xalan-j/xsltc/xsl_if_design.html (183 lines of code) (raw):
<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html>
<head>
<title>ASF: <xsl:if></title>
<meta http-equiv="content-type" content="text/html; charset=UTF-8" />
<meta http-equiv="Content-Style-Type" content="text/css" />
<link rel="stylesheet" type="text/css" href="resources/apache-xalan.css" />
</head>
<!--
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
-->
<body>
<div id="title">
<table class="HdrTitle">
<tbody>
<tr>
<th rowspan="2">
<a href="../index.html">
<img alt="Trademark Logo" src="resources/XalanJ-Logo-tm.png" width="190" height="90" />
</a>
</th>
<th text-align="center" width="75%">
<a href="index.html">XSLTC Design</a>
</th>
</tr>
<tr>
<td valign="middle"><xsl:if></td>
</tr>
</tbody>
</table>
<table class="HdrButtons" align="center" border="1">
<tbody>
<tr>
<td>
<a href="http://www.apache.org">Apache Foundation</a>
</td>
<td>
<a href="http://xalan.apache.org">Xalan Project</a>
</td>
<td>
<a href="http://xerces.apache.org">Xerces Project</a>
</td>
<td>
<a href="http://www.w3.org/TR">Web Consortium</a>
</td>
<td>
<a href="http://www.oasis-open.org/standards">Oasis Open</a>
</td>
</tr>
</tbody>
</table>
</div>
<div id="navLeft">
<ul>
<li>
<a href="index.html">Overview</a>
</li></ul><hr /><ul>
<li>
<a href="xsltc_compiler.html">Compiler design</a>
</li></ul><hr /><ul>
<li>
<a href="xsl_whitespace_design.html">Whitespace</a>
</li>
<li>
<a href="xsl_sort_design.html">xsl:sort</a>
</li>
<li>
<a href="xsl_key_design.html">Keys</a>
</li>
<li>
<a href="xsl_comment_design.html">Comment design</a>
</li></ul><hr /><ul>
<li>
<a href="xsl_lang_design.html">lang()</a>
</li>
<li>
<a href="xsl_unparsed_design.html">Unparsed entities</a>
</li></ul><hr /><ul>
<li>If design<br />
</li>
<li>
<a href="xsl_choose_design.html">Choose|When|Otherwise design</a>
</li>
<li>
<a href="xsl_include_design.html">Include|Import design</a>
</li>
<li>
<a href="xsl_variable_design.html">Variable|Param design</a>
</li></ul><hr /><ul>
<li>
<a href="xsltc_runtime.html">Runtime</a>
</li></ul><hr /><ul>
<li>
<a href="xsltc_dom.html">Internal DOM</a>
</li>
<li>
<a href="xsltc_namespace.html">Namespaces</a>
</li></ul><hr /><ul>
<li>
<a href="xsltc_trax.html">Translet & TrAX</a>
</li>
<li>
<a href="xsltc_predicates.html">XPath Predicates</a>
</li>
<li>
<a href="xsltc_iterators.html">Xsltc Iterators</a>
</li>
<li>
<a href="xsltc_native_api.html">Xsltc Native API</a>
</li>
<li>
<a href="xsltc_trax_api.html">Xsltc TrAX API</a>
</li>
<li>
<a href="xsltc_performance.html">Performance Hints</a>
</li>
</ul>
</div>
<div id="content">
<h2><xsl:if></h2>
<p align="right" size="2">
<a href="#content">(top)</a>
</p>
<h3>Contents</h3>
<ul>
<li>
<a href="#functionality">Functionality</a>
</li>
<li>
<a href="#implementation">Implementation</a>
</li>
</ul>
<a name="functionality"></a>
<p align="right" size="2">
<a href="#content">(top)</a>
</p>
<h3>Functionality</h3>
<p>This element is cruical to XSL processing, but still very simple both in
its use and implementation. The element is used like this:</p>
<blockquote class="source">
<pre>
<xsl:if test="contains($the-world,'Elvis')">
<xsl:message>Elvis is still alive!</xsl:message>
</xsl:if></pre>
</blockquote>
<p>The element's contents will only be executed if the test succeeds. There
is no <code><xsl:else></code> element. One has to use either several
<code><xsl:if></code>-elements or use a choose-element.</p>
<a name="implementation"></a>
<p align="right" size="2">
<a href="#content">(top)</a>
</p>
<h3>Implementation</h3>
<p>The basic implementation is very simple:</p>
<ul>
<li>execute the expression from the 'test'-attribute</li>
<li>evaluate the resulting boolean value</li>
<li>ignore the element contents if the value is 'false'</li>
<li>otherwise execute the element contents</li>
</ul>
<p>There is onle type of function call that makes this a bit more complicated.
The <code>function-available()</code> and <code>element-available()</code>
function calls can be used to test for extension elements and functions. A
very common use for these is to encapsulate all references to extension
elements inside an <code><xsl:if></code> element and test for the
existance of this element before attempting to use it. XSLTC has to support
this. Otherwise we may risk either outputting erronuous error or warning
messages about acessing non-existing elements, or even worse, compiling in
calls to non-existing methods in the translet, causing the JVM's verifier to
prevent the translet from being loaded.</p>
<p>The <code>function-available()</code> and <code>element-available()</code>
functions have been updated to perform an evaluation at compile-time, so that
the <code>If</code> class can know wether to compile in calls to extensions or
not. This is possible because both functions take only literal expressions as
parameters. See the <code>getResult()</code> methods of the
<code>FunctionAvailableCall</code> and <code>ElementAvailableCall</code>
classes for details.</p>
<p align="right" size="2">
<a href="#content">(top)</a>
</p>
</div>
<div id="footer">Copyright © 1999-2014 The Apache Software Foundation<br />Apache, Xalan, and the Feather logo are trademarks of The Apache Software Foundation<div class="small">Web Page created on - Thu 2014-05-15</div>
</div>
</body>
</html>