JSTL Custom Function : In this article I am going to teach you how to create custom JSTL
function. We had used many JSTL functions which are already in the lib.But if you want to
create a custom function for JSTL you need to follow some easy steps.
Step 1: Create tag library descriptor file which defines the configuration of custom function,
like it's class and the function which is open to use. Create the .tld file inside the 'WEB-
INF/tld/ ' directory .
/WEB-INF/tld/customTagLibrary.tld
<?xml version="1.0" encoding="UTF-8" ?>
<taglib version="2.0" xmlns="http://java.sun.com/xml/ns/j2ee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee web-jsptaglibrary_2_0.xsd">
<display-name>Custom EL Functions</display-name>
<tlib-version>1.0</tlib-version>
<short-name>cg</short-name>
<uri>/WEB-INF/tld/customTagLibrary</uri>
<function>
<name>getSum</name>
<function-class>com.evon.example.CustomELFunction</function-class>
<function-signature>
String getSum(int, int)
</function-signature>
</function>
</taglib>
Step 2 : Create an entry in web.xml for this tld file information:
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-
app_2_5.xsd" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" id="WebApp_ID" version="3.0">
<jsp-config>
<taglib>
<taglib-uri>/WEB-INF/tld/customTagLibrary</taglib-uri>
<taglib-location>/WEB-INF/tld/customTagLibrary.tld</taglib-location>
</taglib>
</jsp-config>
</web-app>
Step 3 : Create a class file which should match as described in function-class tag in tld
file. Note: Method signature must include static identifier.
CustomELFunction.java
package com.evon.example;
public class CustomELFunction {
public static String getSum(int x, int y){
int sum = x+y;
return sum;
}
}
Step 4 : Finally we need to create a jsp file, where we’re going to call custom function using
jstl. First we need to define the object of that taglib using jsp directives <%@ taglib %>.
Following the jsp which calling a custom JSTL method using Expression Language.
copytext
<%@ page language="java" contentType="text/html; charset=ISO-8859-1" pageEncoding="ISO-
8859-1"%>
<%@ taglib uri="/WEB-INF/tld/customTagLibrary" prefix="cg" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>Custom Function </title>
</head>
<body>
${cg:getSum(25+30) }
</body>
</html>
For such more Blogs kindly visit to http://findnerd.com/NerdDigest
function. We had used many JSTL functions which are already in the lib.But if you want to
create a custom function for JSTL you need to follow some easy steps.
Step 1: Create tag library descriptor file which defines the configuration of custom function,
like it's class and the function which is open to use. Create the .tld file inside the 'WEB-
INF/tld/ ' directory .
/WEB-INF/tld/customTagLibrary.tld
<?xml version="1.0" encoding="UTF-8" ?>
<taglib version="2.0" xmlns="http://java.sun.com/xml/ns/j2ee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee web-jsptaglibrary_2_0.xsd">
<display-name>Custom EL Functions</display-name>
<tlib-version>1.0</tlib-version>
<short-name>cg</short-name>
<uri>/WEB-INF/tld/customTagLibrary</uri>
<function>
<name>getSum</name>
<function-class>com.evon.example.CustomELFunction</function-class>
<function-signature>
String getSum(int, int)
</function-signature>
</function>
</taglib>
Step 2 : Create an entry in web.xml for this tld file information:
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-
app_2_5.xsd" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" id="WebApp_ID" version="3.0">
<jsp-config>
<taglib>
<taglib-uri>/WEB-INF/tld/customTagLibrary</taglib-uri>
<taglib-location>/WEB-INF/tld/customTagLibrary.tld</taglib-location>
</taglib>
</jsp-config>
</web-app>
Step 3 : Create a class file which should match as described in function-class tag in tld
file. Note: Method signature must include static identifier.
CustomELFunction.java
package com.evon.example;
public class CustomELFunction {
public static String getSum(int x, int y){
int sum = x+y;
return sum;
}
}
Step 4 : Finally we need to create a jsp file, where we’re going to call custom function using
jstl. First we need to define the object of that taglib using jsp directives <%@ taglib %>.
Following the jsp which calling a custom JSTL method using Expression Language.
copytext
<%@ page language="java" contentType="text/html; charset=ISO-8859-1" pageEncoding="ISO-
8859-1"%>
<%@ taglib uri="/WEB-INF/tld/customTagLibrary" prefix="cg" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>Custom Function </title>
</head>
<body>
${cg:getSum(25+30) }
</body>
</html>
For such more Blogs kindly visit to http://findnerd.com/NerdDigest
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