Kotlin Help

Maven

To generate documentation for a Maven-based project, you can use the Maven plugin for Dokka.

You can play around with Dokka and see how it can be configured for a Maven project by visiting our Maven example project.

Apply Dokka

To apply Dokka, you need to add dokka-maven-plugin to the plugins section of your POM file:

<build> <plugins> <plugin> <groupId>org.jetbrains.dokka</groupId> <artifactId>dokka-maven-plugin</artifactId> <version>1.7.20</version> <executions> <execution> <phase>pre-site</phase> <goals> <goal>dokka</goal> </goals> </execution> </executions> </plugin> </plugins> </build>

Generate documentation

The following goals are provided by the Maven plugin:

Goal

Description

dokka:dokka

Generates documentation with Dokka plugins applied. HTML format by default.

Experimental

Goal

Description

dokka:javadoc

Generates documentation in Javadoc format.

dokka:javadocJar

Generates a javadoc.jar file that contains documentation in Javadoc format.

Other output formats

By default, the Maven plugin for Dokka builds documentation in HTML output format.

All other output formats are implemented as Dokka plugins. In order to generate documentation in the desired format, you have to add it as a Dokka plugin to the configuration.

For example, to use the experimental GFM format, you have to add gfm-plugin artifact:

<plugin> <groupId>org.jetbrains.dokka</groupId> <artifactId>dokka-maven-plugin</artifactId> ... <configuration> <dokkaPlugins> <plugin> <groupId>org.jetbrains.dokka</groupId> <artifactId>gfm-plugin</artifactId> <version>1.7.20</version> </plugin> </dokkaPlugins> </configuration> </plugin>

With this configuration, running the dokka:dokka goal produces documentation in GFM format.

To learn more about Dokka plugins, see Dokka plugins.

Build javadoc.jar

If you want to publish your library to a repository, you may need to provide a javadoc.jar file that contains API reference documentation of your library.

For example, if you want to publish to Maven Central, you must supply a javadoc.jar alongside your project. However, not all repositories have that rule.

Unlike the Gradle plugin for Dokka, the Maven plugin comes with a ready-to-use dokka:javadocJar goal. By default, it generates documentation in Javadoc output format in thetarget folder.

If you are not satisfied with the built-in goal or want to customize the output (for example, you want to generate documentation in HTML format instead of Javadoc), similar behavior can be achieved by adding the Maven JAR plugin with the following configuration:

<plugin> <groupId>org.apache.maven.plugins</groupId> <artifactId>maven-jar-plugin</artifactId> <version>3.3.0</version> <executions> <execution> <goals> <goal>test-jar</goal> </goals> </execution> <execution> <id>dokka-jar</id> <phase>package</phase> <goals> <goal>jar</goal> </goals> <configuration> <classifier>dokka</classifier> <classesDirectory>${project.build.directory}/dokka</classesDirectory> <skipIfEmpty>true</skipIfEmpty> </configuration> </execution> </executions> </plugin>

The documentation and the .jar archive for it are then generated by running dokka:dokka and jar:jar@dokka-jar goals:

mvn dokka:dokka jar:jar@dokka-jar

Configuration example

Maven's plugin configuration block can be used to configure Dokka.

Here is an example of a basic configuration that only changes the output location of your documentation:

<plugin> <groupId>org.jetbrains.dokka</groupId> <artifactId>dokka-maven-plugin</artifactId> ... <configuration> <outputDir>${project.basedir}/target/documentation/dokka</outputDir> </configuration> </plugin>

Configuration options

Dokka has many configuration options to tailor your and your reader's experience.

Below are some examples and detailed descriptions for each configuration section. You can also find an example with all configuration options applied at the bottom of the page.

General configuration

<plugin> <groupId>org.jetbrains.dokka</groupId> <artifactId>dokka-maven-plugin</artifactId> <!-- ... --> <configuration> <skip>false</skip> <moduleName>${project.artifactId}</moduleName> <outputDir>${project.basedir}/target/documentation</outputDir> <failOnWarning>false</failOnWarning> <suppressObviousFunctions>true</suppressObviousFunctions> <suppressInheritedMembers>false</suppressInheritedMembers> <offlineMode>false</offlineMode> <sourceDirectories> <dir>${project.basedir}/src</dir> </sourceDirectories> <documentedVisibilities> <visibility>PUBLIC</visibility> <visibility>PROTECTED</visibility> </documentedVisibilities> <reportUndocumented>false</reportUndocumented> <skipDeprecated>false</skipDeprecated> <skipEmptyPackages>true</skipEmptyPackages> <suppressedFiles> <file>/path/to/dir</file> <file>/path/to/file</file> </suppressedFiles> <jdkVersion>8</jdkVersion> <languageVersion>1.7</languageVersion> <apiVersion>1.7</apiVersion> <noStdlibLink>false</noStdlibLink> <noJdkLink>false</noJdkLink> <includes> <include>packages.md</include> <include>extra.md</include> </includes> <classpath>${project.compileClasspathElements}</classpath> <samples> <dir>${project.basedir}/samples</dir> </samples> <sourceLinks> <!-- Separate section --> </sourceLinks> <externalDocumentationLinks> <!-- Separate section --> </externalDocumentationLinks> <perPackageOptions> <!-- Separate section --> </perPackageOptions> </configuration> </plugin>
skip

Whether to skip documentation generation.

Default: false

moduleName

The display name used to refer to the project/module. It's used for the table of contents, navigation, logging, etc.

Default: {project.artifactId}

outputDir

The directory to where documentation is generated, regardless of format.

Default: {project.basedir}/target/dokka

failOnWarning

Whether to fail documentation generation if Dokka has emitted a warning or an error. The process waits until all errors and warnings have been emitted first.

This setting works well with reportUndocumented.

Default: false

suppressObviousFunctions

Whether to suppress obvious functions.

A function is considered to be obvious if it is:

  • Inherited from kotlin.Any, Kotlin.Enum, java.lang.Object or java.lang.Enum, such as equals, hashCode, toString.

  • Synthetic (generated by the compiler) and does not have any documentation, such as dataClass.componentN or dataClass.copy.

Default: true

suppressInheritedMembers

Whether to suppress inherited members that aren't explicitly overridden in a given class.

Note: This can suppress functions such as equals/hashCode/toString, but cannot suppress synthetic functions such as dataClass.componentN and dataClass.copy. Use suppressObviousFunctions for that.

Default: false

offlineMode

Whether to resolve remote files/links over your network.

This includes package-lists used for generating external documentation links. For example, to make classes from the standard library clickable.

Setting this to true can significantly speed up build times in certain cases, but can also worsen documentation quality and user experience. For example, by not resolving class/member links from your dependencies, including the standard library.

Note: You can cache fetched files locally and provide them to Dokka as local paths. See externalDocumentationLinks section.

Default: false

sourceDirectories

The source code roots to be analyzed and documented. Acceptable inputs are directories and individual .kt/.java files.

Default: {project.compileSourceRoots}

documentedVisibilities

The set of visibility modifiers that should be documented.

This can be used if you want to document protected/internal/private declarations, as well as if you want to exclude public declarations and only document internal API.

Can be configured on per-package basis.

Default: PUBLIC

reportUndocumented

Whether to emit warnings about visible undocumented declarations, that is declarations without KDocs after they have been filtered by documentedVisibilities and other filters.

This setting works well with failOnWarning.

This can be overridden at package level.

Default: false

skipDeprecated

Whether to document declarations annotated with @Deprecated.

This can be overridden at package level.

Default: false

skipEmptyPackages

Whether to skip packages that contain no visible declarations after various filters have been applied.

For example, if skipDeprecated is set to true and your package contains only deprecated declarations, it is considered to be empty.

Default: true

suppressedFiles

The directories or individual files that should be suppressed, meaning that declarations from them are not documented.

jdkVersion

The JDK version to use when generating external documentation links for Java types.

For example, if you use java.util.UUID in some public declaration signature, and this option is set to 8, Dokka generates an external documentation link to JDK 8 Javadocs for it.

Default: JDK 8

languageVersion

The Kotlin language version used for setting up analysis and @sample environment.

By default, the latest language version available to Dokka's embedded compiler is used.

apiVersion

The Kotlin API version used for setting up analysis and @sample environment.

By default, it is deduced from languageVersion.

noStdlibLink

Whether to generate external documentation links that lead to the API reference documentation of Kotlin's standard library.

Note: Links are generated when noStdLibLink is set to false.

Default: false

noJdkLink

Whether to generate external documentation links to JDK's Javadocs.

The version of JDK Javadocs is determined by the jdkVersion option.

Note: Links are generated when noJdkLink is set to false.

Default: false

includes

A list of Markdown files that contain module and package documentation

The contents of specified files are parsed and embedded into documentation as module and package descriptions.

classpath

The classpath for analysis and interactive samples.

This is useful if some types that come from dependencies are not resolved/picked up automatically. This option accepts both .jar and .klib files.

Default: {project.compileClasspathElements}

samples

A list of directories or files that contain sample functions which are referenced via @sample KDoc tag.

The sourceLinks configuration block allows you to add a source link to each signature that leads to the url with a specific line number. (The line number is configurable by setting lineSuffix).

This helps readers to find the source code for each declaration.

For an example, see the documentation for the count() function in kotlinx.coroutines.

<plugin> <groupId>org.jetbrains.dokka</groupId> <artifactId>dokka-maven-plugin</artifactId> <!-- ... --> <configuration> <sourceLinks> <link> <path>${project.basedir}/src</path> <url>https://github.com/kotlin/dokka/tree/master/src</url> <lineSuffix>#L</lineSuffix> </link> </sourceLinks> </configuration> </plugin>
path

The path to the local source directory. The path must be relative to the root of the current module.

url

The URL of the source code hosting service that can be accessed by documentation readers, like GitHub, GitLab, Bitbucket, etc. This URL is used to generate source code links of declarations.

lineSuffix

The suffix used to append source code line number to the URL. This helps readers navigate not only to the file, but to the specific line number of the declaration.

The number itself is appended to the specified suffix. For example, if this option is set to #L and the line number is 10, the resulting URL suffix is #L10.

Suffixes used by popular services:

  • GitHub: #L

  • GitLab: #L

  • Bitbucket: #lines-

The externalDocumentationLink block allows the creation of links that lead to the externally hosted documentation of your dependencies.

For example, if you are using types from kotlinx.serialization, by default they are unclickable in your documentation, as if they are unresolved. However, since the API reference documentation for kotlinx.serialization is built by Dokka and is published on kotlinlang.org, you can configure external documentation links for it. Thus allowing Dokka to generate links for types from the library, making them resolve successfully and clickable.

By default, external documentation links for Kotlin standard library and JDK are configured.

<plugin> <groupId>org.jetbrains.dokka</groupId> <artifactId>dokka-maven-plugin</artifactId> <!-- ... --> <configuration> <externalDocumentationLinks> <link> <url>https://kotlinlang.org/api/kotlinx.serialization/</url> <packageListUrl>file:/${project.basedir}/serialization.package.list</packageListUrl> </link> </externalDocumentationLinks> </configuration> </plugin>
url

The root URL of documentation to link to. It must contain a trailing slash.

Dokka does its best to automatically find the package-list for the given URL, and link declarations together.

If automatic resolution fails or if you want to use locally cached files instead, consider setting the packageListUrl option.

packageListUrl

The exact location of a package-list. This is an alternative to relying on Dokka automatically resolving it.

Package lists contain information about the documentation and the project itself, such as module and package names.

This can also be a locally cached file to avoid network calls.

Package options

The perPackageOptions configuration block allows setting some options for specific packages matched by matchingRegex.

<plugin> <groupId>org.jetbrains.dokka</groupId> <artifactId>dokka-maven-plugin</artifactId> <!-- ... --> <configuration> <perPackageOptions> <packageOptions> <matchingRegex>.*api.*</matchingRegex> <suppress>false</suppress> <reportUndocumented>false</reportUndocumented> <skipDeprecated>false</skipDeprecated> <documentedVisibilities> <visibility>PUBLIC</visibility> <visibility>PRIVATE</visibility> <visibility>PROTECTED</visibility> <visibility>INTERNAL</visibility> <visibility>PACKAGE</visibility> </documentedVisibilities> </packageOptions> </perPackageOptions> </configuration> </plugin>
matchingRegex

The regular expression that is used to match the package.

Default: .*

suppress

Whether this package should be skipped when generating documentation.

Default: false

documentedVisibilities

The set of visibility modifiers that should be documented.

This can be used if you want to document protected/internal/private declarations within this package, as well as if you want to exclude public declarations and only document internal API.

Default: PUBLIC

skipDeprecated

Whether to document declarations annotated with @Deprecated.

This can be set on project/module level.

Default: false

reportUndocumented

Whether to emit warnings about visible undocumented declarations, that is declarations without KDocs after they have been filtered by documentedVisibilities and other filters.

This setting works well with failOnWarning.

Default: false

Complete configuration

Below you can see all the possible configuration options applied at the same time.

<plugin> <groupId>org.jetbrains.dokka</groupId> <artifactId>dokka-maven-plugin</artifactId> <!-- ... --> <configuration> <skip>false</skip> <moduleName>${project.artifactId}</moduleName> <outputDir>${project.basedir}/target/documentation</outputDir> <failOnWarning>false</failOnWarning> <suppressObviousFunctions>true</suppressObviousFunctions> <suppressInheritedMembers>false</suppressInheritedMembers> <offlineMode>false</offlineMode> <sourceDirectories> <dir>${project.basedir}/src</dir> </sourceDirectories> <documentedVisibilities> <visibility>PUBLIC</visibility> <visibility>PRIVATE</visibility> <visibility>PROTECTED</visibility> <visibility>INTERNAL</visibility> <visibility>PACKAGE</visibility> </documentedVisibilities> <reportUndocumented>false</reportUndocumented> <skipDeprecated>false</skipDeprecated> <skipEmptyPackages>true</skipEmptyPackages> <suppressedFiles> <file>/path/to/dir</file> <file>/path/to/file</file> </suppressedFiles> <jdkVersion>8</jdkVersion> <languageVersion>1.7</languageVersion> <apiVersion>1.7</apiVersion> <noStdlibLink>false</noStdlibLink> <noJdkLink>false</noJdkLink> <includes> <include>packages.md</include> <include>extra.md</include> </includes> <classpath>${project.compileClasspathElements}</classpath> <samples> <dir>${project.basedir}/samples</dir> </samples> <sourceLinks> <link> <path>${project.basedir}/src</path> <url>https://github.com/kotlin/dokka/tree/master/src</url> <lineSuffix>#L</lineSuffix> </link> </sourceLinks> <externalDocumentationLinks> <link> <url>https://kotlinlang.org/api/latest/jvm/stdlib/</url> <packageListUrl>file:/${project.basedir}/stdlib.package.list</packageListUrl> </link> </externalDocumentationLinks> <perPackageOptions> <packageOptions> <matchingRegex>.*api.*</matchingRegex> <suppress>false</suppress> <reportUndocumented>false</reportUndocumented> <skipDeprecated>false</skipDeprecated> <documentedVisibilities> <visibility>PUBLIC</visibility> <visibility>PRIVATE</visibility> <visibility>PROTECTED</visibility> <visibility>INTERNAL</visibility> <visibility>PACKAGE</visibility> </documentedVisibilities> </packageOptions> </perPackageOptions> </configuration> </plugin>

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Last modified: 27 January 2023