checkstyle.xml

<?xml version="1.0" encoding="UTF-8"?>
<!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="fileExtensions" value="java"/>
  <property name="severity" value="error"/>

  <module name="SuppressionFilter">
    <property name="file" value="checkstyle-suppressions.xml"/>
    <property name="optional" value="true"/>
  </module>

  <module name="FileTabCharacter"/>
  <module name="NewlineAtEndOfFile"/>

  <module name="LineLength">
    <property name="max" value="120"/>
    <property name="ignorePattern" value="^package.*|^import.*|a href|href|http://|https://|ftp://"/>
  </module>

  <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="TreeWalker">

    <module name="AvoidStarImport"/>
    <module name="IllegalImport"/>
    <module name="RedundantImport"/>
    <module name="UnusedImports">
      <property name="processJavadoc" value="false"/>
    </module>

    <module name="MethodLength"/>
    <module name="ParameterNumber"/>

    <module name="EmptyForIteratorPad"/>
    <module name="GenericWhitespace"/>
    <module name="MethodParamPad"/>
    <module name="NoWhitespaceAfter"/>
    <module name="NoWhitespaceBefore"/>
    <module name="OperatorWrap"/>
    <module name="ParenPad"/>
    <module name="TypecastParenPad"/>
    <module name="WhitespaceAfter"/>
    <module name="WhitespaceAround"/>

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

    <module name="AvoidNestedBlocks"/>
    <module name="EmptyBlock"/>

    <module name="EmptyStatement"/>
    <module name="EqualsHashCode"/>
    <module name="IllegalInstantiation"/>
    <module name="InnerAssignment"/>
    <module name="MissingSwitchDefault"/>
    <module name="MultipleVariableDeclarations"/>
    <module name="SimplifyBooleanExpression"/>
    <module name="SimplifyBooleanReturn"/>

    <module name="Indentation">
      <property name="basicOffset" value="4"/>
      <property name="braceAdjustment" value="0"/>
      <property name="caseIndent" value="4"/>
      <property name="throwsIndent" value="4"/>
    </module>
  </module>
</module>