Functions - The J2EE 1.4 Tutorial

Functions

Table 14-9 lists the JSTL functions

Table 14-9 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

.

Although the java.util.Collection interface defines a size method, it does not conform to the JavaBeans component design pattern for properties and so 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 index.jsp page of the hello1 application introduced in Chapter 3 uses the fn:length function and the 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 whether 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

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