str2" value="java guides" />
<c:if test="${fn:containsIgnoreCase(str1, str2)}">
  <c:out value="'java guides' substring present in 'Java Guides' string" />
</c:if>
<hr>

3. fn:indexOf Function

This JSTL function finds the start position of a string in the provided string. The function returns -1 when the string is not found in the input.

Syntax:

int fn:indexOf(String input, String searchString)

Example:

<h1>JSTL fn:indexOf() function example</h1>
<c:set var="str1" value="Java Guides" />
<c:set var="str2" value="Guides" />
<p>Index of "Guides" in "Java Guides": ${fn:indexOf(str1, str2)}</p>
<hr>

4. fn:escapeXML Function

This function is used for HTML/XML character escaping, which means it treats HTML/XML tags as a string. It is similar to the escapeXml attribute of the <c:out> tag.

Syntax:

String fn:escapeXml(String inputString)

Example:

Message1: <b>Hi This is just a message</b>
<br>Message2: <i>This is an example</i>
<br>Message1 and fn:escapeXml(): ${fn:escapeXml("<b>Hi This is just a message</b>")}
<br>Message2 and fn:escapeXml(): ${fn:escapeXml("<i>This is an example</i>")}
<hr>

5. fn:join and fn:split Functions

• 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 based on a delimiter.

Syntax for fn:join:

String fn:join(String arrayofstrings, String separator)

Example:

<h1>JSTL fn:join() function example</h1>
<%
String arr[] = { "Java", "Programming", "Language" };
session.setAttribute("names", arr);
%>
${fn:join(names, " & ")}
<hr>

Syntax for fn:split:

String[] fn:split(String inputString, String delimiterString)

Example:

<h1>JSTL fn:split() function example</h1>
<c:set var="msg" value="This is an example of JSTL function" />
<c:set var="arrayOfMsg" value="${fn:split(msg,' ')}" />
<c:forEach var="i" items="${arrayOfMsg}">
    arrayOfMsg[${i.index}]: ${i}<br>
</c:forEach>
<hr>

6. fn:length Function

The JSTL function fn:length() is used to compute the length of a string or to find out the number of elements in a collection. It returns the length of the object.

Syntax:

int fn:length(Object obj)

Example:

<h1>JSTL fn:length() function example</h1>
<c:set var="str" value="Java Guides" />
Length of str is: ${fn:length(str)}
<hr>

7. fn:startsWith Function

It checks if the specified string is a prefix of a given string.

Syntax:

boolean fn:startsWith(String input, String prefix)

Example:

<h1>JSTL fn:startsWith() function example</h1>
<c:set var="str" value="Java Guides" />
Java Guides starts with Java: ${fn:startsWith(str, 'Java')}
<hr>

8. fn:endsWith Function

The fn:endsWith() JSTL function is used for checking the suffix of a string. It checks whether the given string ends with a particular string.

Syntax:

boolean fn:endsWith(String inputString, String suffixString)

Example:

<h1>JSTL fn:endsWith() function example</h1>
<c:set var="str" value="Java Guides" />
Java Guides ends with Guides: ${fn:endsWith(str, 'Guides')}
<hr>

9. fn:substring Function

This JSTL function is used for getting a substring from the provided string.

Syntax:

String fn:substring(String inputString, int start, int end)

Example:

<h1>JSTL fn:substring() function example</h1>
<c:set var="str" value="Java Guides" />
${fn:substring(str, 5, 10)}
<hr>

10. fn:substringAfter Function

This method is used for getting a substring that is present in the input string before a specified string.

Syntax:

String fn:substringAfter(String inputString, String subString)

Example:

<h1>JSTL fn:substringAfter() function example</h1>
<c:set var="str" value="Java Guides" />
${fn:substringAfter(str, "Gu")}
<hr>

11. fn:substringBefore Function

This method gets a substring from the input, which comes after a specified string.

Syntax:

String fn:substringBefore(String inputString, String subString)

Example:

<h1>JSTL fn:substringBefore() function example</h1>
<c:set var="str" value="Java Guides" />
${fn:substringBefore(str, "Gu")}
<hr>

12. fn:trim Function

This fn:trim() function removes spaces from the beginning and end of a string.

Syntax:

String fn:trim(String input)

Example:

<h1>JSTL fn:trim() function example</h1>
<c:set var="str" value="  Java Guides  " />
Trim of " Java Guides " is: ${fn:trim(str)}
<hr>

13. fn:toUpperCase Function

It is the opposite of fn:toLowerCase() function. It converts the input string to an uppercase string.

Syntax:

String fn:toUpperCase(String input)

Example:

<h1>JSTL fn:toUpperCase() function example</h1>
<c:set var="str" value="java guides" />
Upper case of "java guides" is: ${fn:toUpperCase(str)}
<hr>

14. fn:toLowerCase Function

This function is used for converting an input string to a lower case string.

Syntax:

String fn:toLowerCase(String input)

Example:

<h1>JSTL fn:toLowerCase() function example</h1>
<c:set var="str" value="JAVA GUIDES" />
Lower case of "JAVA GUIDES" is: ${fn:toLowerCase(str)}
<hr>

15. fn:replace Function

This fn:replace() function searches for a string in the input and replaces it with the provided string. It performs

case-sensitive processing.

Syntax:

String fn:replace(String input, String searchFor, String replaceWith)

Example:

<c:set var="author" value="Ramesh Fadatare" />
<c:set var="randomString" value="abc def abc ghi ABC" />
${fn:replace(author, "Ramesh", "Umesh")} 
${fn:replace(randomString, "abc", "hello")}
<hr>

Conclusion

JSTL functions are a powerful feature in JSP that simplify common tasks such as string manipulation, collection handling, and HTML/XML escaping. By using these functions, developers can write cleaner, more readable, and maintainable JSP pages. This guide has covered the most commonly used JSTL functions along with examples to help you understand how to use them effectively in your web applications.