checkstyle.xml

<?xml version="1.0" ?>

<!DOCTYPE module PUBLIC
        "-//Checkstyle//DTD Checkstyle Configuration 1.2//EN"
        "https://checkstyle.org/dtds/configuration_1_2.dtd">

<module name="Checker">
    <module name="TreeWalker">

        <!-- No if/else/do/for/while without braces -->
        <module name="NeedBraces"/>

        <!-- No empty blocks -->
        <module name="EmptyBlock"/>

        <!-- Disallow unnecessary instantiation of Boolean, String -->
        <module name="IllegalInstantiation">
            <!-- property name="classes" value="java.lang.Boolean, java.lang.String"/ -->
            <property name="classes" value="java.lang.Boolean"/>
        </module>

        <!--  Import should be explicit, really needed and only from pure java packages -->
        <module name="AvoidStarImport" />
        <module name="UnusedImports" />
        <module name="IllegalImport" >
            <property name="regexp" value="true"/>
            <!-- Reject any org.junit import that's not also org.junit.jupiter: -->
            <property name="illegalClasses" value="^org\.junit\.(?!jupiter\.).+"/>
        </module>

        <!-- TODO: Find how to exclude spring application classes and uncomment -->
        <!-- Check https://checkstyle.org/config_filters.html#SuppressionXpathSingleFilter -->
        <!-- Utility class should not be instantiated, they must have a private constructor -->
        <!-- module name="HideUtilityClassConstructor" /-->

        <!-- No System.out.println() statements -->
        <module name="Regexp">
            <!-- no sysouts -->
            <property name="format" value="System\.out\.println"/>
            <property name="illegalPattern" value="true"/>
        </module>

        <!-- No trailing whitespace -->
        <module name="Regexp">
            <property name="format" value="[ \t]+$"/>
            <property name="illegalPattern" value="true"/>
            <property name="message" value="Trailing whitespace"/>
        </module>

        <!-- Use static import for mockito -->
        <module name="Regexp">
            <property name="format" value="^(?!import).*Mockito\."/>
            <property name="illegalPattern" value="true"/>
            <property name="message" value="Use static import for Mockito"/>
        </module>

        <module name="Regexp">
            <property name="format" value="^(?!import).*Assertions\."/>
            <property name="illegalPattern" value="true"/>
            <property name="message" value="Use static import for Assertions"/>
        </module>
    </module>
</module>