spring-security/etc/checkstyle/checkstyle.xml

<?xml version="1.0"?>
<!DOCTYPE module PUBLIC "-//Puppy Crawl//DTD Check Configuration 1.3//EN"
		"https://www.puppycrawl.com/dtds/configuration_1_3.dtd">
<module name="Checker">
	<!-- Suppressions -->
	<module name="SuppressionFilter">
		<property name="file" value="${configDir}/suppressions.xml"/>
	</module>
	
	<!-- Root Checks -->
	<module name="RegexpHeader">
		<property name="headerFile" value="${configDir}/header.txt"/>
		<property name="fileExtensions" value="java"/>
	</module>

	<!-- Root Checks -->
	<module name="TreeWalker">
		<!-- Regexp -->
		<module name="RegexpSinglelineJava">
			<property name="format" value="^\t* +\t*\S"/>
			<property name="message" value="Line has leading space characters; indentation should be performed with tabs only."/>
			<property name="ignoreComments" value="true"/>
		</module>
		<module name="RegexpSinglelineJava">
			<property name="maximum" value="0"/>
			<property name="format" value="org\.junit\.Assert\.assert"/>
			<property name="message" value="Please use AssertJ imports."/>
			<property name="ignoreComments" value="true"/>
		</module>
		<module name="Regexp">
			<property name="format" value="[ \t]+$"/>
			<property name="illegalPattern" value="true"/>
			<property name="message" value="Trailing whitespace"/>
		</module>
	</module>
</module>