Functions

Table 6-8 lists the JSTL functions

Table 6-8 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

.

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 2 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: