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writingfilters.html
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writingfilters.html
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<!DOCTYPE html>
<!--
| Generated by Apache Maven Doxia Site Renderer 1.11.1 from src/xdocs/writingfilters.xml at 2024-04-28
| Rendered using Apache Maven Default Skin
-->
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
<head>
<meta charset="UTF-8" />
<meta name="viewport" content="width=device-width, initial-scale=1.0" />
<meta name="generator" content="Apache Maven Doxia Site Renderer 1.11.1" />
<title>checkstyle – Writing Filters</title>
<link rel="stylesheet" href="./css/maven-base.css" />
<link rel="stylesheet" href="./css/maven-theme.css" />
<link rel="stylesheet" href="./css/site.css" />
<link rel="stylesheet" href="./css/print.css" media="print" />
<script type="text/javascript" src="./js/checkstyle.js"></script>
<script type="text/javascript"
src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.3/jquery.min.js"></script>
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</head>
<body class="composite">
<div id="banner">
<a href="./" id="bannerLeft" title="Checkstyle"><img src="images/header-checkstyle-logo.png" alt="Checkstyle"/></a><a href="./" id="bannerRight" title="Checkstyle"><img src="images/header-right-ruller.png" alt="Checkstyle"/></a> <div class="clear">
<hr/>
</div>
</div>
<div id="breadcrumbs">
<div class="xright"><a href="" title="toTop">toTop</a> | <span id="publishDate">Last Published: 2024-04-28</span>
| <span id="projectVersion">Version: 10.16.0</span>
</div>
<div class="clear">
<hr/>
</div>
</div>
<div id="leftColumn">
<div id="navcolumn">
<h5>About</h5>
<ul>
<li class="none"><a href="index.html" title="Checkstyle">Checkstyle</a></li>
<li class="none"><a href="releasenotes.html" title="Release Notes">Release Notes</a></li>
<li class="none"><a href="consulting.html" title="Consulting">Consulting</a></li>
<li class="none"><a href="sponsoring.html" title="Sponsoring">Sponsoring</a></li>
</ul>
<h5>Documentation</h5>
<ul>
<li class="expanded"><a href="config.html" title="Configuration">Configuration</a>
<ul>
<li class="none"><a href="property_types.html" title="Property Types">Property Types</a></li>
<li class="none"><a href="config_system_properties.html" title="System Properties">System Properties</a></li>
</ul></li>
<li class="expanded"><a href="running.html" title="Running">Running</a>
<ul>
<li class="none"><a href="anttask.html" title="Ant Task">Ant Task</a></li>
<li class="none"><a href="cmdline.html" title="Command Line">Command Line</a></li>
</ul></li>
<li class="expanded"><a href="checks.html" title="Checks">Checks</a>
<ul>
<li class="collapsed"><a href="checks/annotation/index.html" title="Annotations">Annotations</a></li>
<li class="collapsed"><a href="checks/blocks/index.html" title="Block Checks">Block Checks</a></li>
<li class="collapsed"><a href="checks/design/index.html" title="Class Design">Class Design</a></li>
<li class="collapsed"><a href="checks/coding/index.html" title="Coding">Coding</a></li>
<li class="collapsed"><a href="checks/header/index.html" title="Headers">Headers</a></li>
<li class="collapsed"><a href="checks/imports/index.html" title="Imports">Imports</a></li>
<li class="collapsed"><a href="checks/javadoc/index.html" title="Javadoc Comments">Javadoc Comments</a></li>
<li class="collapsed"><a href="checks/metrics/index.html" title="Metrics">Metrics</a></li>
<li class="collapsed"><a href="checks/misc/index.html" title="Miscellaneous">Miscellaneous</a></li>
<li class="collapsed"><a href="checks/modifier/index.html" title="Modifiers">Modifiers</a></li>
<li class="collapsed"><a href="checks/naming/index.html" title="Naming Conventions">Naming Conventions</a></li>
<li class="collapsed"><a href="checks/regexp/index.html" title="Regexp">Regexp</a></li>
<li class="collapsed"><a href="checks/sizes/index.html" title="Size Violations">Size Violations</a></li>
<li class="collapsed"><a href="checks/whitespace/index.html" title="Whitespace">Whitespace</a></li>
</ul></li>
<li class="collapsed"><a href="filters/index.html" title="Filters">Filters</a></li>
<li class="collapsed"><a href="filefilters/index.html" title="File Filters">File Filters</a></li>
<li class="expanded"><a href="style_configs.html" title="Style Configurations">Style Configurations</a>
<ul>
<li class="none"><a href="google_style.html" title="Google's Style">Google's Style</a></li>
<li class="none"><a href="sun_style.html" title="Sun's Style">Sun's Style</a></li>
</ul></li>
</ul>
<h5>Developers</h5>
<ul>
<li class="expanded"><a href="extending.html" title="Extending Checkstyle">Extending Checkstyle</a>
<ul>
<li class="none"><a href="writingchecks.html" title="Writing Checks">Writing Checks</a></li>
<li class="none"><a href="writingjavadocchecks.html" title="Writing Javadoc Checks">Writing Javadoc Checks</a></li>
<li class="none"><strong>Writing Filters</strong></li>
<li class="none"><a href="writingfilefilters.html" title="Writing File Filters">Writing File Filters</a></li>
<li class="none"><a href="writinglisteners.html" title="Writing Listeners">Writing Listeners</a></li>
</ul></li>
<li class="none"><a href="contributing.html" title="Contributing">Contributing</a></li>
<li class="expanded"><a href="beginning_development.html" title="Beginning Development">Beginning Development</a>
<ul>
<li class="none"><a href="eclipse.html" title="Eclipse IDE">Eclipse IDE</a></li>
<li class="none"><a href="netbeans.html" title="NetBeans IDE">NetBeans IDE</a></li>
<li class="none"><a href="idea.html" title="IntelliJ IDE">IntelliJ IDE</a></li>
</ul></li>
<li class="none"><a href="apidocs/index.html" title="Javadoc">Javadoc</a></li>
</ul>
<h5>Project Documentation</h5>
<ul>
<li class="collapsed"><a href="project-info.html" title="Project Information">Project Information</a></li>
<li class="collapsed"><a href="project-reports.html" title="Project Reports">Project Reports</a></li>
</ul>
<a href="https://github.com/checkstyle/checkstyle" title="GitHub" class="poweredBy">
<img class="poweredBy" alt="GitHub" src="images/github_logo_social_coding_outlined.png" />
</a>
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<img class="poweredBy" alt="JProfiler" src="https://www.ej-technologies.com/images/product_banners/jprofiler_medium.png" />
</a>
</div>
</div>
<div id="bodyColumn">
<div id="contentBox">
<section>
<h2><a name="Content"></a>Content</h2>
<ul>
<li><a href="#Content">Content</a></li>
<li><a href="#Overview">Overview</a></li>
<li><a href="#Writing_Filters">Writing Filters</a></li>
<li><a href="#Declare_check.27s_external_resource_locations">Declare check's external resource locations</a></li>
<li><a href="#Using_Filters">Using Filters</a></li>
<li><a href="#Huh.3F_I_can.27t_figure_it_out.21">Huh? I can't figure it out!</a></li>
<li><a href="#Contributing">Contributing</a></li></ul>
</section>
<section>
<h2><a name="Overview"></a>Overview</h2>
<p>
A <code>Checker</code> has a set of <code>Filter</code>s that decide which audit events
the <code>Checker</code> reports through its listeners. Interface <code>Filter</code>
and class <code>FilterSet</code> are intended to support general <code>AuditEvent</code>
filtering using a set of <code>Filter</code>s.
</p>
<p>
A <code>Filter</code> has <code>boolean</code> method <code>accept(AuditEvent)</code> that
returns <code>true</code> if the <code>Filter</code> accepts the <code>AuditEvent</code>
parameter and returns <code>false</code> if the <code>Filter</code> rejects it.
</p>
<p>
A <code>FilterSet</code> is a particular <code>Filter</code> that contains a set of
<code>Filter</code>s. A <code>FilterSet</code> accepts an <code>AuditEvent</code> if and
only if all <code>Filter</code>s in the set accept the <code>AuditEvent</code>.
</p>
<p>
Here is a UML diagram for interface <code>Filter</code>
and class <code>FilterSet</code>.
</p>
<div class="wrapper">
<img src="images/Filter.gif" alt="Filter UML diagram" />
</div>
</section>
<section>
<h2><a name="Writing_Filters"></a>Writing Filters</h2>
<p>
The <code>Filter</code> that we demonstrate here rejects
audit events for files whose name matches a <a href="property_types.html#Pattern">Pattern</a>. In order to
enable the specification of the file name pattern as a property in a
configuration file, the <code>Filter</code> is an <a href="apidocs/com/puppycrawl/tools/checkstyle/api/AutomaticBean.html">AutomaticBean</a>
with mutator method <code>setFiles(String)</code> that
receives the file name pattern. An <code>AutomaticBean</code> uses JavaBean
introspection to set JavaBean properties such as <code>files</code>.
</p>
<div class="source">
<pre>
package com.mycompany.filters;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
import java.util.regex.PatternSyntaxException;
import com.puppycrawl.tools.checkstyle.api.AuditEvent;
import com.puppycrawl.tools.checkstyle.api.AutomaticBean;
import com.puppycrawl.tools.checkstyle.api.Filter;
import com.puppycrawl.tools.checkstyle.api.Utils;
public class FilesFilter
extends AutomaticBean
implements Filter
{
private Pattern mFileRegexp;
public FilesFilter()
throws PatternSyntaxException
{
setFiles("^$");
}
public boolean accept(AuditEvent aEvent)
{
final String fileName = aEvent.getFileName();
return ((fileName == null) || !mFileRegexp.matcher(fileName).find());
}
public void setFiles(String aFilesPattern)
throws PatternSyntaxException
{
mFileRegexp = Utils.getPattern(aFilesPattern);
}
}
</pre></div>
</section>
<section>
<h2><a name="Declare_check.27s_external_resource_locations"></a>Declare check's external resource locations</h2>
<p>
See <a href="writingchecks.html#Declare_check.27s_external_resource_locations">
Declare check's external resource locations</a>.
</p>
</section>
<section>
<h2><a name="Using_Filters"></a>Using Filters</h2>
<p>
To incorporate a <code>Filter</code> in the filter set
for a <code>Checker</code>, include a module element for
the <code>Filter</code> in the <a href="config.html#Filters">configuration file</a>. For example, to
configure a <code>Checker</code> so that it uses custom
filter <code>FilesFilter</code> to prevent reporting of
audit events for files whose name contains "Generated",
include the following module in the configuration file:
</p>
<div class="source">
<pre>
<module name="com.mycompany.filters.FilesFilter">
<property name="files" value="Generated"/>
</module>
</pre></div>
</section>
<section>
<h2><a name="Huh.3F_I_can.27t_figure_it_out.21"></a>Huh? I can't figure it out!</h2>
<p>
That's probably our fault, and it means that we have to provide
better documentation. Please do not hesitate to ask questions on the
user mailing list, this will help us to improve this document. Please
ask your questions as precisely as possible. We will not be able to
answer questions like "I want to write a filter but I don't
know how, can you help me?". Tell us what you are trying to do
(the purpose of the filter), what you have understood so far, and what
exactly you are getting stuck on.
</p>
</section>
<section>
<h2><a name="Contributing"></a>Contributing</h2>
<p>
We need <i>your</i> help to keep improving Checkstyle. Whenever you
write a filter that you think is generally useful, please consider <a href="contributing.html">contributing</a> it to the Checkstyle
community and submit it for inclusion in the next release of
Checkstyle.
</p>
</section>
</div>
</div>
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