JBoss Parent POM

The parent Maven POM for JBoss community projects.

What is it?

The JBoss parent POM provides default configuration for Maven builds.

Recommended/Default versions for the most commonly used Maven plugins
Manifest configuration for the jar and assembly plugins
Profiles for generating source jars, and enforcing a minimum versions of Java and Maven
Distribution Management and other configuration for deploying to the JBoss.org Maven repositories

How to use it?

Start out by adding the parent configuration to your pom.

<parent>
  <groupId>org.jboss</groupId>
  <artifactId>jboss-parent</artifactId>
  <version>40</version>
  <!-- The empty relativePath makes Maven look it up in the repository. Missing tag default is ../pom.xml. -->
  <relativePath/>
</parent>

The pom includes properties which allow various build configuration to be customized. For example, to override the default version of the maven-compiler-plugin, just set a property.

<properties>
  <version.compiler.plugin>3.1</version.compiler.plugin>
</properties>

Or override the default Java compiler source and target level used in the build. Note the default level is 11. Also note that the preferred way to set the source/target version for compilation is to use one of the build-release-XXX control files instead, which will set the javac --release flag to the corresponding version.

<properties>
  <maven.compiler.target>17</maven.compiler.target>
  <maven.compiler.source>17</maven.compiler.source>
</properties>

The minimum version of Java or Maven required to run a build can also be set via properties.

<properties>
  <maven.min.version>3.9.0</maven.min.version>
  <jdk.min.version>17</jdk.min.version>
</properties>

If jdk.min.version is not set, it defaults to the version defined by the maven.compiler.source property.

For the full list of properties, refer to the POM itself.

The JBoss Release Profile

The parent POM includes a Maven profile called jboss-release. This profile contains settings for generating a full project source archive, javadoc jar files, and release deployment metadata. If using the Maven release plugin, this profile will automatically be activate during the release:perform step.

If the Maven release plugin is not used during the release process, the profile can be manually activated from the command line during a release build.

mvn -Pjboss-release deploy

The GPG Sign Profile

This POM includes a Maven profile called "gpg-sign" which provides default configuration to generate GPG signatures for the build artifacts.

mvn -Pgpg-sign deploy

In order for the gpg plugin to properly create a signature for each artifact, the properties gpg.keyname and gpg.passphrase must be available to the current build. These properties can either be set in a build profile, or on the command line.

<profile>
  <id>gpg-config</id>
  <properties>
    <gpg.keyname>me@home.com</gpg.keyname>
    <!-- Don't keep passphrase in plain text! -->
    <gpg.passphrase>secret</gpg.passphrase>
  </properties>
</profile>

Multi-Release JARs

Starting with version 30, the JBoss Parent POM provides a framework for multi-release JAR build and test.

Functional overview

The multi-release JAR support works in two parts: compilation and testing.

Compilation

Compilation works by providing extra executions of the compiler plugin in order to build the additional JAR layers. The base layer is built by the standard default-compile execution. After that, Maven profiles are activated based on the presence of extra layer source directories (e.g. src/main/java12, src/main/java16 etc.). These profiles contain additional executions of the compiler plugin which compile the sources in the layer directory, while putting the output of the previous step on the class path.

Each present layer is in turn compiled with the results of all the previous layers on the classpath in the correct order. The additional layer class files are output under the target/classes directory in the appropriate location for multi-release JAR layers.

In order to select the correct class files for the given Java version, the <release> property is used. This prevents accidental usage of APIs which are only present in later versions than the one being compiled.

Testing

Testing using maven-surefire-plugin is supported by running the project unit tests on every supported Java version. In order to do so, it is expected that the following system property or properties are set as needed:

java11.home: this property must be set to the location of a Java 11 JDK installation
java17.home: this property must be set to the location of a Java 17 JDK installation
java21.home: this property must be set to the location of a Java 21 JDK installation

In order to simplify development, it is recommended to project maintainers to set these properties in your personal Maven settings.xml file.

Extra unit tests are run for a given platform whenever a newer version than that platform was used to build the project and the appropriate control file is found (see Build control files reference).

Configuration

To configure a multi-release JAR, you need the following pieces of information:

The minimum (oldest) version of Java that will be supported by the project
The maximum (newest) version of Java for which your project has sources

Step 1: Base layer version

Choose your base layer version. This can be Java 11 or anything later. Configure the version by configuring the release property in the default-compile execution of maven-compiler-plugin:

<plugin>
  <artifactId>maven-compiler-plugin</artifactId>
  <executions>
    <execution>
      <id>default-compile</id>
      <configuration>
        <release>17</release>
      </configuration>
    </execution>
  </executions>
</plugin>

If the build-release-11, build-release-17, or build-release-21 file is present in the root of your project, then this step is automatically done for you. Only one such file should be present.

Step 2: Highest layer version

Configure the jdk.min.version property as described above to match either:

The maximum (newest) Java version for which sources exist in your project, or
Some Java version higher than that

This is the version of Java that will build all of your layers, so it necessarily must be able to compile every version of Java sources from oldest to newest.

Step 3: Source directories

The sources for your base layer continue to reside in src/main/java and src/test/java.

Additional layers are in directories whose names correspond to the version of Java that is targeted by that directory. For example, sources which are specific to Java 13 and later would be in src/main/java13, whereas sources which are specific to Java 16 and later would be in src/main/java16.

If you have a class that needs an alternative implementation for a given Java version, you only need to provide the replacement source file in the directory corresponding to the oldest version that supports the alternative source. It is not necessary to copy identical classes into more than one layer; doing so will increase the size of the resultant artifact needlessly.

There are restrictions on these directories. You may only provide sources that correspond to sources that exist in the base layer - that is, it is a violation of the MR JAR specification to provide sources that introduce new APIs only in later Java versions. The JDK does enforce this at run time. In addition, providing additional public members in later versions is generally not recommended.

Using MR JAR functions with GitHub Actions

Using this functionality with GitHub Actions is relatively simple. It entails adding the additional JDK version(s) by way of a setup action, and then passing the location of each additional JDK to the build.

As an example, for a project that is built on Java 17 but must also be tested against JDK 11 your build.yml might look something like this:

jobs:
  build:
    runs-on: ubuntu-latest
    name: Build using Maven

    steps:
      - uses: actions/checkout@v2
        name: Checkout

      - uses: actions/setup-java@v3
        name: Set up JDKs
        with:
          distribution: temurin
          java-version: |
            11
            17

      - name: Build
        run: mvn -B verify --file pom.xml "-Djava11.home=${{env.JAVA_HOME_11_X64}}"

Note that this configuration causes the default JAVA_HOME environment to be set to JDK 17.

Build control files reference

These build control files are tested only for their presence. They do not need to have any content (i.e. they can be zero-sized).

File name	Purpose	Reference
`build-release-11`	Use the `<release>` option to set Java 11 for the base layer.	Step 1: Base layer version
`build-release-17`	Use the `<release>` option to set Java 17 for the base layer.	Step 1: Base layer version
`build-release-21`	Use the `<release>` option to set Java 21 for the base layer.	Step 1: Base layer version
`build-test-java11`	Run tests for Java 11 when `java11.home` is set and JDK 12 or later is used.	Testing
`build-test-java17`	Run tests for Java 17 when `java17.home` is set and JDK 18 or later is used.	Testing
`build-test-java21`	Run tests for Java 21 when `java21.home` is set and JDK 22 or later is used.	Testing

Where to get more information?

The github wiki provides some additional examples. For questions/suggestions about the jboss-parent-pom, head to the JBoss Community Build space on the jboss.org site. Issues related to the jboss-parent-pom can be submitted to the JBoss build jira project