maven-plugins

Maven Plugins ⬆

Directory maven-plugins\ contains Maven plugin examples found on the Web or written by ourself. Our final objective to compile Scala source files from a POM file using the Maven command line tool.

In the past years at least two Maven plugins for Scala have been developed, i.e. David's scala-maven-plugin and the outdated plugin maven-scala-plugin (February 2011).

We were no satisfied with the above plugins and decided in late 2018 to write our own Maven plugin for compiling ¹ the Scala source files of our Scala projects (see for instance examples\README.md).

☛ Plugin naming convention
The Maven Guide to Developing Java Plugins starts with an important notice that recommand us to name our plugin <yourplugin>-maven-plugin.

first-maven-plugin

This plugin project is adapted from the code example presented in section 11.4 – Writing a Custom Plugin – of the online book Maven: The Complete Reference.

The project is organized as follows:

> tree /a /f . |findstr /v /b [A-Z]
|   00download.txt
|   build.bat
|   pom.xml
|
+---src
    \---main
        \---java
            \---org
                \---sonatype
                    \---plugins
                             EchoMojo.java

WIP ²

hello-maven-plugin

The plugin project hello-maven-plugin is the code example presented in the online Maven Guide to Developing Java Plugins.

The project is organized as follows :

> tree /a /f . |findstr /v /b [A-Z]
|   00download.txt
|   install-local.bat
|   pom.xml
|
+---src
|   \---main
|       +---java
|           \---sample
|               \---plugin
|                       GreetingMojo.java
\---test
    |   test\pom.xml
    \---src
        \---main
            +---java
                    Dummy.java

WIP

scala-maven-plugin

We started this project in late 2018; we use scala-maven-plugin in all Scala projects of our GitHub repository michelou/dotty-examples (but not only).

scala-maven-plugin features two goals with parameters similar to the maven-compiler-plugin:

Goal	Parameters
compile	additionalClasspathElements addOutputToClasspath compilerArgs excludes includes
run	jvmArgs

The project is organized as follows :

> tree /a /f . |findstr /v /b [A-Z]
|   pom.xml
|
+---src
    \---main
        \---java
            \---ch
                \---epfl
                    \---alumni
                            HelpMojo.java
                            ScalaAbstractMojo.java
                            ScalaCompileMojo.java
                            ScalaRunMojo.java

Command mvn package generates the JAR file scala-maven-plugin-1.0.0.jar to be deployed as Maven artifact :

> mvn clean compile package
[INFO] Scanning for projects...
[...]
[INFO] java-javadoc mojo extractor found 0 mojo descriptor.
[INFO] bsh mojo extractor found 0 mojo descriptor.
[INFO] ant mojo extractor found 0 mojo descriptor.
[INFO] java-annotations mojo extractor found 3 mojo descriptors.
[...]
 
> dir /b target\*.jar
scala-maven-plugin-1.0.0.jar

Command mvn deploy:deploy-file installs the Maven artifact for our plugin into our local Maven repository %USERPROFILE%\.m2\repository\ :

> mvn deploy:deploy-file -DgroupId=ch.epfl.alumni -DartifactId=scala-maven-plugin -Dversion=1.0.0 -Durl=file://%USERPROFILE%/.m2/repository -DupdateReleaseInfo=true -Dfile=.\target\scala-maven-plugin-1.0.0.jar -Dpackaging=jar -DpomFile=.\pom.xml -DgeneratePom=true -DcreateChecksum=true
[INFO] Scanning for projects...
[...]

☛ scala-maven-plugin Installation
A user has currently two possibilities to install scala-maven-plugin:

• Download our source project, generate and install the plugin as described above.
• Download and extract the Zip file scala-maven-plugin-1.0.zip into the local Maven repository.

The plugin installation should look as follows :

> tree /a /f %USERPROFILE%\.m2\repository\ch\epfl\alumni |findstr /v /b [A-Z]
\---scala-maven-plugin
    |   maven-metadata-remote-repository.xml
    |   maven-metadata-remote-repository.xml.sha1
    |   maven-metadata.xml
    |   maven-metadata.xml.md5
    |   maven-metadata.xml.sha1
    |   resolver-status.properties
    |
    \---1.0.0
            scala-maven-plugin-1.0.0.jar
            scala-maven-plugin-1.0.0.jar.md5
            scala-maven-plugin-1.0.0.jar.sha1
            scala-maven-plugin-1.0.0.pom
            scala-maven-plugin-1.0.0.pom.md5
            scala-maven-plugin-1.0.0.pom.sha1

Footnotes

[1] pom.xml ↩

We give here the <plugin> section of a POM file.

<plugin>
    <groupId>ch.epfl.alumni</groupId>
    <artifactId>scala-maven-plugin</artifactId>
    <version>${scala.maven.version}</version>
    <executions>
        <execution>
            <id>scala-compile</id>
            <phase>compile</phase>
            <goals>
                <goal>compile</goal>
            </goals>
            <configuration>
                <additionalClasspathElements>
                    <additionalClasspathElement>${m2.hamcrest.jar}</additionalClasspathElement>
                    <!-- ...more additions.. -->
                </additionalClasspathElements>
                <includes>
                    <include>scala/**/*.scala</include>
                </includes>
                <installDirectory>${env.SCALA3_HOME}
            </configuration>
        </execution>
        <!-- ...execution of "run" goal... -->
    </executions>
    <configuration>
        <scalaVersion>${scala.version}</scalaVersion>
        <localInstall>${scala.local.install}</localInstall>
        <!-- <debug>true</debug> -->
        <jvmArgs>
            <jvmArg>-Xms64m</jvmArg>
            <jvmArg>-Xmx1024m</jvmArg>
        </jvmArgs>
    </configuration>
</plugin>

[2] META-INF/maven/plugin.xml ↩

<plugin>
  <name>Sample Parameter-less Maven Plugin</name>
  <description></description>
  <groupId>sample.plugin</groupId>
  <artifactId>hello-maven-plugin</artifactId>
  <version>1.0-SNAPSHOT</version>
  <goalPrefix>hello</goalPrefix>
  <isolatedRealm>false</isolatedRealm>
  <inheritedByDefault>true</inheritedByDefault>
  <mojos>
    <mojo>
      <goal>sayhi</goal>
      <description>Says "Hi" to the user.</description>
      <requiresDirectInvocation>false</requiresDirectInvocation>
      <requiresProject>true</requiresProject>
      <requiresReports>false</requiresReports>
      <aggregator>false</aggregator>
      <requiresOnline>false</requiresOnline>
      <inheritedByDefault>true</inheritedByDefault>
      <implementation>sample.plugin.GreetingMojo</implementation>
      <language>java</language>
      <instantiationStrategy>per-lookup</instantiationStrategy>
      <executionStrategy>once-per-session</executionStrategy>
      <threadSafe>false</threadSafe>
      <parameters/>
    </mojo>
  </mojos>
  <dependencies/>
</plugin>

---

mics/April 2023 ▲