extras/checkstyle.xml

<?xml version="1.0"?>
<!DOCTYPE module PUBLIC
          "-//Checkstyle//DTD Checkstyle Configuration 1.3//EN"
          "https://checkstyle.org/dtds/configuration_1_3.dtd">

<module name="Checker">
  <!--
      If you set the basedir property below, then all reported file
      names will be relative to the specified directory. See
      https://checkstyle.org/config.html#Checker

      <property name="basedir" value="${basedir}"/>
  -->

  <metadata name="org.checkstyle.principle" value="Practice What You Preach"/>
  <metadata name="org.checkstyle.principle.description"
            value="In our config we should use all Checks that Checkstyle has"/>

  <property name="cacheFile" value="${checkstyle.cache.file}"/>

  <property name="severity" value="error"/>

  <property name="fileExtensions" value="java, properties, xml, vm, g, g4, dtd"/>

  <!-- BeforeExecutionFileFilters is required for sources that are based on java9 -->
  <module name="BeforeExecutionExclusionFileFilter">
    <property name="fileNamePattern" value="module\-info\.java$" />
  </module>

  <!-- Filters -->
  <module name="SeverityMatchFilter">
    <!-- report all violations except ignore -->
    <property name="severity" value="ignore"/>
    <property name="acceptOnMatch" value="false"/>
  </module>
  <module name="SuppressWithPlainTextCommentFilter">
    <!--
      Use suppressions.xml for suppressions, this is only example.
      checkFormat will prevent suppression comments from being valid.
    -->
    <property name="checkFormat" value="IGNORETHIS"/>
    <property name="offCommentFormat" value="CSOFF\: .*"/>
    <property name="onCommentFormat" value="CSON\: .*"/>
  </module>

  <!-- Miscellaneous -->
  <module name="NewlineAtEndOfFile"/>
  <module name="Translation">
    <property name="requiredTranslations" value="de, fr, fi, es, pt, ja, tr, zh"/>
  </module>
  <module name="UniqueProperties"/>

  <!-- Regexp -->
  <module name="RegexpMultiline"/>
  <module name="RegexpMultiline">
    <property name="format" value="\r?\n[\t ]*\r?\n[\t ]*\r?\n"/>
    <property name="fileExtensions" value="java,xml,properties"/>
    <property name="message" value="Unnecessary consecutive lines"/>
  </module>
  <module name="RegexpMultiline">
      <property name="format" value="/\*\*\W+\* +\p{javaLowerCase}"/>
      <property name="fileExtensions" value="java"/>
      <property name="message"
                value="First sentence in a comment should start with a capital letter"/>
  </module>
  <module name="RegexpSingleline">
    <property name="format" value="\s+$"/>
    <property name="minimum" value="0"/>
    <property name="maximum" value="0"/>
  </module>
  <module name="RegexpSingleline">
      <property name="format" value="/\*\* +\p{javaLowerCase}"/>
      <property name="fileExtensions" value="java"/>
      <property name="message"
                value="First sentence in a comment should start with a capital letter"/>
  </module>
  <module name="RegexpSingleline">
    <property name="format" value="^(?!(.*http|import)).{101,}$"/>
    <property name="fileExtensions" value="g, g4"/>
    <property name="message" value="Line should not be longer than 100 symbols"/>
  </module>
  <module name="RegexpSingleline">
    <property name="format" value="^(?!(\s*&lt;a href=&quot;[^&quot;]+&quot;&gt;|.*http)).{101,}$"/>
    <property name="fileExtensions" value="xml, vm"/>
    <property name="message" value="Line should not be longer than 100 symbols"/>
  </module>
  <module name="RegexpSingleline">
    <property name="id" value="noSourceforgeNetLinks"/>
    <property name="format" value="checkstyle\.sourceforge\.net"/>
    <property name="message"
              value="Old site links should not be used, please use https://checkstyle.org"/>
  </module>
  <module name="RegexpSingleline">
    <property name="id" value="noSourceforgeIoLinks"/>
    <property name="format" value="checkstyle\.sourceforge\.io"/>
    <property name="message"
              value="Old site links should not be used, please use https://checkstyle.org"/>
  </module>
  <module name="RegexpOnFilename" />
  <module name="RegexpOnFilename">
      <property name="folderPattern" value="[\\/]src[\\/]\w+[\\/]java[\\/]"/>
      <property name="fileNamePattern" value="\.java$"/>
      <property name="match" value="false"/>
      <message key="regexp.filepath.mismatch"
               value="Only java files should be located in the ''src/*/java'' folders."/>
  </module>
  <module name="RegexpOnFilename">
      <property name="folderPattern" value="[\\/]src[\\/]xdocs[\\/]"/>
      <property name="fileNamePattern" value="\.(xml)|(vm)$"/>
      <property name="match" value="false"/>
      <message key="regexp.filepath.mismatch"
        value="All files in the ''src/xdocs'' folder should have the ''xml'' or ''vm'' extension."/>
  </module>
  <module name="RegexpOnFilename">
      <property name="folderPattern" value="[\\/]src[\\/]it[\\/]java[\\/]"/>
      <property name="fileNamePattern" value="^((\w+Test)|(\w+TestSupport)|(Abstract\w+))\.java$"/>
      <property name="match" value="false"/>
      <message key="regexp.filepath.mismatch"
               value="All files in the ''src/it/java'' folder
                      should be named ''*Test.java'' or ''Abstract*.java''."/>
  </module>

  <!-- Size Violations -->
  <module name="FileLength">
    <property name="fileExtensions" value="java"/>
  </module>

  <!-- Whitespace -->
  <module name="TreeWalker">
    <property name="tabWidth" value="4"/>

    <!-- Annotations -->
    <module name="AnnotationLocation">
      <property name="tokens" value="ANNOTATION_DEF"/>
      <property name="tokens" value="ANNOTATION_FIELD_DEF"/>
      <property name="tokens" value="PACKAGE_DEF"/>
      <property name="tokens" value="ENUM_CONSTANT_DEF"/>
      <property name="tokens" value="VARIABLE_DEF"/>
      <property name="allowSamelineSingleParameterlessAnnotation" value="false"/>
    </module>
    <module name="AnnotationOnSameLine">
      <!-- we can not use it as it conflicts with AnnotationLocation -->
      <property name="severity" value="ignore"/>
      <property name="tokens" value="METHOD_DEF"/>
      <property name="tokens" value="CTOR_DEF"/>
      <property name="tokens" value="TYPECAST"/>
      <property name="tokens" value="DOT"/>
      <property name="tokens" value="CLASS_DEF"/>
      <property name="tokens" value="ENUM_DEF"/>
      <property name="tokens" value="INTERFACE_DEF"/>
      <property name="tokens" value="TYPE_ARGUMENT"/>
      <property name="tokens" value="ANNOTATION_DEF"/>
      <property name="tokens" value="LITERAL_NEW"/>
      <property name="tokens" value="LITERAL_THROWS"/>
      <property name="tokens" value="VARIABLE_DEF"/>
      <property name="tokens" value="PARAMETER_DEF"/>
      <property name="tokens" value="IMPLEMENTS_CLAUSE"/>
      <property name="tokens" value="ANNOTATION_FIELD_DEF"/>
    </module>
    <module name="AnnotationUseStyle"/>
    <module name="MissingDeprecated"/>
    <module name="MissingOverride"/>
    <module name="PackageAnnotation"/>
    <module name="SuppressWarnings">
        <property name="format" value="^((?!unchecked|deprecation|rawtypes|resource).)*$"/>
        <message key="suppressed.warning.not.allowed"
             value="The warning ''{0}'' cannot be suppressed at this location.
             Only few javac warnings are allowed to suppress.
             If try to suppress checkstyle/pmd/..... violation please do this in their config file.
             If you try to suppress IntelliJ IDEA inspection,
             please use javadoc block tag @noinspection"
             />
    </module>
    <module name="SuppressWarningsHolder"/>

    <!-- Block Checks -->
    <module name="AvoidNestedBlocks">
      <property name="allowInSwitchCase" value="true"/>
    </module>
    <module name="NeedBraces"/>
    <module name="NeedBraces">
      <property name="tokens" value="LAMBDA"/>
      <property name="allowSingleLineStatement" value="true"/>
    </module>

    <!-- Class Design -->
    <module name="DesignForExtension">
      <property name="ignoredAnnotations"
                value="Override, Test, Before, After, BeforeClass, AfterClass"/>
    </module>
    <module name="FinalClass"/>
    <module name="HideUtilityClassConstructor"/>
    <module name="InnerTypeLast"/>
    <module name="InterfaceIsType"/>
    <module name="MutableException"/>
    <module name="OneTopLevelClass"/>
    <module name="ThrowsCount">
      <property name="max" value="2"/>
    </module>
    <module name="VisibilityModifier"/>

    <!-- Coding -->
    <module name="ArrayTrailingComma"/>
    <module name="AvoidInlineConditionals"/>
    <module name="CovariantEquals"/>
    <module name="DeclarationOrder"/>
    <module name="DefaultComesLast"/>
    <module name="EmptyStatement"/>
    <module name="EqualsAvoidNull"/>
    <module name="EqualsHashCode"/>
    <module name="ExplicitInitialization"/>
    <module name="FallThrough"/>
    <module name="FinalLocalVariable"/>
    <module name="HiddenField">
        <property name="ignoreConstructorParameter" value="true"/>
        <property name="ignoreSetter" value="true"/>
        <property name="setterCanReturnItsClass" value="true"/>
    </module>
    <module name="IllegalInstantiation">
        <property name="classes"
                  value="org.xml.sax.SAXException, org.xml.sax.SAXParseException,
                         org.apache.commons.beanutils.ConversionException,
                         org.antlr.v4.runtime.misc.ParseCancellationException,
                         antlr.RecognitionException, antlr.TokenStreamException,
                         antlr.TokenStreamRecognitionException, antlr.ANTLRException,
                         java.lang.StringBuffer"/>
    </module>
    <module name="IllegalThrows"/>
    <module name="IllegalToken">
        <property name="tokens" value="LABELED_STAT"/>
        <property name="tokens" value="LITERAL_NATIVE"/>
        <property name="tokens" value="LITERAL_VOLATILE"/>
        <property name="tokens" value="LITERAL_ASSERT"/>
    </module>
    <module name="IllegalTokenText">
      <property name="tokens" value="STRING_LITERAL"/>
      <property name="format" value="^(US-ASCII|ISO-8859-1|UTF-8|UTF-16BE|UTF-16LE|UTF-16)$"/>
      <property name="ignoreCase" value="true"/>
    </module>
    <module name="IllegalType">
      <property name="illegalClassNames"
                value="java.util.HashSet, HashSet, java.util.LinkedHashMap, LinkedHashMap,
                       java.util.TreeMap, TreeMap, java.util.HashMap, HashMap,
                       java.util.LinkedHashSet, LinkedHashSet, java.util.TreeSet, TreeSet,
                       java.lang.StringBuffer, StringBuffer"/>
    </module>
    <module name="InnerAssignment"/>
    <module name="MissingCtor">
      <!--
        we will not use that fanatic validation, extra code is not good
        But this Check will exists as it was created by community demand.
      -->
      <property name="severity" value="ignore"/>
    </module>
    <module name="MissingSwitchDefault"/>
    <module name="ModifiedControlVariable"/>
    <module name="MultipleVariableDeclarations"/>
    <module name="NestedForDepth">
      <property name="max" value="2"/>
    </module>
    <module name="NestedIfDepth">
      <property name="max" value="3"/>
    </module>
    <module name="NestedTryDepth"/>
    <module name="NoClone"/>
    <module name="NoFinalizer"/>
    <module name="OneStatementPerLine"/>
    <module name="OverloadMethodsDeclarationOrder"/>
    <module name="PackageDeclaration"/>
    <module name="ParameterAssignment"/>
    <module name="RequireThis"/>
    <module name="ReturnCount">
      <property name="max" value="1"/>
      <property name="maxForVoid" value="0"/>
    </module>
    <module name="SimplifyBooleanExpression"/>
    <module name="SimplifyBooleanReturn"/>
    <module name="StringLiteralEquality"/>
    <module name="SuperClone"/>
    <module name="SuperFinalize"/>
    <module name="UnnecessaryParentheses"/>
    <module name="VariableDeclarationUsageDistance"/>

    <!-- Filters-->
    <module name="SuppressionCommentFilter">
      <!--
        Use suppressions.xml for suppressions, this is only example.
        checkFormat will prevent suppression comments from being valid.
      -->
      <property name="checkFormat" value="IGNORETHIS"/>
      <property name="offCommentFormat" value="CSOFF\: .*"/>
      <property name="onCommentFormat" value="CSON\: .*"/>
    </module>
    <!-- Tone down the checking for test code -->
    <module name="SuppressionXpathSingleFilter">
      <property name="files" value="[\\/]internal[\\/].*[\\/]\w+Util\.java"/>
      <property name="checks" value="IllegalCatch"/>
    </module>
    <module name="SuppressionXpathSingleFilter">
      <property name="files" value=".*[\\/]src[\\/]test[\\/]"/>
      <property name="checks" value="EmptyBlock"/>
    </module>
    <module name="SuppressionXpathSingleFilter">
      <property name="files" value=".*[\\/]src[\\/](test|it)[\\/]"/>
      <property name="checks" value="JavadocVariable"/>
    </module>
    <module name="SuppressionXpathSingleFilter">
      <property name="files" value=".*[\\/]src[\\/](test|it)[\\/]"/>
      <property name="checks" value="JavadocType"/>
    </module>
    <module name="SuppressionXpathSingleFilter">
      <property name="files" value=".*[\\/]src[\\/](test|it)[\\/]"/>
      <property name="checks" value="MagicNumber"/>
    </module>
    <module name="SuppressionXpathSingleFilter">
      <property name="files" value=".*[\\/]src[\\/](test|it)[\\/]"/>
      <property name="checks" value="AvoidStaticImport"/>
    </module>
    <module name="SuppressionXpathSingleFilter">
      <property name="files" value=".*[\\/]src[\\/](test|it)[\\/]"/>
      <property name="checks" value="WriteTag"/>
    </module>
    <module name="SuppressionXpathSingleFilter">
      <property name="files" value=".*[\\/]src[\\/](test|it)[\\/]"/>
      <property name="checks" value="MethodCount"/>
    </module>
    <!-- Fixing these cases will decrease code readability -->
    <module name="SuppressionXpathSingleFilter">
      <property name="files" value=".*[\\/]src[\\/](test|it)[\\/]"/>
      <property name="checks" value="MultipleStringLiterals"/>
    </module>
    <module name="SuppressWithNearbyCommentFilter">
      <property name="commentFormat"
                value="-@cs\[(\w{8,}(\|\w{8,})*)\] \w[\(\)\-\.\'\`\,\:\;\w ]{10,}"/>
      <property name="checkFormat" value="$1"/>
      <property name="influenceFormat" value="3"/>
    </module>

    <!-- Imports -->
    <module name="AvoidStarImport"/>
    <module name="AvoidStaticImport"/>
    <module name="CustomImportOrder">
      <property name="customImportOrderRules"
                value="STATIC###STANDARD_JAVA_PACKAGE###SPECIAL_IMPORTS"/>
      <property name="specialImportsRegExp" value="^org\."/>
      <property name="sortImportsInGroupAlphabetically" value="true"/>
      <property name="separateLineBetweenGroups" value="true"/>
    </module>
    <module name="IllegalImport"/>
    <module name="ImportOrder">
      <property name="groups" value="/^java\./,javax,org"/>
      <property name="ordered" value="true"/>
      <property name="separated" value="true"/>
      <property name="option" value="top"/>
      <property name="sortStaticImportsAlphabetically" value="true"/>
    </module>
    <module name="RedundantImport"/>
    <module name="UnusedImports"/>

    <!-- Metrics -->
    <module name="BooleanExpressionComplexity">
      <property name="max" value="7"/>
    </module>
    <module name="ClassDataAbstractionCoupling">
        <!-- Default classes are also listed-->
        <property name="excludedClasses"
                  value="boolean, byte, char, double, float, int, long, short, void,
                         Boolean, Byte, Character, Double, Float, Integer, Long, Short, Void,
                         Object, Class, String, StringBuffer, StringBuilder,
                         ArrayIndexOutOfBoundsException, Exception, RuntimeException,
                         IllegalArgumentException, IllegalStateException,
                         IndexOutOfBoundsException, NullPointerException, Throwable,
                         SecurityException, UnsupportedOperationException, List, ArrayList,
                         Deque, Queue, LinkedList, Set, HashSet, SortedSet, TreeSet, Map,
                         HashMap, SortedMap, TreeMap, DetailsAST,
                         UnsupportedEncodingException, BuildException, ConversionException,
                         FileNotFoundException, TestException"/>
    </module>
    <module name="NPathComplexity"/>

    <!-- Misc -->
    <module name="ArrayTypeStyle"/>
    <module name="AvoidEscapedUnicodeCharacters">
      <property name="allowIfAllCharactersEscaped" value="true"/>
    </module>
    <module name="CommentsIndentation"/>
    <module name="DescendantToken"/>
    <module name="FinalParameters">
      <!--
        we will not use that fanatic validation, extra modifiers pollute a code
        it is better to use extra validation(Check) that argument is reassigned
        But this Check will exists as it was created by community demand.
      -->
      <property name="severity" value="ignore"/>
    </module>
    <module name="Indentation">
      <property name="basicOffset" value="4"/>
      <property name="braceAdjustment" value="0"/>
      <property name="caseIndent" value="4"/>
      <property name="throwsIndent" value="8"/>
    </module>
    <module name="OuterTypeFilename"/>
    <module name="TodoComment">
      <property name="format" value="(TODO)|(FIXME)" />
    </module>
    <module name="TrailingComment"/>
    <module name="UncommentedMain">
      <property name="excludedClasses" value="\.(Main|JavadocPropertiesGenerator)$"/>
    </module>
    <module name="UpperEll"/>

    <!-- Modifiers -->
    <module name="ClassMemberImpliedModifier">
      <!-- effectively the opposite of RedundantModifier, so output must be ignored -->
      <property name="severity" value="ignore"/>
    </module>
    <module name="InterfaceMemberImpliedModifier">
      <!-- effectively the opposite of RedundantModifier, so output must be ignored -->
      <property name="severity" value="ignore"/>
    </module>
    <module name="ModifierOrder"/>
    <module name="RedundantModifier"/>

    <!-- Naming Conventions -->
    <module name="AbstractClassName"/>
    <module name="ClassTypeParameterName"/>
    <module name="ConstantName"/>
    <module name="InterfaceTypeParameterName"/>
    <module name="LocalFinalVariableName"/>
    <module name="LocalVariableName">
      <property name="format" value="^(id)|([a-z][a-z0-9][a-zA-Z0-9]+)$"/>
      <property name="allowOneCharVarInForLoop" value="true"/>
    </module>
    <module name="MemberName">
      <property name="format" value="^(id)|([a-z][a-z0-9][a-zA-Z0-9]+)$"/>
    </module>
    <module name="MethodName"/>
    <module name="MethodTypeParameterName"/>
    <module name="PackageName"/>
    <module name="ParameterName">
      <property name="format" value="^(id)|([a-z][a-z0-9][a-zA-Z0-9]+)$"/>
      <property name="ignoreOverridden" value="true"/>
    </module>
    <module name="LambdaParameterName">
      <property name="format" value="^(id)|([a-z][a-z0-9][a-zA-Z0-9]+)$"/>
    </module>
    <module name="CatchParameterName">
      <property name="format" value="^(ex|[a-z][a-z][a-zA-Z]+)$"/>
    </module>
    <module name="StaticVariableName">
      <property name="format" value="^(id)|([a-z][a-z0-9][a-zA-Z0-9]+)$"/>
    </module>
    <module name="TypeName"/>

    <!-- Regexp -->
    <module name="Regexp"/>
    <module name="RegexpSinglelineJava"/>
    <module name="RegexpSinglelineJava">
      <property name="format" value="[^\p{ASCII}]"/>
      <property name="ignoreComments" value="true"/>
    </module>

    <!-- Size Violations -->
    <module name="AnonInnerLength"/>
    <module name="ExecutableStatementCount">
        <property name="max" value="30"/>
    </module>
    <module name="MethodCount">
      <property name="maxTotal" value="34"/>
    </module>
    <module name="MethodLength"/>
    <module name="OuterTypeNumber"/>
    <module name="ParameterNumber"/>

    <!-- Whitespace -->
    <module name="EmptyForInitializerPad"/>
    <module name="EmptyForIteratorPad"/>
    <module name="EmptyLineSeparator">
      <property name="allowNoEmptyLineBetweenFields" value="true"/>
      <property name="allowMultipleEmptyLinesInsideClassMembers" value="false"/>
    </module>
    <module name="GenericWhitespace"/>
    <module name="MethodParamPad"/>
    <module name="NoLineWrap"/>
    <module name="NoWhitespaceAfter">
      <property name="tokens" value="ARRAY_INIT"/>
      <property name="tokens" value="AT"/>
      <property name="tokens" value="BNOT"/>
      <property name="tokens" value="DEC"/>
      <property name="tokens" value="DOT"/>
      <property name="tokens" value="INC"/>
      <property name="tokens" value="LNOT"/>
      <property name="tokens" value="UNARY_MINUS"/>
      <property name="tokens" value="UNARY_PLUS"/>
      <property name="tokens" value="ARRAY_DECLARATOR"/>
      <property name="tokens" value="INDEX_OP"/>
      <property name="tokens" value="METHOD_REF"/>
    </module>
    <module name="NoWhitespaceBefore"/>
    <module name="NoWhitespaceBefore">
      <property name="tokens" value="DOT"/>
      <property name="tokens" value="METHOD_REF"/>
      <property name="allowLineBreaks" value="true"/>
    </module>
    <module name="ParenPad"/>
    <module name="SeparatorWrap">
      <property name="tokens" value="DOT"/>
      <property name="tokens" value="AT"/>
      <property name="tokens" value="METHOD_REF"/>
      <property name="option" value="nl"/>
    </module>
    <module name="SingleSpaceSeparator">
      <property name="validateComments" value="false"/>
    </module>
    <module name="TypecastParenPad"/>
    <module name="WhitespaceAfter"/>
    <module name="WhitespaceAround"/>

  </module>

</module>