src/conf/checkstyle/checkstyle.xml

<?xml version="1.0"?>
<!--
 Licensed to the Apache Software Foundation (ASF) under one or more
 contributor license agreements.  See the NOTICE file distributed with
 this work for additional information regarding copyright ownership.
 The ASF licenses this file to You under the Apache License, Version 2.0
 (the "License"); you may not use this file except in compliance with
 the License.  You may obtain a copy of the License at

      https://www.apache.org/licenses/LICENSE-2.0

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 distributed under the License is distributed on an "AS IS" BASIS,
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 See the License for the specific language governing permissions and
 limitations under the License.
-->
<!DOCTYPE module PUBLIC
    "-//Checkstyle//DTD Checkstyle Configuration 1.3//EN"
    "https://checkstyle.org/dtds/configuration_1_3.dtd">
<module name="Checker">
  <property name="localeLanguage" value="en" />
  <module name="FileTabCharacter" />
  <module name="JavadocPackage" />
  <module name="RegexpSingleline">
    <property name="format" value="((public)|(protected))\s+void\s+finalize\(\s*\)" />
    <property name="message" value="Avoid finalizers." />
  </module>
  <module name="RegexpSingleline">
    <property name="format" value="^\s+\*\s+@author\s" />
    <property name="message" value="Deprecated @author tag" />
    <property name="fileExtensions" value="java" />
    <property name="severity" value="warning" />
  </module>
  <module name="RegexpSingleline">
    <property name="format" value="\s+$" />
    <property name="message" value="Line has trailing spaces." />
  </module>
  <module name="SuppressionFilter">
    <property name="file" value="src/conf/checkstyle/checkstyle-suppressions.xml" />
  </module>
  <module name="TreeWalker">
    <module name="AvoidStarImport" />
    <module name="ConstantName" />
    <module name="EmptyBlock">
      <property name="tokens" value="LITERAL_CATCH" />
      <!-- require a comment, change to stmt to require a statement -->
      <property name="option" value="text" />
    </module>
    <module name="EqualsHashCode" />
    <module name="ExplicitInitializationCheck" />
    <module name="FinalLocalVariable" />
    <module name="IllegalImport" />
    <module name="IllegalInstantiation">
      <property name="classes" value="java.lang.Boolean, java.lang.String" />
    </module>
    <module name="InterfaceIsType" />
    <module name="JavadocType">
      <property name="scope" value="protected" />
    </module>
    <module name="JavadocMethod">
      <property name="accessModifiers" value="protected" />
    </module>
    <module name="ImportOrder">
      <property name="option" value="top"/>
      <property name="groups" value="java,javax,org,junit"/>
      <property name="ordered" value="true"/>
      <property name="separated" value="true"/>
    </module>
    <module name="LeftCurly" />
    <module name="LocalFinalVariableName" />
    <module name="LocalVariableName" />
    <module name="MagicNumber" />
    <module name="MemberName" />
    <module name="MethodName" />
    <module name="MissingOverride" />
    <module name="ModifierOrder" />
    <module name="NeedBraces" />
    <module name="ParameterNumber">
      <property name="max" value="4" />
    </module>
    <module name="PackageName">
      <!-- no uppercase letters, between 2 and 10 characters -->
      <property name="format" value="^[a-z]+(\.[a-z][a-z0-9]{1,9})*$" />
    </module>
    <module name="ParameterName" />
    <module name="ParenPad" />
    <module name="RedundantImport" />
    <module name="RedundantModifier" />
    <module name="RightCurly" />
    <module name="SingleSpaceSeparator"/>
    <module name="StaticVariableName" />
    <module name="SuppressionCommentFilter" />
    <!-- Allow comment to suppress checkstyle for a single line e.g. // CHECKSTYLE IGNORE MagicNumber -->
    <module name="SuppressWithNearbyCommentFilter">
      <property name="commentFormat" value="CHECKSTYLE IGNORE (\w+)" />
      <property name="checkFormat" value="$1" />
    </module>
    <module name="TypecastParenPad"/>
    <module name="TypeName" />
    <module name="UnusedImports" />
    <module name="UpperEll" />
    <module name="WhitespaceAfter"/>
    <module name="WhitespaceAround"/>
  </module>
</module>