Functions

Functions

Table 17-8 lists the JSTL functions

Table 17-8 Functions

Area

Function

Tags

Prefix

Functions

Collection length

length

fn

String
manipulation

toUpperCase, toLowerCase

substring, substringAfter, substringBefore

trim

replace

indexOf, startsWith, endsWith, contains, containsIgnoreCase

split, join

escapeXml

While the java.util.Collection interface defines a size method, it does not conform to the JavaBeans design pattern for properties and cannot be accessed via the JSP expression language. The length function can be applied to any collection supported by the c:forEach and returns the length of the collection. When applied to a String, it returns the number of characters in the string.

For example, the greeting.jsp page of the hello2 application introduced in Updating Web Applications uses the fn:length function and c:if tag to determine whether to include a response page:
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" 
  prefix="c" %>
<%@ taglib uri="http://java.sun.com/jsp/jstl/functions"
  prefix="fn" %>
<html>
<head><title>Hello</title></head>
...
<input type="text" name="username" size="25">
<p></p>
<input type="submit" value="Submit">
<input type="reset" value="Reset">
</form>

<c:if test="${fn:length(param.username) > 0}" >
  <%@include file="response.jsp" %>
</c:if>
</body>
</html> 
The rest of the JSTL functions are concerned with string manipulation:

toUpperCase, toLowerCase - Changes the capitalization of a string.

substring, substringBefore, substringAfter - Gets a subset of a string.

trim - Trims whitespace from a string.

replace - Replaces characters in a string.

indexOf, startsWith, endsWith, contains, containsIgnoreCase - Checks if a string contains another string.

split - Splits a string into an array.

join - Joins a collection into a string.

escapeXml - Escapes XML characters in a string.

Table 17-8 Functions
Area	Function	Tags	Prefix
Functions	Collection length	length	fn
String manipulation	`toUpperCase, toLowerCase` `substring, substringAfter, substringBefore` `trim` `replace` `indexOf, startsWith, endsWith, contains, containsIgnoreCase` `split, join` `escapeXml`

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