JavaServer Pages, 3rd Edition

Accessing Attribute Values

The tag file in Example 11-1 is too simple to illustrate all that you can do with tag files. For instance, most real-world tag files are controlled through attribute values set by the page author. You may recall from Chapter 7 that the <ora:motd> custom action has a category attribute for selecting the message category that messages should be picked from. Example 11-2 shows how a tag file implementation of the <ora:motd> action declares, accesses, and uses this attribute value.

Example 11-2. Using attributes in a tag file (motd.tag)

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

<jsp:useBean id="mmb" class="com.ora.jsp.beans.motd.MixedMessageBean" />
<c:set target="${mmb}" property="category" value="${category}" />
${mmb.message}

Each attribute must be declared with an attribute directive in a tag file. In Example 11-2, the category attribute is declared using an attribute directive with the name attribute set to category. The required attribute is set to true, meaning that the page author must specify a value for the category attribute; the container complains if the attribute is missing. The default value for required is false, so you can leave it out for attributes that are optional.

Another attribute of the attribute directive, not used in Example 11-2, is rtexprvalue . A value of true means that the author can specify the value either as a static string ...