Creating Custom JSP Tags

May

Creating Custom JSP Tags

Written by rsakowski Posted in: Java EE, JSP

Tag files contain JSP elements that define a custom action. A JSP tag file is similar to a normal JSP file with three exceptions:

The page directive is not allowed in a tag file.
There are certain JSP directives that are only allowed in a tag file.
The file name extension for a tag file is “.tag”.

Everything else is the same as creating a JSP page.

Using custom JSP tag files provide a number of benefits:

Promotes reusability
Enhances loose coupling
Creates single point of maintenance
Allows a clear division of labor between technical and esthetic skill sets

The following is a JSP page that uses a custom tag. For all intents and purposes, it eliminates coding from the page with the exceptions of the directives and the me prefix on the sayHello element.

<%@ page language="java" pageEncoding="ISO-8859-1"%>
<%@ taglib prefix="me" tagdir="/WEB-INF/tags" %>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
	<head>
		<title>Hello with Custom Tag</title>
	</head>
	<body>
		<me:sayHello firstName="Roger" lastName="Sakowski"/>
	</body>
</html>

When this page is viewed in a browser, it will provide the following display:
Hello with Custom JSP tag

Here is the custom tag (sayHello.tag) used in the JSP example page above:

<%@ tag body-content="empty" %>
<%@ attribute name="firstName" required="true" rtexprvalue="true" %>
<%@ attribute name="lastName" required="true" rtexprvalue="true" %>
<jsp:useBean id="bean" class="com.webucator.beans.YourName" />
<jsp:setProperty name="bean" property="firstName" value="#{firstName}" />
<jsp:setProperty name="bean" property="lastName" value="#{lastName}" />
<jsp:getProperty name="bean" property="greeting" />

Note the directives. They declare the required attributes firstName and lastName. These attributes were used in expressions to set the values on a JavaBean. Here is the JavaBean (YourName.java) used by this tag:

package com.webucator.beans;
public class YourName {
	private String firstName;
	private String lastName;
	public YourName() {}
	public String getGreeting() {
		return "<h1>Hello, " + firstName + " " + lastName + "!</h1>";
	}
	public void setFirstName(String firstName) {
		this.firstName = firstName;
	}
	public void setLastName(String lastName) {
		this.lastName = lastName;
	}
}

This brings me back to the benefits or custom JSP tags that I listed at the beginning of this article:

Promotes reusability: The tag can be used in any number of JSP pages that need it.
Enhances loose coupling: The JSP page is completely decoupled from the underlining code.
Creates single point of maintenance: Changes made to the tag will also change the JSP documents that use it.
Allows a clear division of labor between technical and aesthetic skill sets: It frees page designers to deal with design while freeing programmers to focus on programming.

In short, it is a win/win proposition for web application development in general.

In my upcoming articles I will cover Java frameworks in general and explore the most popular.

Custom tags are covered in our Introduction to JSP, Advanced JSP, and Comprehensive JSP classes.

No TweetBacks yet. (Be the first to Tweet this post)