JavaServer Pages, 3rd Edition

Exposing Data to the Calling Page Through Variables

Attributes provide input to a custom action, but sometimes you also need to give the page that contains the custom action access to data produced by the custom action. For instance, the <my:forEvenAndOdd> action is not all that useful unless the page can access the current iteration value in the fragments for even and odd rows. To handle this requirement, data can be passed from a custom action to the caller by exposing it through declared variables.

Example 11-6 shows a version of the tag file from Example 11-5 that’s been extended to expose the current iteration value as a variable named current. All differences between the examples are highlighted.

Example 11-6. Exporting data through variables (forEvenAndOdd2.tag)

<%@ tag body-content="empty" %>
<%@ attribute name="items" rtexprvalue="true" required="true" %>
<%@ attribute name="even" fragment="true" required="true" %>
<%@ attribute name="odd" fragment="true" required="true" %>
<%@ variable name-given="current" variable-class="java.lang.Object"
  scope="NESTED" %>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>

<c:forEach items="${items}" varStatus="status" var="current">
  <c:choose>
    <c:when test="${status.count % 2 == 0}">
      <jsp:invoke fragment="even" />
    </c:when>
    <c:otherwise>
      <jsp:invoke fragment="odd" />
    </c:otherwise>
  </c:choose>
</c:forEach>

The variable directive declares the variable. The name-given attribute specifies its name and the variable-class attribute ...