The fn:startsWith function is a JSTL function that checks whether a string starts with a specified prefix. The function takes two arguments: a string to check and a prefix to test against. It returns true if the string starts with the prefix and false otherwise.

The syntax of the fn:startsWith function is as follows:

${fn:startsWith(string, prefix)}

where string is the string to check and prefix is the prefix to test against.

For example, the following expression checks whether the string "hello, world" starts with the prefix "hello":

${fn:startsWith("hello, world", "hello")}

This expression returns true.

You can also use variables instead of literals for the arguments. For example, if you have a variable text containing a string and a variable prefix containing a prefix, you can check whether the string starts with the prefix using the following expression:

${fn:startsWith(text, prefix)}

This expression returns true if the string stored in the text variable starts with the prefix stored in the prefix variable, and false otherwise.

Note that the fn tag library must be imported at the beginning of the JSP page using the following tag:

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