Custom set of Checkstyle Rules. Using Google ruleset as base.

checkstyle.xml

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

<!--
  Checkstyle configuration that checks the sun coding conventions from:
    - the Java Language Specification at
      https://docs.oracle.com/javase/specs/jls/se11/html/index.html
    - the Sun Code Conventions at https://www.oracle.com/technetwork/java/codeconvtoc-136057.html
    - the Javadoc guidelines at
      https://www.oracle.com/technetwork/java/javase/documentation/index-137868.html
    - the JDK Api documentation https://docs.oracle.com/en/java/javase/11/
    - some best practices
  Checkstyle is very configurable. Be sure to read the documentation at
  http://checkstyle.sourceforge.net (or in your downloaded distribution).
  Most Checks are configurable, be sure to consult the documentation.
  To completely disable a check, just comment it out or delete it from the file.
  Finally, it is worth reading the documentation.
-->

<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/5.x/config.html#Checker
      <property name="basedir" value="${basedir}"/>
  -->

  <property name="charset" value="UTF-8"/>

  <module name="SuppressionFilter">
    <property name="file" value="${config_loc}/suppressions.xml"/>
  </module>

  <module name="SuppressWarningsFilter"/>

  <property name="fileExtensions" value="java, properties, xml"/>

  <!-- Excludes all 'module-info.java' files              -->
  <!-- See https://checkstyle.org/config_filefilters.html -->
  <module name="BeforeExecutionExclusionFileFilter">
    <property name="fileNamePattern" value="module\-info\.java$"/>
  </module>

  <!-- Checks that a package-info.java file exists for each package.     -->
  <!-- See http://checkstyle.sourceforge.net/config_javadoc.html#JavadocPackage -->
  <!-- <module name="JavadocPackage"/> -->

  <!-- Checks whether files end with a new line.                        -->
  <!-- See http://checkstyle.sourceforge.net/config_misc.html#NewlineAtEndOfFile -->
  <module name="NewlineAtEndOfFile"/>

  <!-- Checks that property files contain the same keys.         -->
  <!-- See http://checkstyle.sourceforge.net/config_misc.html#Translation -->
  <module name="Translation"/>

  <!-- Checks for Size Violations.                    -->
  <!-- See http://checkstyle.sourceforge.net/config_sizes.html -->
  <module name="FileLength"/>
  <module name="LineLength">
    <property name="max" value="120"/>
    <property name="ignorePattern" value="^package.*|^import.*|a href|href|http://|https://|ftp://"/>
  </module>
  <!-- Checks for whitespace                               -->
  <!-- See http://checkstyle.sourceforge.net/config_whitespace.html -->
  <module name="FileTabCharacter">
    <property name="eachLine" value="true"/>
  </module>

  <!-- Miscellaneous other checks.                   -->
  <!-- See http://checkstyle.sourceforge.net/config_misc.html -->
  <module name="RegexpSingleline">
    <property name="format" value="\s+$"/>
    <property name="minimum" value="0"/>
    <property name="maximum" value="0"/>
    <property name="message" value="Line has trailing spaces."/>
  </module>

  <module name="UniqueProperties">
    <property name="fileExtensions" value="properties"/>
  </module>

  <!-- Checks for Headers                                -->
  <!-- See http://checkstyle.sourceforge.net/config_header.html   -->
  <!-- <module name="Header"> -->
  <!--   <property name="headerFile" value="${checkstyle.header.file}"/> -->
  <!--   <property name="fileExtensions" value="java"/> -->
  <!-- </module> -->

  <module name="TreeWalker">
    <module name="SuppressWarningsHolder"/>

    <!-- Checks for Javadoc comments.                     -->
    <!-- See http://checkstyle.sourceforge.net/config_javadoc.html -->
    <module name="NonEmptyAtclauseDescription"/>
    <module name="InvalidJavadocPosition"/>
    <module name="JavadocTagContinuationIndentation"/>
    <module name="SummaryJavadoc">
      <property name="forbiddenSummaryFragments"
        value="^@return the *|^This method returns |^A [{]@code [a-zA-Z0-9]+[}]( is a )"/>
    </module>
    <module name="JavadocParagraph"/>
    <module name="AtclauseOrder">
      <property name="tagOrder" value="@param, @return, @throws, @deprecated"/>
      <property name="target" value="CLASS_DEF, INTERFACE_DEF, ENUM_DEF, METHOD_DEF, CTOR_DEF, VARIABLE_DEF"/>
    </module>
    <module name="JavadocMethod">
      <property name="scope" value="public"/>
      <property name="allowMissingParamTags" value="true"/>
      <property name="allowMissingReturnTag" value="true"/>
      <property name="allowedAnnotations" value="Override, Test"/>
    </module>
    <module name="MissingJavadocMethod">
      <property name="scope" value="public"/>
      <property name="minLineCount" value="2"/>
      <property name="allowedAnnotations" value="Override, Test"/>
    </module>
    <module name="SingleLineJavadoc">
      <property name="ignoreInlineTags" value="false"/>
    </module>
    <!--
    <module name="JavadocType"/>
    <module name="JavadocVariable"/>
    <module name="JavadocStyle"/>
    <module name="JavadocStyle">
         <property name="checkEmptyJavadoc" value="true"/>
    </module> -->

    <module name="EmptyCatchBlock">
      <property name="exceptionVariableName" value="expected"/>
    </module>

    <!-- Checks for Naming Conventions.                  -->
    <!-- See http://checkstyle.sourceforge.net/config_naming.html -->
    <module name="ConstantName"/>
    <module name="LocalVariableName">
      <property name="tokens" value="VARIABLE_DEF"/>
      <property name="format" value="^[a-z]([a-z0-9][a-zA-Z0-9]*)?$"/>
      <message key="name.invalidPattern" value="Local variable name ''{0}'' must match pattern ''{1}''."/>
    </module>
    <module name="MemberName">
      <property name="format" value="^[a-z][a-z0-9][a-zA-Z0-9]*$"/>
      <message key="name.invalidPattern" value="Member name ''{0}'' must match pattern ''{1}''."/>
    </module>
    <module name="MethodName">
      <property name="format" value="^[a-z][a-z0-9][a-zA-Z0-9_]*$"/>
      <message key="name.invalidPattern" value="Method name ''{0}'' must match pattern ''{1}''."/>
    </module>
    <module name="PackageName">
      <property name="format" value="^[a-z]+(\.[a-z][a-z0-9]*)*$"/>
      <message key="name.invalidPattern" value="Package name ''{0}'' must match pattern ''{1}''."/>
    </module>
    <module name="ParameterName">
      <property name="format" value="^[a-z]([a-z0-9][a-zA-Z0-9]*)?$"/>
      <message key="name.invalidPattern" value="Parameter name ''{0}'' must match pattern ''{1}''."/>
    </module>
    <module name="StaticVariableName"/>
    <module name="TypeName">
      <message key="name.invalidPattern" value="Type name ''{0}'' must match pattern ''{1}''."/>
    </module>

    <module name="OneTopLevelClass"/>
    <module name="NoLineWrap"/>

    <!-- Checks for imports                              -->
    <!-- See http://checkstyle.sourceforge.net/config_import.html -->
    <module name="AvoidStarImport"/>
    <module name="IllegalImport"/> <!-- defaults to sun.* packages -->
    <module name="RedundantImport"/>
    <module name="UnusedImports">
      <property name="processJavadoc" value="false"/>
    </module>

    <!-- Checks for Size Violations.                    -->
    <!-- See http://checkstyle.sourceforge.net/config_sizes.html -->
    <module name="MethodLength">
      <property name="max" value="50"/>
    </module>
    <module name="ParameterNumber">
      <property name="tokens" value="METHOD_DEF"/>
    </module>

    <!-- Checks for whitespace                               -->
    <!-- See http://checkstyle.sourceforge.net/config_whitespace.html -->
    <module name="EmptyForInitializerPad"/>
    <module name="EmptyForIteratorPad"/>
    <module name="GenericWhitespace"/>
    <module name="MethodParamPad"/>
    <module name="NoWhitespaceAfter"/>
    <module name="NoWhitespaceBefore">
      <property name="tokens" value="COMMA, SEMI, POST_INC, POST_DEC, DOT, ELLIPSIS, METHOD_REF"/>
      <property name="allowLineBreaks" value="true"/>
    </module>
    <module name="OperatorWrap">
      <property name="option" value="NL"/>
      <property name="tokens"
        value="BAND, BOR, BSR, BXOR, DIV, EQUAL, GE, GT, LAND, LE, LITERAL_INSTANCEOF, LOR,
                    LT, MINUS, MOD, NOT_EQUAL, PLUS, QUESTION, SL, SR, STAR, METHOD_REF "/>
    </module>
    <module name="ParenPad"/>
    <module name="TypecastParenPad"/>
    <module name="WhitespaceAfter"/>
    <module name="WhitespaceAround">
      <message key="ws.notFollowed"
        value="WhitespaceAround: ''{0}'' is not followed by whitespace. Empty blocks may only be represented as '{}' when not part of a multi-block statement (4.1.3)"/>
      <message key="ws.notPreceded"
        value="WhitespaceAround: ''{0}'' is not preceded with whitespace."/>
      <property name="allowEmptyMethods" value="true"/>
      <property name="allowEmptyTypes" value="true"/>
      <property name="allowEmptyLoops" value="true"/>
      <property name="tokens"
        value="ASSIGN, BAND, BAND_ASSIGN, BOR, BOR_ASSIGN, BSR, BSR_ASSIGN, BXOR,
                    BXOR_ASSIGN, COLON, DIV, DIV_ASSIGN, DO_WHILE, EQUAL, GE, GT, LAMBDA, LAND,
                    LCURLY, LE, LITERAL_CATCH, LITERAL_DO, LITERAL_ELSE, LITERAL_FINALLY,
                    LITERAL_FOR, LITERAL_IF, LITERAL_RETURN, LITERAL_SWITCH, LITERAL_SYNCHRONIZED,
                     LITERAL_TRY, LITERAL_WHILE, LOR, LT, MINUS, MINUS_ASSIGN, MOD, MOD_ASSIGN,
                     NOT_EQUAL, PLUS, PLUS_ASSIGN, QUESTION, RCURLY, SL, SLIST, SL_ASSIGN, SR,
                     SR_ASSIGN, STAR, STAR_ASSIGN, LITERAL_ASSERT, TYPE_EXTENSION_AND"/>
      <property name="allowEmptyConstructors" value="true"/>
      <property name="allowEmptyLambdas" value="true"/>
    </module>
    <module name="EmptyLineSeparator">
      <property name="allowNoEmptyLineBetweenFields" value="true"/>
      <property name="allowMultipleEmptyLinesInsideClassMembers" value="false"/>
    </module>
    <module name="SingleSpaceSeparator"/>

    <!-- Modifier Checks                                    -->
    <!-- See http://checkstyle.sourceforge.net/config_modifiers.html -->
    <module name="ModifierOrder"/>
    <module name="RedundantModifier"/>

    <!-- Checks for blocks. You know, those {}'s         -->
    <!-- See http://checkstyle.sourceforge.net/config_blocks.html -->
    <module name="AvoidNestedBlocks"/>
    <module name="EmptyBlock"/>
    <module name="LeftCurly"/>
    <module name="NeedBraces"/>
    <module name="RightCurly"/>

    <!-- Checks for common coding problems               -->
    <!-- See http://checkstyle.sourceforge.net/config_coding.html -->
    <module name="EmptyStatement"/>
    <module name="EqualsHashCode"/>
    <module name="HiddenField">
      <property name="tokens" value="VARIABLE_DEF"/>
    </module>
    <module name="IllegalInstantiation"/>
    <module name="InnerAssignment"/>
    <module name="MagicNumber"/>
    <module name="MissingSwitchDefault"/>
    <module name="SimplifyBooleanExpression"/>
    <module name="SimplifyBooleanReturn"/>
    <module name="CovariantEquals"/>
    <module name="DeclarationOrder"/>
    <module name="DefaultComesLast"/>
    <module name="EqualsAvoidNull"/>
    <module name="ExplicitInitialization"/>
    <module name="FinalLocalVariable"/>
    <module name="IllegalCatch"/>
    <module name="IllegalThrows"/>
    <module name="ModifiedControlVariable">
      <property name="skipEnhancedForLoopVariable" value="true"/>
    </module>
    <module name="MultipleStringLiterals"/>
    <module name="MultipleVariableDeclarations"/>
    <module name="NestedIfDepth">
      <property name="max" value="2"/>
    </module>
    <module name="NestedForDepth">
      <property name="max" value="2"/>
    </module>
    <module name="NestedTryDepth">
      <property name="max" value="3"/>
    </module>
    <module name="NoClone"/>
    <module name="NoFinalizer"/>
    <module name="OneStatementPerLine"/>
    <module name="OverloadMethodsDeclarationOrder"/>
    <module name="ParameterAssignment"/>
    <module name="ReturnCount">
      <property name="max" value="3"/>
      <property name="maxForVoid" value="1"/>
    </module>
    <module name="SimplifyBooleanExpression"/>
    <module name="SimplifyBooleanReturn"/>
    <module name="StringLiteralEquality"/>
    <module name="UnnecessaryParentheses"/>
    <module name="VariableDeclarationUsageDistance"/>

    <module name="FallThrough"/>

    <!-- Checks for class design                         -->
    <!-- See http://checkstyle.sourceforge.net/config_design.html -->
    <!--
    <module name="DesignForExtension"/>
    <module name="HideUtilityClassConstructor"/>
    -->
    <module name="FinalClass"/>
    <module name="InterfaceIsType"/>
    <!-- <module name="VisibilityModifier"/> -->
    <module name="MutableException"/>
    <module name="ThrowsCount">
      <property name="max" value="5"/>
    </module>

    <!-- Miscellaneous other checks.                   -->
    <!-- See http://checkstyle.sourceforge.net/config_misc.html -->
    <module name="ArrayTypeStyle"/>
    <module name="FinalParameters"/>
    <!--
    <module name="TodoComment"/>
    -->
    <module name="UpperEll"/>
    <module name="CommentsIndentation"/>
    <module name="Indentation">
      <property name="basicOffset" value="2"/>
      <property name="braceAdjustment" value="0"/>
      <property name="caseIndent" value="2"/>
      <property name="throwsIndent" value="4"/>
      <property name="lineWrappingIndentation" value="4"/>
      <property name="arrayInitIndent" value="2"/>
    </module>
    <module name="OuterTypeFilename"/>
    <module name="IllegalTokenText">
      <property name="tokens" value="STRING_LITERAL, CHAR_LITERAL"/>
      <property name="format"
        value="\\u00(09|0(a|A)|0(c|C)|0(d|D)|22|27|5(C|c))|\\(0(10|11|12|14|15|42|47)|134)"/>
      <property name="message"
        value="Consider using special escape sequence instead of octal value or Unicode escaped value."/>
    </module>
    <module name="AvoidEscapedUnicodeCharacters">
      <property name="allowEscapesForControlCharacters" value="true"/>
      <property name="allowByTailComment" value="true"/>
      <property name="allowNonPrintableEscapes" value="true"/>
    </module>
    <module name="TrailingComment"/>

    <module name="AnnotationLocation">
      <property name="id" value="AnnotationLocationMostCases"/>
      <property name="tokens" value="CLASS_DEF, INTERFACE_DEF, ENUM_DEF, METHOD_DEF, CTOR_DEF"/>
    </module>
    <module name="AnnotationLocation">
      <property name="id" value="AnnotationLocationVariables"/>
      <property name="tokens" value="VARIABLE_DEF"/>
      <property name="allowSamelineMultipleAnnotations" value="true"/>
    </module>
    <module name="AnnotationUseStyle"/>

    <module name="MissingDeprecated"/>
    <module name="MissingOverride"/>
    <module name="SuppressWarnings"/>
    <module name="CyclomaticComplexity"/>
    <module name="JavaNCSS">
      <property name="methodMaximum" value="60"/>
    </module>
    <module name="AbbreviationAsWordInName">
      <property name="ignoreFinal" value="false"/>
      <property name="allowedAbbreviationLength" value="1"/>
    </module>
    <module name="CatchParameterName">
      <property name="format" value="^[a-z]([a-z0-9][a-zA-Z0-9]*)?$"/>
      <message key="name.invalidPattern" value="Catch parameter name ''{0}'' must match pattern ''{1}''."/>
    </module>
    <module name="ClassTypeParameterName">
      <property name="format" value="(^[A-Z][0-9]?)$|([A-Z][a-zA-Z0-9]*[T]$)"/>
      <message key="name.invalidPattern" value="Class type name ''{0}'' must match pattern ''{1}''."/>
    </module>
    <module name="MethodTypeParameterName">
      <property name="format" value="(^[A-Z][0-9]?)$|([A-Z][a-zA-Z0-9]*[T]$)"/>
      <message key="name.invalidPattern" value="Method type name ''{0}'' must match pattern ''{1}''."/>
    </module>
    <module name="LambdaParameterName">
      <property name="format" value="^[a-z]([a-z0-9][a-zA-Z0-9]*)?$"/>
      <message key="name.invalidPattern" value="Lambda parameter name ''{0}'' must match pattern ''{1}''."/>
    </module>
    <module name="InterfaceTypeParameterName">
      <property name="format" value="(^[A-Z][0-9]?)$|([A-Z][a-zA-Z0-9]*[T]$)"/>
      <message key="name.invalidPattern" value="Interface type name ''{0}'' must match pattern ''{1}''."/>
    </module>

    <module name="SeparatorWrap">
      <property name="id" value="SeparatorWrapDot"/>
      <property name="tokens" value="DOT"/>
      <property name="option" value="nl"/>
    </module>
    <module name="SeparatorWrap">
      <property name="id" value="SeparatorWrapComma"/>
      <property name="tokens" value="COMMA"/>
      <property name="option" value="EOL"/>
    </module>
    <module name="SeparatorWrap">
      <!-- ELLIPSIS is EOL until https://github.com/google/styleguide/issues/258 -->
      <property name="id" value="SeparatorWrapEllipsis"/>
      <property name="tokens" value="ELLIPSIS"/>
      <property name="option" value="EOL"/>
    </module>
    <module name="SeparatorWrap">
      <!-- ARRAY_DECLARATOR is EOL until https://github.com/google/styleguide/issues/259 -->
      <property name="id" value="SeparatorWrapArrayDeclarator"/>
      <property name="tokens" value="ARRAY_DECLARATOR"/>
      <property name="option" value="EOL"/>
    </module>
    <module name="SeparatorWrap">
      <property name="id" value="SeparatorWrapMethodRef"/>
      <property name="tokens" value="METHOD_REF"/>
      <property name="option" value="nl"/>
    </module>

  </module>

</module>