JavaServer Pages, 3rd Edition

Creating and Using a Tag File

A tag file is a text file that contains JSP elements implementing the functionality of a custom action. You must use a .tag ^[1] filename extension to identify this type of file to the web container. All JSP elements that you can use in a JSP file can also be used in a tag file, with exception to the page directive (a tag file is not a page). There are also a few JSP directives that are only allowed in a tag file, as you will see shortly. Apart from that, creating a tag file is no different than creating a JSP page. Once created and installed, a tag file is used the same as the custom actions implemented in Java that you’ve seen in previous chapters.

Example 11-1 shows a very simple tag file.

Example 11-1. Simple tag file (copyright.tag)

                  <%@ tag body-content="empty" %>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>

<jsp:useBean id="now" scope="application" class="java.util.Date" />
Copyright &copy; ${now.year + 1900} My Company

This tag file inserts a copyright statement with the current year in the calling page. The first line is a tag directive. You may use attributes of this directive to specify a description, icon, or an example that a page-authoring tool can show the designer. Other attributes let you specify whether EL expressions should be processed, as well as various information related to scripting code, i.e., the same type of information as you specify with the page directive in JSP pages. All of these attributes are described ...