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» XML support
<a
target="_blank"
href="https://github.com/pmd/pmd/blob/main/docs/pages/pmd/languages/xml.md"
class="float-right"
role="button"
><i class="fab fa-github fa-lg"></i> Edit on GitHub</a
>
</div>
</div>
<hr />
</header>
<div class="post-header">
<h1 class="post-title-main">XML support</h1>
</div>
<div class="post-content" data-github-edit-url="https://github.com/pmd/pmd/blob/main/docs/pages/pmd/languages/xml.md">
<div class="summary">XML-specific features and guidance</div>
<details id="inline-toc-details">
<summary>Table of Contents</summary>
<div id="inline-toc"><!-- empty, move TOC here when screen size too small --></div>
</details>
<details class="language-info">
<summary>Language Info for Maven POM
</summary>
<div class="card">
<ul class="list-group list-group-flush">
<li class="list-group-item">Since PMD 5.4.0</li>
<li class="list-group-item">Implementation: <a href="https://docs.pmd-code.org/apidocs/pmd-xml/7.8.0-SNAPSHOT/net/sourceforge/pmd/lang/xml/pom/PomLanguageModule.html#"><code>PomLanguageModule</code></a></li>
<li class="list-group-item">Id: pom</li>
<li class="list-group-item">PMD: ✔️</li>
<li class="list-group-item">CPD: ✔️</li>
</ul>
</div>
</details>
<details class="language-info">
<summary>Language Info for WSDL
</summary>
<div class="card">
<ul class="list-group list-group-flush">
<li class="list-group-item">Since PMD 5.4.0</li>
<li class="list-group-item">Implementation: <a href="https://docs.pmd-code.org/apidocs/pmd-xml/7.8.0-SNAPSHOT/net/sourceforge/pmd/lang/xml/wsdl/WsdlLanguageModule.html#"><code>WsdlLanguageModule</code></a></li>
<li class="list-group-item">Id: wsdl</li>
<li class="list-group-item">PMD: ✔️</li>
<li class="list-group-item">CPD: ✔️</li>
</ul>
</div>
</details>
<details class="language-info">
<summary>Language Info for XML
</summary>
<div class="card">
<ul class="list-group list-group-flush">
<li class="list-group-item">Since PMD 5.0.0</li>
<li class="list-group-item">Implementation: <a href="https://docs.pmd-code.org/apidocs/pmd-xml/7.8.0-SNAPSHOT/net/sourceforge/pmd/lang/xml/XmlLanguageModule.html#"><code>XmlLanguageModule</code></a></li>
<li class="list-group-item">Id: xml</li>
<li class="list-group-item">PMD: ✔️</li>
<li class="list-group-item">CPD: ✔️</li>
</ul>
</div>
</details>
<details class="language-info">
<summary>Language Info for XSL
</summary>
<div class="card">
<ul class="list-group list-group-flush">
<li class="list-group-item">Since PMD 5.0.0</li>
<li class="list-group-item">Implementation: <a href="https://docs.pmd-code.org/apidocs/pmd-xml/7.8.0-SNAPSHOT/net/sourceforge/pmd/lang/xml/xsl/XslLanguageModule.html#"><code>XslLanguageModule</code></a></li>
<li class="list-group-item">Id: xsl</li>
<li class="list-group-item">PMD: ✔️</li>
<li class="list-group-item">CPD: ✔️</li>
</ul>
</div>
</details>
<h2 id="the-xml-language-module">The XML language module</h2>
<p>PMD has an XML language module which exposes the <a href="https://de.wikipedia.org/wiki/Document_Object_Model">DOM</a>
of an XML document as an AST. Different flavours of XML are represented by separate
language instances, which all use the same parser under the hood. The following
table lists the languages currently provided by the <code class="language-plaintext highlighter-rouge">pmd-xml</code> maven module.</p>
<table>
<thead>
<tr>
<th>Language ID</th>
<th>Description</th>
</tr>
</thead>
<tbody>
<tr>
<td>xml</td>
<td>Generic XML language</td>
</tr>
<tr>
<td>pom</td>
<td>Maven Project Object Model (POM)</td>
</tr>
<tr>
<td>wsdl</td>
<td>Web Services Description Language</td>
</tr>
<tr>
<td>xsl</td>
<td>Extensible Stylesheet Language</td>
</tr>
</tbody>
</table>
<p>Each of those languages has a separate rule index, and may provide domain-specific
<a href="pmd_userdocs_extending_writing_xpath_rules.html#pmd-extension-functions">XPath functions</a>.
At their core they use the same parsing facilities though.</p>
<h3 id="file-attribution">File attribution</h3>
<p>Any file ending with <code class="language-plaintext highlighter-rouge">.xml</code> is associated with the <code class="language-plaintext highlighter-rouge">xml</code> language. Other XML flavours
use more specific extensions, like <code class="language-plaintext highlighter-rouge">.xsl</code>.</p>
<p>Some XML-based file formats do not conventionally use a <code class="language-plaintext highlighter-rouge">.xml</code> extension. To associate
these files with the XML language, you need to use the <code class="language-plaintext highlighter-rouge">--force-language xml</code> command-line
arguments, for instance:</p>
<div class="language-plaintext highlighter-rouge"><div class="highlight"><pre class="highlight"><code>$ pmd check -d /home/me/src/xml-file.ext -f text -R ruleset.xml --force-language xml
</code></pre></div></div>
<p>Please refer to <a href="pmd_userdocs_cli_reference.html#analyze-other-xml-formats">PMD CLI reference</a>
for more examples.</p>
<h3 id="xpath-rules-in-xml">XPath rules in XML</h3>
<p>While other languages use <a href="https://docs.pmd-code.org/apidocs/pmd-core/7.8.0-SNAPSHOT/net/sourceforge/pmd/lang/rule/xpath/XPathRule.html#"><code>XPathRule</code></a> to create XPath rules,
the use of this class is not recommended for XML languages. Instead, since 6.44.0, you
are advised to use <a href="https://docs.pmd-code.org/apidocs/pmd-xml/7.8.0-SNAPSHOT/net/sourceforge/pmd/lang/xml/rule/DomXPathRule.html#"><code>DomXPathRule</code></a>. This rule class interprets
XPath queries exactly as regular XPath, while <code class="language-plaintext highlighter-rouge">XPathRule</code> works on a wrapper for the
DOM which is inconsistent with the XPath spec. Since <code class="language-plaintext highlighter-rouge">DomXPathRule</code> conforms to the
XPath spec, you can</p>
<ul>
<li>test XML queries in any stock XPath testing tool, or use resources like StackOverflow
to help you write XPath queries.</li>
<li>match XML comments and processing instructions</li>
<li>use standard XPath functions like <code class="language-plaintext highlighter-rouge">text()</code> or <code class="language-plaintext highlighter-rouge">fn:string</code></li>
</ul>
<div class="alert alert-info" role="alert"><i class="fas fa-info-circle"></i> <b>Note:</b> The Rule Designer only works with <code class="language-plaintext highlighter-rouge">XPathRule</code>, and the tree it prints is inconsistent with the DOM representation used by <code class="language-plaintext highlighter-rouge">DomXPathRule</code>. You can use an online free XPath testing tool to test your query instead.</div>
<p>Heres an example declaration of a <code class="language-plaintext highlighter-rouge">DomXPathRule</code>:</p>
<div class="language-xml highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="nt">&lt;rule</span> <span class="na">name=</span><span class="s">"MyXPathRule"</span>
<span class="na">language=</span><span class="s">"xml"</span>
<span class="na">message=</span><span class="s">"A message"</span>
<span class="na">class=</span><span class="s">"net.sourceforge.pmd.lang.xml.rule.DomXPathRule"</span><span class="nt">&gt;</span>
<span class="nt">&lt;properties&gt;</span>
<span class="nt">&lt;property</span> <span class="na">name=</span><span class="s">"xpath"</span><span class="nt">&gt;</span>
<span class="nt">&lt;value&gt;</span><span class="cp">&lt;![CDATA[
/a/b/c[@attr = "5"]
]]&gt;</span><span class="nt">&lt;/value&gt;</span>
<span class="nt">&lt;/property&gt;</span>
<span class="c">&lt;!-- Note: the property "version" is unsupported. --&gt;</span>
<span class="nt">&lt;/properties&gt;</span>
<span class="nt">&lt;/rule&gt;</span>
</code></pre></div></div>
<p>The most important change is the <code class="language-plaintext highlighter-rouge">class</code> attribute, which doesnt point to <code class="language-plaintext highlighter-rouge">XPathRule</code>
but to <code class="language-plaintext highlighter-rouge">DomXPathRule</code>. Please see the Javadoc for <a href="https://docs.pmd-code.org/apidocs/pmd-xml/7.8.0-SNAPSHOT/net/sourceforge/pmd/lang/xml/rule/DomXPathRule.html#"><code>DomXPathRule</code></a>
for more info about the differences with <code class="language-plaintext highlighter-rouge">XPathRule</code>.</p>
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