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">
    <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"/>

    <module name="NewlineAtEndOfFile"/>

    <!-- disallow trailing whitespace -->
    <module name="RegexpSingleline">
        <property name="format" value="\s+$"/>
        <property name="message" value="trailing whitespace"/>
    </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="SeparatorWrap">
            <property name="tokens" value="DOT,ELLIPSIS,AT"/>
            <property name="option" value="nl"/>
        </module>
        <module name="SeparatorWrap">
            <property name="tokens" value="COMMA,SEMI"/>
            <property name="option" value="eol"/>
        </module>

        <module name="ParenPad"/>
        <module name="NoWhitespaceBefore"/>
        <module name="NoWhitespaceAfter">
            <!-- allow ARRAY_INIT -->
            <property name="tokens" value="AT,INC,DEC,UNARY_MINUS,UNARY_PLUS,BNOT,LNOT,DOT,ARRAY_DECLARATOR,INDEX_OP"/>
        </module>
        <module name="WhitespaceAfter"/>
        <module name="WhitespaceAround">
            <!-- Allow PLUS, MINUS, STAR, DIV as they may be more readable without spaces in some cases -->
            <property name="tokens" value="ASSIGN,BAND,BAND_ASSIGN,BOR,BOR_ASSIGN,BSR,BSR_ASSIGN,BXOR,BXOR_ASSIGN,COLON,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_ASSIGN,MOD,MOD_ASSIGN,NOT_EQUAL,PLUS_ASSIGN,QUESTION,RCURLY,SL,SLIST,SL_ASSIGN,SR,SR_ASSIGN,STAR_ASSIGN,LITERAL_ASSERT,TYPE_EXTENSION_AND"/>
            <property name="allowEmptyCatches" value="true"/>
            <property name="allowEmptyConstructors" value="true"/>
            <property name="allowEmptyLambdas" value="true"/>
            <property name="allowEmptyLoops" value="true"/>
            <property name="allowEmptyMethods" value="true"/>
            <property name="allowEmptySwitchBlockStatements" value="true"/>
            <property name="allowEmptyTypes" value="true"/>
        </module>
        <module name="GenericWhitespace"/>

        <module name="ArrayTypeStyle"/>
        <module name="DefaultComesLast">
            <property name="skipIfLastAndSharedWithCase" value="true"/>
        </module>
        <module name="SimplifyBooleanExpression"/>
        <module name="SimplifyBooleanReturn"/>
        <module name="StringLiteralEquality"/>
        <module name="EqualsHashCode"/>

        <module name="HexLiteralCase"/>
        <module name="UpperEll"/>

        <module name="ModifierOrder"/>
        <module name="RedundantModifier"/>

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

        <!-- Enforce tabs -->
        <!-- TODO: enforce tabs in the future -->
        <!--<module name="RegexpSinglelineJava">-->
            <!--<property name="format" value="^\t* ([^*]|\*[^ /])"/>-->
            <!--<property name="message" value="non-tab indentation"/>-->
        <!--</module>-->

        <module name="OuterTypeFilename"/>
        <module name="PackageDeclaration"/>

        <module name="InvalidJavadocPosition"/>
        <module name="AtclauseOrder"/>

        <!-- Prevent non-@Unique fields in Mixin classes -->
        <module name="MatchXpath">
            <property name="query" value="
                //OBJBLOCK/VARIABLE_DEF[
                    not(
                        ./MODIFIERS/ANNOTATION/IDENT[
                            @text='Unique'
                            or @text='Shadow'
                        ]
                    )
                    and
                    ../../../CLASS_DEF[
                        ./MODIFIERS/ANNOTATION/IDENT[@text='Mixin']
                    ]
                ]
            "/>
            <message key="matchxpath.match" value="Mixin fields must be annotated with @Unique or @Shadow"/>
        </module>

        <!-- Prevent non-@Unique methods in Mixin classes -->
        <!-- All Mixin and MixinExtras annotations must be listed here -->
        <module name="MatchXpath">
            <property name="query" value="
                //METHOD_DEF[
                    not(
                        ./MODIFIERS/ANNOTATION/IDENT[
                            @text='Unique'
                            or @text='Inject'
                            or @text='ModifyArg'
                            or @text='ModifyExpressionValue'
                            or @text='ModifyReturnValue'
                            or @text='ModifyVariable'
                            or @text='Override'
                            or @text='Overwrite'
                            or @text='Redirect'
                            or @text='Shadow'
                            or @text='WrapMethod'
                            or @text='WrapOperation'
                            or @text='WrapWithCondition'
                        ]
                    )
                    and
                    ../../../CLASS_DEF[
                        ./MODIFIERS/ANNOTATION/IDENT[@text='Mixin']
                    ]
                ]
            "/>
            <message key="matchxpath.match" value="Mixin methods must be annotated with @Unique or one of the Mixin annotations"/>
        </module>

        <!-- Prevent @Inject local capture, @Local is preferred -->
        <module name="MatchXpath">
            <property name="query" value="
                //METHOD_DEF[
                    ./MODIFIERS/ANNOTATION[
                        ./IDENT[@text='Inject']
                        and
                        ./ANNOTATION_MEMBER_VALUE_PAIR/IDENT[@text='locals']
                    ]
                ]
            "/>
            <message key="matchxpath.match" value="Inject local capture is not allowed, use @Local instead"/>
        </module>

        <!-- Prevent String#toLowerCase/toUpperCase without a given Locale to prevent localization issues -->
        <!-- Not specifying a locale is error prone as it can easily lead to silent breakages with some locales! -->
        <module name = "MatchXpath">
            <property name="query" value="//METHOD_CALL[./DOT/IDENT[@text='toLowerCase' or @text='toUpperCase']]/ELIST[count(./*) = 0]"/>
            <message key="matchxpath.match" value="String#toLowerCase/toUpperCase calls must specify a locale, English recommended"/>
        </module>
    </module>
</module>