JavaServer Pages, Second Edition

Action Elements

Action elements use XML element syntax and represent components that are invoked when a client requests the JSP page. They may encapsulate functionality such as input validation using beans, database access, or passing control to another page. The JSP specification defines a few standard action elements, described in this section, and also includes a framework for developing custom action elements.

An action element consists of a start tag (optionally with attributes), a body, and an end tag. Other elements can be nested in the body. Here’s an example:

<jsp:forward page="nextPage.jsp">
  <jsp:param name="aParam" value="aValue" />
</jsp:forward>

If the action element doesn’t have a body, a shorthand notation can be used where the start tag ends with "/>" instead of ">“, as shown by the <jsp:param> param action in this example. The action element name and attribute names are case-sensitive.

Some standard action attributes accept a request-time attribute value (marked with “RT expression” in the “Dynamic value accepted” column in the Attributes table for each action that follows), using the JSP expression syntax:

<% String headerPage = currentTemplateDir + "/header.jsp"; %>
<jsp:include page="<%= headerPage %>" />

The attribute descriptions for each action in this section define whether a request-time attribute value is accepted or not.

JSTL actions, described in Appendix B, and custom actions may accept JSTL Expression Language (EL) expressions for dynamic values instead ...