checkstyle.xml

<?xml version="1.0"?>
<!DOCTYPE module PUBLIC "-//Puppy Crawl//DTD Check Configuration 1.3//EN" "http://www.puppycrawl.com/dtds/configuration_1_3.dtd">
<module name="Checker">
	<!-- CREDIT TO THE FABRIC TEAM FOR THE BASE CHECKSTYLE XML FILE -->
	<property name="charset" value="UTF-8"/>
	<property name="fileExtensions" value="java"/>
	<property name="localeLanguage" value="en"/>
	<property name="localeCountry" value="US"/>
	<property name="tabWidth" value="4"/>

	<!-- disallow trailing whitespace -->
	<module name="RegexpSingleline">
		<property name="format" value="\s+$"/>
		<property name="message" value="trailing whitespace"/>
	</module>

	<!-- note: RegexpMultiline shows nicer messages than Regexp, but has to be outside TreeWalker -->
	<!-- disallow multiple consecutive blank lines -->
	<module name="RegexpMultiline">
		<property name="format" value="\n[\t ]*\r?\n[\t ]*\r?\n"/>
		<property name="message" value="adjacent blank lines"/>
	</module>

	<module name="TreeWalker">
        <!-- Allow "//CHECKSTYLE.OFF: <InspectionName>" and "//CHECKSTYLE.ON: <InspectionName>" pairs to toggle some inspections -->
        <module name="SuppressionCommentFilter">
            <property name="offCommentFormat" value="CHECKSTYLE.OFF\: ([\w\|]+)"/>
            <property name="onCommentFormat" value="CHECKSTYLE.ON\: ([\w\|]+)"/>
            <property name="checkFormat" value="$1"/>
        </module>

		<!-- Ensure all imports are ship shape -->
		<module name="IllegalImport"/>
		<module name="RedundantImport"/>
		<module name="UnusedImports"/>

		<module name="AnnotationLocation"/>
		<module name="MissingOverride"/>

        <module name="MatchXpath">
            <property name="query" value="//ANNOTATION/IDENT[@text='NotNull']"/>
            <message key="matchxpath.match" value="@NotNull annotation is not allowed"/>
        </module>
	</module>
</module>