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">
    <property name="charset" value="UTF-8"/>
    <property name="severity" value="error"/>
    <!-- File length -->
    <module name="FileLength">
        <property name="max" value="500"/>
    </module>

    <module name="FileTabCharacter"/>

    <!-- No trailing whitespace -->
    <module name="RegexpSingleline">
        <property name="format" value="\s+$"/>
        <property name="message" value="Line has trailing whitespace."/>
    </module>

    <!-- Newline at end of file -->
    <module name="NewlineAtEndOfFile">
        <property name="lineSeparator" value="lf"/>
    </module>

    <module name="TreeWalker">
        <!-- Naming conventions -->
        <module name="TypeName"/>
        <module name="MethodName"/>
        <module name="ConstantName"/>
        <module name="LocalVariableName"/>
        <module name="MemberName"/>
        <module name="ParameterName"/>
        <module name="PackageName"/>

        <!-- Imports -->
        <module name="UnusedImports"/>
        <module name="RedundantImport"/>
        <module name="AvoidStarImport"/>

        <!-- Whitespace -->
        <module name="WhitespaceAround">
            <property name="allowEmptyConstructors" value="true"/>
            <property name="allowEmptyMethods" value="true"/>
            <property name="allowEmptyTypes" value="true"/>
            <property name="allowEmptyLambdas" value="true"/>
        </module>
        <module name="GenericWhitespace"/>
        <module name="NoWhitespaceBefore"/>
        <module name="MethodParamPad"/>

        <!-- Blocks -->
        <module name="NeedBraces">
            <property name="allowSingleLineStatement" value="true"/>
        </module>
        <module name="RightCurly"/>

        <!-- Coding -->
        <module name="EqualsHashCode"/>
        <module name="SimplifyBooleanExpression"/>
        <module name="SimplifyBooleanReturn"/>
        <module name="StringLiteralEquality"/>
        <module name="MultipleVariableDeclarations"/>
        <module name="MissingSwitchDefault">
            <!-- Exhaustive switch expressions/statements don't need default -->
        </module>
        <module name="FallThrough"/>
        <module name="UpperEll"/>

        <!-- Modifiers -->
        <module name="ModifierOrder"/>
        <module name="RedundantModifier"/>

    </module>

    <!-- Line length (Checker-level in Checkstyle 10+) -->
    <module name="LineLength">
        <property name="max" value="120"/>
        <property name="fileExtensions" value="java"/>
        <property name="ignorePattern" value="^package.*|^import.*|a href|href|http://|https://|ftp://"/>
    </module>
</module>