Java Examples in a Nutshell, 3rd Edition

Hello JSP2

The JSP 2.0 specification is a major step forward from the 1.x series. It includes support for a simple Java-like expression language (known as “EL”), which replaces awkward <%=...%> tags, and supports the Java Standard Tag Libraries (JSTL), which obviate the need for most <%...%> scriptlets. Example 20-5 is a version of Example 20-4, rewritten using these features. Note that <c:choose> and <c:when> tags serve as an if/else statement and replace the awkwardly intermingled HTML tags and Java scriptlets of Example 20-4. Also, notice that EL expressions are enclosed in ${...}, which is quite a bit friendlier than <%...%>. In this example, the @page directive is joined by an @taglib directive specifying that the page uses the standard “core” tag library and declares its XML namespace to be “c”.

Example 20-5. hello2.jsp

<%@page contentType='text/html'%>
<%-- The taglib directive specifies that we're using the JSTL 1.1 core taglib.
  -- If you're using 1.0, change to "http://java.sun.com/jstl/core_rt" --%>
<%@taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<c:choose>
  <c:when test='${param.name == null}'>
    <form>
    <i>Please enter your name: </i>
    <input name="name"/>
    <input type="Submit"/>
    </form>
  </c:when>
  <c:otherwise>
    Hello ${param.name}!
  </c:otherwise>
</c:choose>

Expression Language Syntax

A full tutorial on the Expression Language used in JSP 2 pages is beyond the scope of this chapter; you can find complete details in the JSP 2.0 specification. For now, however, ...