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<?xml version="1.0" encoding="UTF-8"?>
<document xmlns="http://maven.apache.org/XDOC/2.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/XDOC/2.0 http://maven.apache.org/xsd/xdoc-2.0.xsd">
<head>
<title>Writing Filters</title>
<script type="text/javascript" src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.3/jquery.min.js"/>
<script type="text/javascript" src="js/anchors.js"/>
<script type="text/javascript" src="js/google-analytics.js"/>
<link rel="icon" href="images/favicon.png" type="image/x-icon" />
<link rel="shortcut icon" href="images/favicon.ico" type="image/ico" />
</head>
<body>
<section name="Content">
<macro name="toc">
<param name="fromDepth" value="1"/>
<param name="toDepth" value="1"/>
</macro>
</section>
<section name="Overview">
<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>
<img src="images/Filter.gif" alt="Filter UML diagram" />
</section>
<section name="Writing Filters">
<p>
The <code>Filter</code> that we demonstrate here rejects
audit events for files whose name matches a <a
href="property_types.html#regexp">regular expression</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>
<source>
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);
}
}
</source>
</section>
<section name="Declare check's external resource locations">
<p>
See <a href="writingchecks.html#Declare_checks_external_resource_locations">Declare check's external resource locations</a>.
</p>
</section>
<section name="Using Filters">
<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>
<source>
<module name="com.mycompany.filters.FilesFilter">
<property name="files" value="Generated"/>
</module>
</source>
</section>
<section name="Huh? I can't figure it out!">
<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 name="Contributing">
<p>
We need <em>your</em> 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>
</body>
</document>
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