Question

I have a parent project with 5 children having also dependencies between each other. I used both inheritence with <parent> element in the children pom.xml and aggregation with <module> element in the parent.

My parent pom looks like this:

<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>com.domain</groupId>
<artifactId>Parent</artifactId>
<packaging>pom</packaging>
<version>RELEASE</version>
<name>Parent</name>

<modules>
    <module>../Child1</module>
    <module>../Child2</module>
    <module>../Child3</module>
    <module>../Child4</module>
    <module>../Child5</module>
</modules>

<dependencyManagement>
    <dependencies>
        <dependency>
            <groupId>com.domain</groupId>
            <artifactId>Child1</artifactId>
            <version>RELEASE</version>
        </dependency>
        <dependency>
            <groupId>com.domain</groupId>
            <artifactId>Child2</artifactId>
            <version>RELEASE</version>
        </dependency>
    </dependencies>
</dependencyManagement>
</project>

Child3 pom looks like this:

<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>com.domain</groupId>
<artifactId>Child3</artifactId>
<name>Child3</name>
<packaging>war</packaging>

<parent>
    <artifactId>Parent</artifactId>
    <groupId>com.domain</groupId>
    <version>RELEASE</version>
</parent>

<dependencies>
    <dependency>
        <groupId>com.domain</groupId>
        <artifactId>Child1</artifactId>
    </dependency>
    <dependency>
        <groupId>com.domain</groupId>
        <artifactId>Child2</artifactId>
    </dependency>
</dependencies>
</project>

Everything works fine when I run mvn install on Parent or Child1. But when I run it on Child3 I get the following errors:

[INFO] Failed to resolve artifact.
Missing:
----------
1) com.domain:Child1:jar:RELEASE
...
2) com.domain:Child2:jar:RELEASE

What’s wrong with my set-up?

Answer 1

I won’t really try to solve the issue of your current approach but will rather cover what I consider as the best practice in this case. Feel free to adopt it or not 🙂

First of all, please note that the RELEASE (and LATEST) is a special keyword (not sure you are aware of this) and RELEASE is somehow misused here (a parent with a version defined to RELEASE doesn’t really make sense). Anyway, these special keywords were a bad idea and are deprecated (I’m not sure they’re supported in Maven3) for the sake of build reproducibility, just avoid using them.

So, use a SNAPSHOT version if the project is under active development instead i.e. modify the parent like this:

<project>

  <modelVersion>4.0.0</modelVersion>

  <groupId>com.domain</groupId>
  <artifactId>Parent</artifactId>
  <version>1.0-SNAPSHOT</version>
  <packaging>pom</packaging>

  <name>Parent</name>

  <modules>
    <module>../Child1</module>
    <module>../Child2</module>
    <module>../Child3</module>
    <module>../Child4</module>
    <module>../Child5</module>
  </modules>

</project>

Note that I removed the dependencyManagement element, I don’t think it provides much added value for internal dependencies of a multi module build and recommend using the the ${project.groupId} and ${project.version} built-in properties instead when declaring them:

<project>
  <modelVersion>4.0.0</modelVersion>

  <parent>
    <artifactId>Parent</artifactId>
    <groupId>com.domain</groupId>
    <version>1.0-SNAPSHOT</version><!-- must hard code this -->
  </parent>

  <!--groupId>com.domain</groupId--><!-- you can skip this, you inherit it -->
  <artifactId>Child3</artifactId>
  <packaging>war</packaging>

  <name>Child3</name>

  <dependencies>
    <dependency>
      <groupId>${project.groupId}</groupId>
      <artifactId>Child1</artifactId>
      <version>${project.version}</version>
    </dependency>
    <dependency>
      <groupId>${project.groupId}</groupId>
      <artifactId>Child2</artifactId>
      <version>${project.version}</version>
    </dependency>
  </dependencies>
</project>

As I wrote, I don’t think using dependencyManagement is really useful for internal dependencies and that’s how I setup my projects. But you can if you want. Just use the properties to not repeat information.