Java CheckStyle. How To Format Your Java Code With CheckStyle

Oleksii Dushenin
14 min readJul 24, 2021

In a Spring Boot Application Overview Course, a simple spring boot application was created. In this course, we will review some tools that can be useful from the development perspective. Formatting the Java Code with CheckStyle is to be an initial post in the course.

The problem occurs in the fact that multiple developers contribute to the source code. Each of them has individual preferences for code formatting. As a result, the code is inconsistent. Moreover, it brings additional problems. The first developer can write the code in the first style. Then the second developer will apply automatic formatting to this code based on his own style and it will be changed. During code review, you will constantly see that a huge set of changes is introduced in a pull request. However, it was just reformatting without any useful business logic.

To overcome this problem CheckStyle can be used.

Project Creation

Let’s create the initial Gradle project. E.g. if you use Intellij IDEA you just create a new Gradle project and provide some meta-information.

The goal of this post is to validate the Java source code with CheckStyle. So, let’s create some classes with problematic formatting.

package com.datamify.development.codestyle;public class Tuple
{

public void doSomething( int
param) {
System.out.println("Param: " + param);
}

}

It will be our test class to validate.

Java CheckStyle Configuration

To validate our Java source code we have to apply Gradle Checkstyle Plugin.

To begin with, we add the checkstyle plugin into the build.gradle file.

plugins {
id 'checkstyle'
}

This is a minimum possible configuration in build.gradle. However, we add additional options. The first option is a checkstyle plugin configuration.

checkstyle {
toolVersion '8.40'
maxWarnings = 0
ignoreFailures false
}

As you can see we have next options:

  • toolVersion. Checkstyle version is explicitly specified. It is done because the plugin requires configuration file with the rules to apply (it will be added later). Configuration file can have sections from the one version, which cannot be parsed by the plugin with another version.
  • maxVarnings. The default behavior is to create a file with warnings. However, the build will be successful. We want to fail the build, as a result maxWarnings is 0.
  • ignoreFailures. In case of errors the build is about to fail with the false option.

Let’s also set the report types.

tasks.withType(Checkstyle) {
reports {
xml.required = true
html.required = true
}
}

As you can see, an XML and HTML reports are expected.

More options can be found in Gradle Plugin Documentation.

The full build.gradle file has the next form:

plugins {
id 'java'
id 'checkstyle'
}
group 'com.datamify'
version '1.0-SNAPSHOT'
repositories {
mavenCentral()
}
dependencies {
testImplementation 'org.junit.jupiter:junit-jupiter-api:5.7.0'
testRuntimeOnly 'org.junit.jupiter:junit-jupiter-engine:5.7.0'
}
test {
useJUnitPlatform()
}
checkstyle {
toolVersion '8.40'
maxWarnings = 0
ignoreFailures false
}
tasks.withType(Checkstyle) {
reports {
xml.required = true
html.required = true
}
}

Java CheckStyle Configuration File

As was stated previously, the configuration file is required. In this article, Google Checks will be used. However, you can have another preference in your project. You can change some sections or create a configuration from scratch ( Configuration details).

The only problem is the versioning. We will get this file not from the branch but from the 8.40 tag (the version of the plugin).

We save the content of this file in a predefined location

PROJECT_ROOT/config/checkstyle.xml

In our case, it has the next form:

<?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">
<!--
If you set the basedir property below, then all reported file
names will be relative to the specified directory. See
https://checkstyle.org/config.html#Checker

<property name="basedir" value="${basedir}"/>
-->

<metadata name="org.checkstyle.principle" value="Practice What You Preach"/>
<metadata name="org.checkstyle.principle.description"
value="In our config we should use all Checks that Checkstyle has"/>

<property name="cacheFile" value="${checkstyle.cache.file}"/>

<property name="severity" value="error"/>

<property name="fileExtensions" value="java, properties, xml, vm, g, g4, dtd"/>

<!-- BeforeExecutionFileFilters is required for sources that are based on java9 -->
<module name="BeforeExecutionExclusionFileFilter">
<property name="fileNamePattern" value="module\-info\.java$" />
</module>

<!-- Filters -->
<module name="SeverityMatchFilter">
<!-- report all violations except ignore -->
<property name="severity" value="ignore"/>
<property name="acceptOnMatch" value="false"/>
</module>
<module name="SuppressionFilter">
<property name="file" value="${checkstyle.suppressions.file}"/>
</module>
<!-- Tone down the checking for test code -->
<module name="SuppressionSingleFilter">
<property name="checks" value="JavadocPackage"/>
<property name="files" value=".*[\\/]src[\\/](test|it)[\\/]"/>
</module>
<module name="SuppressionSingleFilter">
<property name="checks" value="JavadocMethod"/>
<property name="files" value=".*[\\/]src[\\/](test|it)[\\/].*(?&lt;!Support)\.java"/>
</module>
<module name="SuppressWarningsFilter"/>
<module name="SuppressWithPlainTextCommentFilter">
<!--
Use suppressions.xml for suppressions, this is only example.
checkFormat will prevent suppression comments from being valid.
-->
<property name="checkFormat" value="IGNORETHIS"/>
<property name="offCommentFormat" value="CSOFF\: .*"/>
<property name="onCommentFormat" value="CSON\: .*"/>
</module>

<!-- Headers -->
<module name="Header">
<property name="headerFile" value="${checkstyle.header.file}"/>
<property name="fileExtensions" value="java"/>
<property name="id" value="header"/>
</module>
<module name="RegexpHeader">
<property name="headerFile" value="${checkstyle.regexp.header.file}"/>
<property name="fileExtensions" value="java"/>
</module>

<!-- Javadoc Comments -->
<module name="JavadocPackage">
<property name="allowLegacy" value="false"/>
</module>

<!-- Miscellaneous -->
<module name="NewlineAtEndOfFile"/>
<module name="Translation">
<property name="requiredTranslations" value="de, fr, fi, es, pt, ja, tr, zh"/>
</module>
<module name="UniqueProperties"/>
<module name="OrderedProperties" />

<!-- Regexp -->
<module name="RegexpMultiline">
<property name="id" value="regexpMultilineDefault"/>
</module>
<module name="RegexpMultiline">
<property name="id" value="noIndentationConfigExamples"/>
<property name="format" value="&lt;source&gt;\r?\n\s+"/>
<property name="fileExtensions" value="xml"/>
<property name="message" value="Content of source tag should not be Indented"/>
</module>
<module name="RegexpMultiline">
<property name="id" value="noConsecutiveLines"/>
<property name="format" value="\r?\n[\t ]*\r?\n[\t ]*\r?\n"/>
<property name="fileExtensions" value="java,xml,properties"/>
<property name="message" value="Unnecessary consecutive lines"/>
</module>
<module name="RegexpMultiline">
<property name="id" value="commentFirstSentenceMultiline"/>
<property name="format" value="/\*\*\W+\* +\p{javaLowerCase}"/>
<property name="fileExtensions" value="java"/>
<property name="message"
value="First sentence in a comment should start with a capital letter"/>
</module>
<module name="RegexpMultiline">
<property name="id" value="noEmptyFile"/>
<property name="format" value="^\s*$" />
<property name="matchAcrossLines" value="true" />
<property name="message" value="Empty file is not allowed" />
</module>
<module name="RegexpSingleline">
<property name="id" value="noTrailingWhitespace"/>
<property name="format" value="\s+$"/>
<property name="minimum" value="0"/>
<property name="maximum" value="0"/>
<property name="message" value="Trailing whitespace is not allowed"/>
</module>
<!-- This is needed for correct metadata generation -->
<module name="RegexpSingleline">
<property name="id" value="propertyTypeOnNewLine"/>
<property name="format" value="^ \* .+(Type|Default value|Validation type) is \{@code "/>
<property name="minimum" value="0"/>
<property name="maximum" value="0"/>
<property name="message" value="Property attribute should be on new javadoc line"/>
</module>
<module name="RegexpSingleline">
<property name="id" value="commentFirstSentenceSingleline"/>
<property name="format" value="/\*\* +\p{javaLowerCase}"/>
<property name="fileExtensions" value="java"/>
<property name="message"
value="First sentence in a comment should start with a capital letter"/>
</module>
<module name="RegexpSingleline">
<property name="id" value="lineLengthGrammar"/>
<property name="format" value="^(?!(.*http|import)).{101,}$"/>
<property name="fileExtensions" value="g, g4"/>
<property name="message" value="Line should not be longer than 100 symbols"/>
</module>
<module name="RegexpSingleline">
<property name="id" value="lineLengthXml"/>
<property name="format"
value="^(?!(\s*,?\s*&lt;a href=&quot;[^&quot;]+&quot;&gt;|.*http)).{101,}$"/>
<property name="fileExtensions" value="xml, vm"/>
<property name="message" value="Line should not be longer than 100 symbols"/>
</module>
<!--
Links to .dtd files should start with "/", "http://" or "https://",
otherwise they will be broken after archiving the documentation.
See https://github.com/checkstyle/checkstyle/issues/7340 for details.
-->
<module name="RegexpSingleline">
<property name="id" value="noRelativeLinks"/>
<property name="format" value="href=&quot;(?!\/|https?:\/\/).*?\.dtd&quot;"/>
<property name="fileExtensions" value="xml, vm"/>
<property name="message"
value="Relative links to DTD files are prohibited. Please use absolute path or uri instead."/>
</module>
<module name="RegexpSingleline">
<property name="id" value="noSourceforgeNetLinks"/>
<property name="format" value="checkstyle\.sourceforge\.net"/>
<property name="message"
value="Old site links should not be used, please use https://checkstyle.org"/>
</module>
<module name="RegexpSingleline">
<property name="id" value="noSourceforgeIoLinks"/>
<property name="format" value="checkstyle\.sourceforge\.io"/>
<property name="message"
value="Old site links should not be used, please use https://checkstyle.org"/>
</module>
<module name="RegexpSingleline">
<property name="id" value="noPackageCommentWithOtherVisibility"/>
<property name="format" value="/\*\s+package\s+\*/\s+(private|protected|public)"/>
<property name="fileExtensions" value="java"/>
<property name="message"
value="Package comment marker should not be used if other visibility is defined"/>
</module>
<module name="RegexpOnFilename">
<property name="id" value="regexpOnFilenameWithSpace"/>
</module>
<module name="RegexpOnFilename">
<property name="id" value="javaFileLocation"/>
<property name="folderPattern" value="[\\/]src[\\/]\w+[\\/]java[\\/]"/>
<property name="fileNamePattern" value="\.java$"/>
<property name="match" value="false"/>
<message key="regexp.filepath.mismatch"
value="Only java files should be located in the ''src/*/java'' folders."/>
</module>
<module name="RegexpOnFilename">
<property name="id" value="xmlFileLocation"/>
<property name="folderPattern" value="[\\/]src[\\/]xdocs[\\/]"/>
<property name="fileNamePattern" value="\.(xml)|(vm)$"/>
<property name="match" value="false"/>
<message key="regexp.filepath.mismatch"
value="All files in the ''src/xdocs'' folder should have the ''xml'' or ''vm'' extension."/>
</module>
<module name="RegexpOnFilename">
<property name="id" value="testFileLocation"/>
<property name="folderPattern" value="[\\/]src[\\/]it[\\/]java[\\/]"/>
<property name="fileNamePattern" value="^((\w+Test)|(\w+TestSupport)|(Abstract\w+))\.java$"/>
<property name="match" value="false"/>
<message key="regexp.filepath.mismatch"
value="All files in the ''src/it/java'' folder
should be named ''*Test.java'' or ''Abstract*.java''."/>
</module>

<!-- Size Violations -->
<module name="FileLength">
<property name="fileExtensions" value="java"/>
</module>
<module name="LineLength">
<property name="fileExtensions" value="java"/>
<property name="max" value="100"/>
<property name="ignorePattern" value="^ *\* *([^ ]+|\{@code .*|&lt;a href=&quot;[^&quot;]+&quot;&gt;)$"/>
</module>

<!-- Whitespace -->
<module name="FileTabCharacter">
<property name="eachLine" value="false"/>
</module>

<module name="TreeWalker">
<property name="tabWidth" value="4"/>

<!-- Annotations -->
<module name="AnnotationLocation">
<property name="tokens" value="ANNOTATION_DEF"/>
<property name="tokens" value="ANNOTATION_FIELD_DEF"/>
<property name="tokens" value="PACKAGE_DEF"/>
<property name="tokens" value="ENUM_CONSTANT_DEF"/>
<property name="tokens" value="VARIABLE_DEF"/>
<property name="allowSamelineSingleParameterlessAnnotation" value="false"/>
</module>
<module name="AnnotationOnSameLine">
<!-- we can not use it as it conflicts with AnnotationLocation -->
<property name="severity" value="ignore"/>
<property name="tokens" value="METHOD_DEF"/>
<property name="tokens" value="CTOR_DEF"/>
<property name="tokens" value="TYPECAST"/>
<property name="tokens" value="DOT"/>
<property name="tokens" value="CLASS_DEF"/>
<property name="tokens" value="ENUM_DEF"/>
<property name="tokens" value="INTERFACE_DEF"/>
<property name="tokens" value="TYPE_ARGUMENT"/>
<property name="tokens" value="ANNOTATION_DEF"/>
<property name="tokens" value="LITERAL_NEW"/>
<property name="tokens" value="LITERAL_THROWS"/>
<property name="tokens" value="VARIABLE_DEF"/>
<property name="tokens" value="PARAMETER_DEF"/>
<property name="tokens" value="IMPLEMENTS_CLAUSE"/>
<property name="tokens" value="ANNOTATION_FIELD_DEF"/>
<property name="tokens" value="RECORD_DEF"/>
<property name="tokens" value="COMPACT_CTOR_DEF"/>
</module>
<module name="AnnotationUseStyle"/>
<module name="MissingDeprecated"/>
<module name="MissingOverride"/>
<module name="PackageAnnotation"/>
<module name="SuppressWarnings">
<property name="format" value="^((?!unchecked|deprecation|rawtypes|resource).)*$"/>
<message key="suppressed.warning.not.allowed"
value="The warning ''{0}'' cannot be suppressed at this location.
Only few javac warnings are allowed to suppress.
If try to suppress checkstyle/pmd/..... violation please do this in their config file.
If you try to suppress IntelliJ IDEA inspection,
please use javadoc block tag @noinspection"
/>
</module>
<module name="SuppressWarningsHolder"/>

<!-- Block Checks -->
<module name="AvoidNestedBlocks">
<property name="allowInSwitchCase" value="true"/>
</module>
<module name="EmptyBlock">
<property name="tokens" value="LITERAL_CATCH"/>
<property name="tokens" value="ARRAY_INIT"/>
<property name="tokens" value="LITERAL_DEFAULT"/>
<property name="tokens" value="LITERAL_CASE"/>
<property name="tokens" value="INSTANCE_INIT"/>
<property name="tokens" value="LITERAL_DO"/>
<property name="tokens" value="LITERAL_ELSE"/>
<property name="tokens" value="LITERAL_FINALLY"/>
<property name="tokens" value="LITERAL_FOR"/>
<property name="tokens" value="LITERAL_IF"/>
<property name="tokens" value="LITERAL_SWITCH"/>
<property name="tokens" value="LITERAL_SYNCHRONIZED"/>
<property name="tokens" value="LITERAL_TRY"/>
<property name="tokens" value="LITERAL_WHILE"/>
<property name="tokens" value="STATIC_INIT"/>
<property name="option" value="text"/>
</module>
<module name="EmptyCatchBlock"/>
<module name="LeftCurly"/>
<module name="NeedBraces"/>
<module name="NeedBraces">
<property name="tokens" value="LAMBDA"/>
<property name="allowSingleLineStatement" value="true"/>
</module>
<module name="RightCurly">
<property name="tokens" value="METHOD_DEF"/>
<property name="tokens" value="CTOR_DEF"/>
<property name="tokens" value="CLASS_DEF"/>
<property name="tokens" value="INSTANCE_INIT"/>
<property name="tokens" value="LITERAL_FOR"/>
<property name="tokens" value="STATIC_INIT"/>
<property name="tokens" value="LITERAL_WHILE"/>
<property name="tokens" value="LITERAL_CATCH"/>
<property name="tokens" value="LITERAL_ELSE"/>
<property name="tokens" value="LITERAL_FINALLY"/>
<property name="tokens" value="LITERAL_IF"/>
<property name="tokens" value="LITERAL_TRY"/>
<property name="tokens" value="ANNOTATION_DEF"/>
<property name="tokens" value="ENUM_DEF"/>
<property name="tokens" value="RECORD_DEF"/>
<property name="tokens" value="COMPACT_CTOR_DEF"/>
<property name="option" value="alone"/>
</module>
<module name="RightCurly">
<property name="tokens" value="LITERAL_DO"/>
<property name="option" value="same"/>
</module>
<module name="RightCurly">
<property name="tokens" value="INTERFACE_DEF"/>
<property name="option" value="alone_or_singleline"/>
</module>

<!-- Class Design -->
<module name="DesignForExtension">
<property name="ignoredAnnotations"
value="Override, Test, Before, After, BeforeClass, AfterClass"/>
<property name="ignoredAnnotations"
value="BeforeAll, AfterAll, BeforeEach, AfterEach"/>
</module>
<module name="FinalClass"/>
<module name="HideUtilityClassConstructor"/>
<module name="InnerTypeLast"/>
<module name="InterfaceIsType"/>
<module name="MutableException"/>
<module name="OneTopLevelClass"/>
<module name="ThrowsCount">
<property name="max" value="2"/>
</module>
<module name="VisibilityModifier">
<property name="ignoreAnnotationCanonicalNames"
value="org.junit.Rule, org.junit.jupiter.api.io.TempDir"/>
</module>

<!-- Coding -->
<module name="ArrayTrailingComma"/>
<module name="AvoidDoubleBraceInitialization"/>
<module name="AvoidInlineConditionals"/>
<module name="AvoidNoArgumentSuperConstructorCall"/>
<module name="CovariantEquals"/>
<module name="DeclarationOrder"/>
<module name="DefaultComesLast"/>
<module name="EmptyStatement"/>
<module name="EqualsAvoidNull"/>
<module name="EqualsHashCode"/>
<module name="ExplicitInitialization"/>
<module name="FallThrough"/>
<module name="FinalLocalVariable"/>
<module name="HiddenField">
<property name="ignoreConstructorParameter" value="true"/>
<property name="ignoreSetter" value="true"/>
<property name="setterCanReturnItsClass" value="true"/>
</module>
<module name="IllegalCatch">
<property name="illegalClassNames"
value="java.lang.Exception,
java.lang.Throwable,
java.lang.RuntimeException,
java.lang.NullPointerException"/>
</module>
<module name="IllegalInstantiation">
<property name="classes"
value="org.xml.sax.SAXException, org.xml.sax.SAXParseException,
org.apache.commons.beanutils.ConversionException,
org.antlr.v4.runtime.misc.ParseCancellationException,
antlr.RecognitionException, antlr.TokenStreamException,
antlr.TokenStreamRecognitionException, antlr.ANTLRException,
java.lang.StringBuffer"/>
</module>
<module name="IllegalThrows"/>
<module name="IllegalToken">
<property name="tokens" value="LABELED_STAT"/>
<property name="tokens" value="LITERAL_NATIVE"/>
<property name="tokens" value="LITERAL_VOLATILE"/>
<property name="tokens" value="LITERAL_ASSERT"/>
</module>
<module name="IllegalTokenText">
<property name="tokens" value="STRING_LITERAL"/>
<property name="format" value="^(US-ASCII|ISO-8859-1|UTF-8|UTF-16BE|UTF-16LE|UTF-16)$"/>
<property name="ignoreCase" value="true"/>
</module>
<module name="IllegalType">
<property name="illegalClassNames"
value="java.util.HashSet, HashSet, java.util.LinkedHashMap, LinkedHashMap,
java.util.TreeMap, TreeMap, java.util.HashMap, HashMap,
java.util.LinkedHashSet, LinkedHashSet, java.util.TreeSet, TreeSet,
java.lang.StringBuffer, StringBuffer"/>
</module>
<module name="InnerAssignment"/>
<module name="MagicNumber"/>
<module name="MatchXpath">
<property name="query" value="//CLASS_DEF[@text!='Checker' and @text!='Main']
//LITERAL_CATCH//METHOD_CALL[.//IDENT[@text = 'printStackTrace']]/.."/>
<message key="matchxpath.match" value="Avoid using 'printStackTrace'."/>
</module>
<module name="MatchXpath">
<property name="query" value="//METHOD_DEF/MODIFIERS//
ANNOTATION[./IDENT[@text='Test']]/ANNOTATION_MEMBER_VALUE_PAIR
[./IDENT[@text='expected']]"/>
<message key="matchxpath.match" value="Avoid using 'expected' attribute in Test annotation."/>
</module>
<module name="MissingCtor">
<!--
we will not use that fanatic validation, extra code is not good
But this Check will exists as it was created by community demand.
-->
<property name="severity" value="ignore"/>
</module>
<module name="MissingSwitchDefault"/>
<module name="ModifiedControlVariable"/>
<module name="MultipleStringLiterals"/>
<module name="MultipleVariableDeclarations"/>
<module name="NestedForDepth">
<property name="max" value="2"/>
</module>
<module name="NestedIfDepth">
<property name="max" value="3"/>
</module>
<module name="NestedTryDepth"/>
<module name="NoArrayTrailingComma">
<!-- This Check is conflicting with ArrayTrailingComma -->
<property name="severity" value="ignore"/>
</module>
<module name="NoClone"/>
<module name="NoCodeInFile"/>
<module name="NoEnumTrailingComma">
<!-- This Check is conflicting with our vision of code
to be same as ArrayTrailingComma requires it -->
<property name="severity" value="ignore"/>
</module>
<module name="NoFinalizer"/>
<module name="OneStatementPerLine"/>
<module name="OverloadMethodsDeclarationOrder"/>
<module name="PackageDeclaration"/>
<module name="ParameterAssignment"/>
<module name="RequireThis"/>
<module name="ReturnCount">
<property name="max" value="1"/>
<property name="maxForVoid" value="0"/>
</module>
<module name="SimplifyBooleanExpression"/>
<module name="SimplifyBooleanReturn"/>
<module name="StringLiteralEquality"/>
<module name="SuperClone"/>
<module name="SuperFinalize"/>
<module name="UnnecessaryParentheses"/>
<module name="UnnecessarySemicolonAfterOuterTypeDeclaration"/>
<module name="UnnecessarySemicolonAfterTypeMemberDeclaration"/>
<module name="UnnecessarySemicolonInEnumeration"/>
<module name="UnnecessarySemicolonInTryWithResources"/>
<module name="VariableDeclarationUsageDistance"/>

<!-- Filters -->
<module name="SuppressionCommentFilter">
<!--
Use suppressions.xml for suppressions, this is only example.
checkFormat will prevent suppression comments from being valid.
-->
<property name="checkFormat" value="IGNORETHIS"/>
<property name="offCommentFormat" value="CSOFF\: .*"/>
<property name="onCommentFormat" value="CSON\: .*"/>
</module>
<module name="SuppressionXpathFilter">
<property name="file" value="${checkstyle.suppressions-xpath.file}"/>
</module>
<!-- Tone down the checking for test code -->
<module name="SuppressionXpathSingleFilter">
<property name="files" value="[\\/]internal[\\/].*[\\/]\w+Util\.java"/>
<property name="checks" value="IllegalCatch"/>
</module>
<module name="SuppressionXpathSingleFilter">
<property name="files" value=".*[\\/]src[\\/]test[\\/]"/>
<property name="checks" value="EmptyBlock"/>
</module>
<module name="SuppressionXpathSingleFilter">
<property name="files" value=".*[\\/]src[\\/](test|it)[\\/]"/>
<property name="checks" value="JavadocVariable"/>
</module>
<module name="SuppressionXpathSingleFilter">
<property name="files" value=".*[\\/]src[\\/](test|it)[\\/]"/>
<property name="checks" value="JavadocType"/>
</module>
<module name="SuppressionXpathSingleFilter">
<property name="files" value=".*[\\/]src[\\/](test|it)[\\/]"/>
<property name="checks" value="MagicNumber"/>
</module>
<module name="SuppressionXpathSingleFilter">
<property name="files" value=".*[\\/]src[\\/](test|it)[\\/]"/>
<property name="checks" value="AvoidStaticImport"/>
</module>
<module name="SuppressionXpathSingleFilter">
<property name="files" value=".*[\\/]src[\\/](test|it)[\\/]"/>
<property name="checks" value="WriteTag"/>
</module>
<module name="SuppressionXpathSingleFilter">
<property name="files" value=".*[\\/]src[\\/](test|it)[\\/]"/>
<property name="checks" value="MethodCount"/>
</module>
<!-- Fixing these cases will decrease code readability -->
<module name="SuppressionXpathSingleFilter">
<property name="files" value=".*[\\/]src[\\/](test|it)[\\/]"/>
<property name="checks" value="MultipleStringLiterals"/>
</module>
<module name="SuppressWithNearbyCommentFilter">
<property name="commentFormat"
value="-@cs\[(\w{8,}(\|\w{8,})*)\] \w[\(\)\-\.\'\`\,\:\;\w ]{10,}"/>
<property name="checkFormat" value="$1"/>
<property name="influenceFormat" value="3"/>
</module>

<!-- Imports -->
<module name="AvoidStarImport"/>
<module name="AvoidStaticImport"/>
<module name="CustomImportOrder">
<property name="customImportOrderRules"
value="STATIC###STANDARD_JAVA_PACKAGE###SPECIAL_IMPORTS###THIRD_PARTY_PACKAGE"/>
<property name="standardPackageRegExp" value="^java\."/>
<property name="specialImportsRegExp" value="^javax\."/>
<property name="thirdPartyPackageRegExp" value="^org\."/>
<property name="sortImportsInGroupAlphabetically" value="true"/>
<property name="separateLineBetweenGroups" value="true"/>
</module>
<module name="IllegalImport"/>
<module name="ImportControl">
<property name="id" value="ImportControlMain"/>
<property name="file" value="${checkstyle.importcontrol.file}"/>
<property name="path" value="^.*[\\/]src[\\/]main[\\/].*$"/>
</module>
<module name="ImportControl">
<property name="id" value="ImportControlTest"/>
<property name="file" value="${checkstyle.importcontroltest.file}"/>
<property name="path" value="^.*[\\/]src[\\/]test[\\/].*$"/>
</module>
<module name="ImportOrder">
<property name="groups" value="/^java\./,javax,org"/>
<property name="ordered" value="true"/>
<property name="separated" value="true"/>
<property name="option" value="top"/>
<property name="sortStaticImportsAlphabetically" value="true"/>
</module>
<module name="RedundantImport"/>
<module name="UnusedImports"/>

<!-- Javadoc Comments -->
<module name="AtclauseOrder"/>
<module name="InvalidJavadocPosition"/>
<module name="JavadocBlockTagLocation">
<!-- default tags -->
<property name="tags" value="author, deprecated, exception, hidden, param, provides"/>
<property name="tags" value="return, see, serial, serialData, serialField, since, throws"/>
<property name="tags" value="uses, version"/>
<!-- additional tags used in the project -->
<property name="tags" value="noinspection"/>
</module>
<module name="JavadocContentLocation"/>
<module name="JavadocMethod">
<property name="validateThrows" value="true"/>
</module>
<module name="JavadocMissingLeadingAsterisk"/>
<module name="JavadocMissingWhitespaceAfterAsterisk"/>
<module name="JavadocParagraph"/>
<module name="JavadocStyle">
<property name="scope" value="public"/>
</module>
<module name="JavadocTagContinuationIndentation"/>
<module name="JavadocType">
<!-- avoid errors on tag '@noinspection' -->
<property name="allowUnknownTags" value="true"/>
</module>
<module name="JavadocVariable"/>
<module name="MissingJavadocMethod">
<property name="allowMissingPropertyJavadoc" value="true"/>
<property name="scope" value="private"/>
</module>
<module name="MissingJavadocPackage"/>
<module name="MissingJavadocType">
<property name="scope" value="private"/>
</module>
<module name="NonEmptyAtclauseDescription"/>
<module name="SingleLineJavadoc"/>
<module name="WriteTag"/>
<module name="SummaryJavadoc"/>
<module name="RequireEmptyLineBeforeBlockTagGroup"/>

<!-- Metrics -->
<module name="BooleanExpressionComplexity">
<property name="max" value="7"/>
</module>
<module name="ClassDataAbstractionCoupling">
<!-- Default classes are also listed -->
<property name="excludedClasses"
value="boolean, byte, char, double, float, int, long, short, void,
Boolean, Byte, Character, Double, Float, Integer, Long, Short, Void,
Object, Class, String, StringBuffer, StringBuilder,
ArrayIndexOutOfBoundsException, Exception, RuntimeException,
IllegalArgumentException, IllegalStateException,
IndexOutOfBoundsException, NullPointerException, Throwable,
SecurityException, UnsupportedOperationException, List, ArrayList,
Deque, Queue, LinkedList, Set, HashSet, SortedSet, TreeSet, Map,
HashMap, SortedMap, TreeMap, DetailsAST, CheckstyleException,
UnsupportedEncodingException, BuildException, ConversionException,
FileNotFoundException, TestException"/>
</module>
<module name="ClassFanOutComplexity">
<property name="max" value="25"/>
<!-- Default classes are also listed -->
<property name="excludedClasses"
value="boolean, byte, char, double, float, int, long, short,
void, Boolean, Byte, Character, Double, Float, Integer,
Long, Short, Void, Object, Class, String, StringBuffer,
StringBuilder, ArrayIndexOutOfBoundsException, Exception,
RuntimeException, IllegalArgumentException, IllegalStateException,
IndexOutOfBoundsException, NullPointerException, Throwable,
SecurityException, UnsupportedOperationException, List, ArrayList,
Deque, Queue, LinkedList, Set, HashSet, SortedSet, TreeSet, Map,
HashMap, SortedMap, TreeMap, DetailsAST, CheckstyleException,
UnsupportedEncodingException, BuildException, ConversionException,
FileNotFoundException, TestException, Log, Sets, Multimap,
TokenStreamRecognitionException, RecognitionException,
TokenStreamException, IOException, Override, Deprecated, SafeVarargs,
SuppressWarnings, FunctionalInterface"/>
</module>
<module name="CyclomaticComplexity">
<property name="switchBlockAsSingleDecisionPoint" value="true"/>
</module>
<module name="JavaNCSS"/>
<module name="NPathComplexity"/>

<!-- Misc -->
<module name="ArrayTypeStyle"/>
<module name="AvoidEscapedUnicodeCharacters">
<property name="allowIfAllCharactersEscaped" value="true"/>
</module>
<module name="CommentsIndentation"/>
<module name="DescendantToken"/>
<module name="FinalParameters">
<!--
we will not use that fanatic validation, extra modifiers pollute a code
it is better to use extra validation(Check) that argument is reassigned
But this Check will exists as it was created by community demand.
-->
<property name="severity" value="ignore"/>
</module>
<module name="Indentation">
<property name="basicOffset" value="4"/>
<property name="braceAdjustment" value="0"/>
<property name="caseIndent" value="4"/>
<property name="throwsIndent" value="8"/>
</module>
<module name="OuterTypeFilename"/>
<module name="TodoComment">
<property name="format" value="(TODO)|(FIXME)" />
</module>
<!-- till https://github.com/checkstyle/checkstyle/issues/7388 -->
<module name="TodoComment">
<property name="id" value="commentStartWithSpace"/>
<property name="format" value="^([^\s\/*])"/>
<message key="todo.match" value="Comment text should start with space."/>
</module>
<module name="TrailingComment"/>
<module name="UncommentedMain">
<property name="excludedClasses" value="\.(Main|JavadocPropertiesGenerator)$"/>
</module>
<module name="UpperEll"/>

<!-- Modifiers -->
<module name="ClassMemberImpliedModifier">
<!-- effectively the opposite of RedundantModifier, so output must be ignored -->
<property name="severity" value="ignore"/>
</module>
<module name="InterfaceMemberImpliedModifier">
<!-- effectively the opposite of RedundantModifier, so output must be ignored -->
<property name="severity" value="ignore"/>
</module>
<module name="ModifierOrder"/>
<module name="RedundantModifier"/>

<!-- Naming Conventions -->
<module name="AbbreviationAsWordInName">
<property name="ignoreFinal" value="false"/>
<property name="allowedAbbreviationLength" value="0"/>
<property name="allowedAbbreviations" value="AST"/>
</module>
<module name="AbstractClassName"/>
<module name="ClassTypeParameterName"/>
<module name="RecordTypeParameterName"/>
<module name="RecordComponentName"/>
<module name="ConstantName"/>
<module name="InterfaceTypeParameterName"/>
<module name="LocalFinalVariableName"/>
<module name="LocalVariableName">
<property name="format" value="^(id)|([a-z][a-z0-9][a-zA-Z0-9]+)$"/>
<property name="allowOneCharVarInForLoop" value="true"/>
</module>
<module name="MemberName">
<property name="format" value="^(id)|([a-z][a-z0-9][a-zA-Z0-9]+)$"/>
</module>
<module name="MethodName"/>
<module name="MethodTypeParameterName"/>
<module name="PackageName"/>
<module name="ParameterName">
<property name="format" value="^(id)|([a-z][a-z0-9][a-zA-Z0-9]+)$"/>
<property name="ignoreOverridden" value="true"/>
</module>
<module name="LambdaParameterName">
<property name="format" value="^(id)|([a-z][a-z0-9][a-zA-Z0-9]+)$"/>
</module>
<module name="CatchParameterName">
<property name="format" value="^(ex|[a-z][a-z][a-zA-Z]+)$"/>
</module>
<module name="StaticVariableName">
<property name="format" value="^(id)|([a-z][a-z0-9][a-zA-Z0-9]+)$"/>
</module>
<module name="TypeName"/>
<module name="PatternVariableName"/>
<module name="IllegalIdentifierName"/>

<!-- Regexp -->
<module name="Regexp"/>
<module name="RegexpSinglelineJava"/>
<module name="RegexpSinglelineJava">
<property name="format" value="[^\p{ASCII}]"/>
<property name="ignoreComments" value="true"/>
</module>

<!-- Size Violations -->
<module name="AnonInnerLength"/>
<module name="ExecutableStatementCount">
<property name="max" value="30"/>
</module>
<module name="LambdaBodyLength"/>
<module name="MethodCount">
<property name="maxTotal" value="34"/>
</module>
<module name="MethodLength"/>
<module name="OuterTypeNumber"/>
<module name="ParameterNumber"/>
<module name="RecordComponentNumber"/>

<!-- Whitespace -->
<module name="EmptyForInitializerPad"/>
<module name="EmptyForIteratorPad"/>
<module name="EmptyLineSeparator">
<property name="allowNoEmptyLineBetweenFields" value="true"/>
<property name="allowMultipleEmptyLinesInsideClassMembers" value="false"/>
</module>
<module name="GenericWhitespace"/>
<module name="MethodParamPad"/>
<module name="NoLineWrap"/>
<module name="NoWhitespaceAfter">
<property name="tokens" value="ARRAY_INIT"/>
<property name="tokens" value="AT"/>
<property name="tokens" value="BNOT"/>
<property name="tokens" value="DEC"/>
<property name="tokens" value="DOT"/>
<property name="tokens" value="INC"/>
<property name="tokens" value="LNOT"/>
<property name="tokens" value="UNARY_MINUS"/>
<property name="tokens" value="UNARY_PLUS"/>
<property name="tokens" value="ARRAY_DECLARATOR"/>
<property name="tokens" value="INDEX_OP"/>
<property name="tokens" value="METHOD_REF"/>
</module>
<module name="NoWhitespaceBefore"/>
<module name="NoWhitespaceBefore">
<property name="tokens" value="DOT"/>
<property name="tokens" value="METHOD_REF"/>
<property name="allowLineBreaks" value="true"/>
</module>
<module name="OperatorWrap">
<property name="tokens" value="QUESTION"/>
<property name="tokens" value="COLON"/>
<property name="tokens" value="EQUAL"/>
<property name="tokens" value="NOT_EQUAL"/>
<property name="tokens" value="DIV"/>
<property name="tokens" value="PLUS"/>
<property name="tokens" value="MINUS"/>
<property name="tokens" value="STAR"/>
<property name="tokens" value="MOD"/>
<property name="tokens" value="SR"/>
<property name="tokens" value="BSR"/>
<property name="tokens" value="GE"/>
<property name="tokens" value="GT"/>
<property name="tokens" value="SL"/>
<property name="tokens" value="LE"/>
<property name="tokens" value="LT"/>
<property name="tokens" value="BXOR"/>
<property name="tokens" value="BOR"/>
<property name="tokens" value="LOR"/>
<property name="tokens" value="BAND"/>
<property name="tokens" value="LAND"/>
<property name="tokens" value="TYPE_EXTENSION_AND"/>
<property name="tokens" value="LITERAL_INSTANCEOF"/>
<property name="tokens" value="METHOD_REF"/>
<property name="option" value="nl"/>
</module>
<module name="OperatorWrap">
<property name="tokens" value="ASSIGN"/>
<property name="tokens" value="DIV_ASSIGN"/>
<property name="tokens" value="PLUS_ASSIGN"/>
<property name="tokens" value="MINUS_ASSIGN"/>
<property name="tokens" value="STAR_ASSIGN"/>
<property name="tokens" value="MOD_ASSIGN"/>
<property name="tokens" value="SR_ASSIGN"/>
<property name="tokens" value="BSR_ASSIGN"/>
<property name="tokens" value="SL_ASSIGN"/>
<property name="tokens" value="BXOR_ASSIGN"/>
<property name="tokens" value="BOR_ASSIGN"/>
<property name="tokens" value="BAND_ASSIGN"/>
<property name="option" value="eol"/>
</module>
<module name="ParenPad"/>
<module name="SeparatorWrap">
<property name="tokens" value="DOT"/>
<property name="tokens" value="AT"/>
<property name="tokens" value="METHOD_REF"/>
<property name="option" value="nl"/>
</module>
<module name="SeparatorWrap">
<property name="tokens" value="COMMA"/>
<property name="tokens" value="RBRACK"/>
<property name="tokens" value="ARRAY_DECLARATOR"/>
<property name="tokens" value="ELLIPSIS"/>
<property name="tokens" value="SEMI"/>
<property name="option" value="EOL"/>
</module>
<module name="SingleSpaceSeparator">
<property name="validateComments" value="false"/>
</module>
<module name="TypecastParenPad"/>
<module name="WhitespaceAfter"/>
<module name="WhitespaceAround"/>

</module>

</module>

Report Generation

Let’s build the project with:

gradlew clean build

The build will fail with a similar error:

* What went wrong:
Execution failed for task ':checkstyleMain'.
> Checkstyle rule violations were found. See the report at: file:///C:/Users/Oleksii/Documents/datamify/projects/development-code-style/build/reports/checkstyle/main.html
Checkstyle files with violations: 1
Checkstyle violations by severity: [warning:8]

As you can see in build/reports/checkstyle requested reports were generated. Let’s open the HTML version to see errors.

This information can be used to fix the errors.

Intellij IDEA Plugin

However, your IDE can help you with the formatting. In this post, Intellij IDEA will be reviewed.

Plugin Installation

To begin with, we should install the Intellij IDEA plugin for checkstyle. It is done in settings. It is called CheckStyle-IDEA.

Configuration

The next step is to apply our configuration file in IntelliJ IDEA. The CheckStyle configuration is selected with our checkstyle.xml.

After that, we just Reformat Code with the menu or hotkeys.

The result is the next reformatted code:

package com.datamify.development.codestyle;public class Tuple {public void doSomething(int
param) {
System.out.println("Param: " + param);
}
}

As you can see, the code is reformatted. However, it is not ideal. Maybe the configuration file should be changed to satisfy your needs. Also, you have to add a Javadoc comment based on this configuration. For your projects, you can remove the rule if you do not need it.

package com.datamify.development.codestyle;/**
* Useful Javadoc.
*/
public class Tuple {
public void doSomething(int
param) {
System.out.println("Param: " + param);
}
}

Running the build with changed code will succeed.

Summary

In this post, CheckStyle was used to validate the source code based on the accepted project style. It can be the first step in CI/CD pipeline. The check will be done automatically. As a result, the review process will be slightly easier.

The source code is available at Github.

Originally published at https://datamify.com on July 24, 2021.

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