Question

I’m creating a Maven archetype which generates a project skeleton that
will include a dependency on the project from which the archetype
originated.

For example, the origin project looks like:

origin/archetype/... archetype for generating project 
      /core/... core services 
      /extra/... extra services 

and the archetype will generate a project with a POM that contains
dependencies like so:

<dependencies> 
  <dependency> 
    <groupId>com.foo</groupId> 
    <artifactId>origin-core</artifactId> 
    <version>SOMEVERSION</code> 
  </dependency> 
</dependencies> 

I want SOMEVERSION to be the version of the origin project at the time
that the archetype is built and installed into the repository.

So if the origin project is at version 1.0-SNAPSHOT and is mvn
installed, then I want the archetype to generate a dependency on
origin-core 1.0-SNAPSHOT. And when the origin project is released, and automatically
bumped to version 1.0, I want the archetype to generate a dependency on
origin-core 1.0.

Basically I’d like to use ${archetypeVersion} as a Velocity variable in the archetype
POM, but that doesn’t seem possible.

Is there any other way of accomplishing what I’m trying to do here?

Answer 1

I asked the above question on the Maven mailing list a few days ago and got tumbleweeds. Fortunately, I eventually figured it out on my own. Here’s at least one sane way to accomplish this:

Use Maven filtering on your src/main/resources/archetype-resources/pom.xml file to substitute in the current project version when building the archetype.

Here’s how that’s done:

Modify your archetype/pom.xml file to enable filtering on the archetype-resources/pom.xml file and not on anything else (because your archetype files will naturally have ${variable}s all over the place and you don’t want those to be substituted at build time, you want them to be substituted when the archetype is created).

<resources>
  <resource>
    <directory>src/main/resources</directory>
    <filtering>true</filtering>
    <includes>
      <include>archetype-resources/pom.xml</include>
    </includes>
  </resource>
  <resource>
    <directory>src/main/resources</directory>
    <filtering>false</filtering>
    <excludes>
      <exclude>archetype-resources/pom.xml</exclude>
    </excludes>
  </resource>
</resources>

Enable an escape character for use when filtering, so that you can escape all the variables in your archetype pom that need to remain as-is so that they can be substituted at archetype generation time:

<pluginManagement>
  <plugins>
    ...
    <plugin>
      <groupId>org.apache.maven.plugins</groupId>
      <artifactId>maven-resources-plugin</artifactId>
      <version>2.5</version>
      <configuration>
        <escapeString>\</escapeString>
      </configuration>
    </plugin>
  </plugins>
</pluginManagement>

(Note the <resources> and <pluginManagement> elements shown above should be placed inside the <build> element of your POM.)

Use ${project.version} in your archetype pom, where you want the version of your archetype project to be inserted, and escape all of the other variables that should remain unsubstituted until archetype generation time:

<?xml version="1.0" encoding="UTF-8"?>
<project ...>
  <modelVersion>4.0.0</modelVersion>

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

  <dependencies>
    <dependency>
      <groupId>com.foo</groupId>
      <artifactId>origin-core</artifactId>
      <version>${project.version}</version>
    </dependency>
  </dependencies>

</project>