Question

I need a variable in my archetype resource files that is a path to the directory where the new project is being generated. This StackOverflow post is from a guy who made his own plugin to do this.

Unfortunately, I can’t figure out how it was originally intended to run. If I run this command:

mvn \
com.example.build.maven:property-setter-maven-plugin:0.1:set-properties \
archetype:generate \
-DarchetypeGroupId=... -DarchetypeArtifactId=... -DarchetypeVersion=... -DartifactId=...

from an empty directory where I intend to create the new project from the archetype I get this error:

Goal requires a project to execute but there is no POM in this directory

This seems completely wrong to me. I’m trying to create a new maven project in this directory, there shouldn’t already be a pom.xml there. So, I looked up the phases run by maven-archetype-plugin and decided to instead run this plugin on <goal>archetype:generate</goal> and I removed the set-properties from the maven command I’m executing.

Now, when I run the archetype:generate command it generates an archetype, but none of the environment variables that I need exist, its as if the plugin is now doing absolutely nothing.

Does anybody know how I can get this to work?

Answer 1

First the simple answer:

Is the custom plugin really needed? The ${basedir} variable should work in archetype resource files which corresponds to the base directory the archetype was run from.

The root of the target project is ${basedir}/${artifactId}, so if my template pom.xml is the following:

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>${groupId}</groupId>
    <artifactId>${artifactId}</artifactId>
    <version>${version}</version>
    <packaging>jar</packaging>

    <name>A custom project at base ${basedir}/${artifactId}</name>

</project>

Then the archetype-generated pom.xml will look something like:

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>galah</groupId>
    <artifactId>galah-artifact</artifactId>
    <version>1.0-SNAPSHOT</version>
    <packaging>jar</packaging>

    <name>A custom project at base /home/prunge/java/testing/galah-artifact</name>

</project>

(assuming I set the groupId, artifactId, version through the command line/prompt)

---

But now let’s assume you need those environment variables for some other reason, not just the base directory of the project.

From what I can tell, the property-setter-maven-plugin takes the current execution properties and puts them in environment variables. And you need the base directory

To get the property-setter-maven-plugin to run, it needs modification since the original requires a project/POM to run as defined in the metadata.

The original MOJO definition:

/**
 * @goal set-properties
 * @phase validate
 * @since 0.1
 */
public class PropertySetterMojo extends AbstractMojo
{
    /**
     * @parameter default-value="${project}"
     * @parameter required
     * @readonly
     */
    private MavenProject project;

    /**
     *  @parameter expression="${session}"
     *  @readonly
     */
    private MavenSession session;

    /**
     * @parameter expression="${mojoExecution}"
     * @readonly
     * @required
     */
    protected MojoExecution execution;

    ...

}

To make it so this plugin can run without a project present, a couple of changes are needed:

• The @requiresProject false, because this is true by default. Additional documentation is here.
• There is a project field of type MavenProject and it is marked as @parameter required – this needs to be removed so that the MOJO can execute without a project. From a casual glance at the source code from the original post this field was not used so can be safely removed.

So you’ll end up with something like:

/**
 * @goal set-properties
 * @phase validate
 * @since 0.1
 * @requiresProject false 
 */
public class PropertySetterMojo extends AbstractMojo
{
    /**
     *  @parameter expression="${session}"
     *  @readonly
     */
    private MavenSession session;

    /**
     * @parameter expression="${mojoExecution}"
     * @readonly
     * @required
     */
    protected MojoExecution execution;

    ...

}

You can then run the command line as you did before:

mvn \
com.example.build.maven:property-setter-maven-plugin:0.1:set-properties \
archetype:generate \
-DarchetypeGroupId=... -DarchetypeArtifactId=... -DarchetypeVersion=... -DartifactId=...

and property-setter-maven-plugin should be able to execute now.