Igor Kromin |   Consultant. Coder. Blogger. Tinkerer. Gamer.

Back in 2015 I wrote about getting around Maven's parent-child project version dependency issue, that was with Maven 3.2.2. Now that Maven 3.5 has been released the same approach doesn't work so I had to rethink how to handle my submodule builds going forward.

Update (19-Jun-2017) - After looking at this more and reading through Maven CI Friendly Versions I've updated this post to reflect how this should be done with Maven 3.5.

My new approach is to set up the parent POM as follows (this actually stays the same as in my previous post):
 Parent POM
<?xml version="1.0" encoding="UTF-8" ?>
<project xmlns="http://maven.apache.org/POM/4.0.0">
<modelVersion>4.0.0</modelVersion>
<groupId>maven.test1</groupId>
<artifactId>maven-test1-parent</artifactId>
<version>${revision}</version> <!-- update 19-Jun-2017 - this is not changed -->
<properties>
<revision>42.0</revision>
</properties>
<name>${project.artifactId}</name>
<description>Main POM file for ${project.artifactId}</description>
<packaging>pom</packaging>
<modules>
<module>Child1</module>
</modules>
</project>


The difference to the previous approach being that the project.version is set to a constant "1.0", but I am still keeping the "revision" property set to "42.0" as before (however this is more or less just a default value now if no revision is specified on the command line, see below).

Update (19-Jun-2017) - the parent POM doesn't change.

The child/sub-module POM now changes to this:
 Child POM
<?xml version="1.0" encoding="UTF-8" ?>
<project xmlns="http://maven.apache.org/POM/4.0.0">
<modelVersion>4.0.0</modelVersion>
<parent>
<groupId>maven.test1</groupId>
<artifactId>maven-test1-parent</artifactId>
<version>${revision}</version> <!-- this is changed from [1.0,99.0) to ${revision} -->
</parent>
<artifactId>maven-test1-child1</artifactId>
<name>${project.artifactId}</name>
</project>




The parent reference now gets a constant version string, but the version of the module itself is still variable and easy to set via the parent POM file. The only down side of this is that if the parent POM changes, you would have to update all of the modules to reference the new parent version, this should be manageable though since parent POM changes should be rare.

Update (19-Jun-2017) - the parent reference is now ${revision} and since the parent POM sets its version to ${revision} as well, the child POM will inherit that.

So this approach still lets you version your modules from one place and removes the need to use the hack-ey parent version range string. This also works in Maven 3.3.3.

Also since the ${revision} property can be set via the command line, there is no need to update the parent POM whenever the revision for the build changes, you can just do this:
 Command
mvn clean install -Drevision=42.1


-i

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