JSTL fn:substring() Function

Last Updated : 23 Jul, 2025

In JSTL, the fn:substring() function is used to extract or retrieve the part of a given input or specified string, by starting from the start index to the end index [optional]. This function is mainly used for string manipulation tasks by many developers.

In this article we will explore the Syntax along with the Parameters of the JSTL fn:substring() function, also we will see the practical implementation of this function in terms of examples.

Syntax of JSTL fn:substring() Function

${fn:substring(string, startIndex ,endIndex)}

Where,

  • string: input string from which the part of the substring will be extracted.
  • startIndex: initial position or the starting index (inclusive) for the substring. This means that the extracting will start from this index.
  • endIndex: ending index (exclusive) which is optional for the substring.

Note: If this index is not included, then the substring continues to the end of the input string

Example of fn:substring()

In this example, we will discuss the use of fn:substring(), to generate different substrings.

HTML 
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<%@ taglib uri="http://www.oracle.com/technetwork/java/index.html prefix="c" %>
<%@ taglib uri="http://www.oracle.com/technetwork/java/index.html prefix="fn" %>
  
<html>
  <head>
      <title>JSTL fn:substring() Example</title>
  </head>
  <body>
    <c:set var="mainString" value="GeeksforGeeks"/>
    <h3>Main String: ${mainString}</h3>
    
    <p>Substring from index 5 to the end: ${fn:substring(mainString, 5)}</p>
    <p>Substring from index 0 to 5: ${fn:substring(mainString, 0, 5)}</p>
 
  </body>
</html>

Output:

Output Screen of JSTL fn:substring() Function Program
Output

Explanation of the above Program:

  • mainString is initialized with the value "GeeksforGeeks".
  • The first <p> tag mainly extracts the substring from index 5 to the end of the main string, result string is forGeeks.
  • In the second <p> we are extracting a substring from the index 0 to 5 (excluding index 5) of the main string, the result printed is Geeks.
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