JSTL fn:indexOf() Function

Last Updated : 14 Dec, 2023

For JSTL-based applications, fn:indexOf() function is used to get the first occurrence index or the position of the substring in the main string. This function-

returns the position of the substring if it is found in the main string.
If it is not found, then it returns the -1 value and prints on the screen.

In this article, we will see the syntax of this function its parameters, and the example with the output and explanation.

Syntax of fn:indexOf() Function

${fn:indexOf(string, substring)}

where,

string: This is the input or specified sting in which we are searching for the substring.
substring: This is the string to be located within the input string. If it is found the index is been returned or else the -1 is been returned.

Example of JSTL fn:indexOf() Function

Below is the implementation of JSTL fn:indexOf() Function:

HTML

<%@ page contentType="text/html;charset=UTF-8" language="java" %> 
<%@ taglib uri="http://java.sun.com/jsp/jstl/functions" prefix="fn" %> 
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %> 
    
<html> 
  <head> 
      <title>JSTL fn:indexOf() Example</title> 
  </head> 
  <body> 
    <c:set var="inputString" value="Welcome to GeeksforGeeks"/> 
    <c:set var="substringToFind" value="Geeks"/> 
    <h3>Original String: ${inputString}</h3> 
    <h3>Substring to Find: ${substringToFind}</h3> 
      
        <c:set var="indexOfSubstring" value="${fn:indexOf(inputString, substringToFind)}"/> 
      
    <h3>Index of Substring: ${indexOfSubstring}</h3> 
  </body> 
</html> 

Output:

Original String: Welcome to GeeksforGeeks
Substring to Find: Geeks
Index of Substring: 11

Output Screen of JSTL fn:indexOf() Function:

Output Screen of JSTL fn:indexOf() Function

Explanation of the above Program:

we have stored the “Welcome to GeeksforGeeks” value in the inputString variable.
Then we are using the fn:indexOf() function to find the first occurrence of the given substring (Geeks) within the inputString.
We can see that the first occurent of Geeks substring is at position 11. So the function has returned this value and we printed that value using the HTML tag <p>.

Suggest improvement

JSTL fn:trim() Function

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