How to share POM fragments between different POMs

Question

I am currently struggling with Maven: I have a complex project made of several nested modules and for some of those modules, I have similar configurations in the POMs.

I would like to make it clean. Actually, I would like to define a "runnable-jar" common configuration and activate it in some modules.

Here is the POM fragment I would like to share between several projects:

<build>
    <plugins>
       <plugin>

        <artifactId>maven-assembly-plugin</artifactId>
        <configuration>

            <!-- Use a custom descriptor, with suffix "bin" -->
            <descriptors>
                <descriptor>src/main/assembly/runnable-jar-assembly.xml</descriptor>
            </descriptors>

            <!-- Add main class to manifest -->
            <archive>
                <manifest>
                    <mainClass>${mainClass}</mainClass>
                </manifest>
            </archive>

        </configuration>

        <!-- Add build of this package to lifecycle -->
        <executions>
            <execution>
                <id>make-runnable-jar</id>
                <phase>package</phase>
                <goals>
                    <goal>single</goal>
                </goals>
            </execution>
        </executions>

       </plugin>
    </plugins>
</build>

In some of the POMS, I would like to be able to do something like:

<!-- Set the main class -->
<properties>
    <mainClass>my.main.Class</mainClass>
</properties>

<!-- Activate runnable jar build -->
<import>src/main/pom/runnable-jar-pom.xml</import> 

I have searched for a mean to import some XML fragments into a POM, or to define a whole XML nodeset macro.

For what I have found, the closest solution would be to define a profile in the parent POM and activate it in some sub modules by testing the presence of a file. See this related question. But I am facing the problem of the {basedir} property not being set correctly inherited / set.

I find it very surprising to need a hack to do something so basic (=usual). How do you usually handle this in Maven ?

Answer 1

I have just discovered something that might solve my problem :

A module does not require to be a sub-module of its parent module.

Parent and sub-module relationships are separate concepts.

You can specify a parent POM module that is not the actual parent folder in your folder structure, by using the relativePath attribute (as explained in the doc)

In my case, I use the following layout:

• main-project
  • utils (parent:main-project)
  • cli-programs (parent:main-project)
    • generic-cli (parent:cli-programs; Dummy & empty POM module)
    • cli-1 (parent:generic-cli)
    • cli-2 (parent:generic-cli)

Then, in generic-cli/pom.xml I can declare a configuration that is common to all my cli programs (like custom test suites, runnable-jar packaging, etc).