Develop Reference

Maven multi module project, but children have another parent

I encountered a multi module Maven project where the parent defines some child modules in the pom, but some of the child modules reference another parent. Something like this:
parent pom:
<groupId>test</groupId>
<artifactId>parentAAA</artifactId>
<packaging>pom</packaging>
<version>1.0</version>
<modules>
<module>module1</module>
<module>module2</module>
<module>module3</module>
</modules>
module1 pom:
<parent>
<groupId>test</groupId>
<artifactId>parentBBB</artifactId>
<version>2.0</version>
</parent>
<groupId>test</groupId>
<artifactId>module1</artifactId>
<version>1.0</version>
The project builds with maven 3.6.3 but the versions plugin fails.
Is such a configuration correct? (My assumption is that is isn't)

Why can't maven parse the expression in the parent's version?

I came across a problem with a maven project build.
My project structure is as follows
my-message
|
---my-message-api
|
--- my-message-provider
Below is the pom.xml code
my-message.pom
<parent>
<groupId>com.xiaofeng.my</groupId>
<artifactId>my-parent</artifactId>
<version>0.0.1</version>
</parent>
<artifactId>my-message</artifactId>
<version>${my-message.version}</version>
<packaging>pom</packaging>
<name>${project.artifactId}</name>
<properties>
<my-message.version>0.0.1-SNAPSHOT</my-message.version>
</properties>
<modules>
<module>my-message-api</module>
<module>my-message-provider</module>
</modules>
my-message-api.pom
<parent>
<groupId>com.msh.my</groupId>
<artifactId>my-message</artifactId>
<version>${my-message.version}</version>
<relativePath>../pom.xml</relativePath>
</parent>
my-message-provider.pom
<parent>
<groupId>com.msh.my</groupId>
<artifactId>my-message</artifactId>
<version>${my-message.version}</version>
<relativePath>../pom.xml</relativePath>
</parent>
<artifactId>my-message-provider</artifactId>
<dependencies>
<dependency>
<groupId>com.msh.my</groupId>
<artifactId>my-message-api</artifactId>
<version>${my-message.version}</version>
</dependency>
</dependencies>
maven install output
Failed to execute goal on project my-message-provider: Could not resolve dependencies for project
com.msh.my:my-message-provider:jar:0.0.1-SNAPSHOT: Failed to collect dependencies at com.msh.my:my-message-api:jar:0.0.1-SNAPSHOT:
Failed to read artifact descriptor for com.msh.my:my-message-api:jar:0.0.1-SNAPSHOT: Could not find artifact com.msh.my:my-message:pom:${my-message.version}
in nexus (http://nexus_url:8081/nexus/content/groups/public)
Why can't maven parse the expression in the parent's version? please help me

Because you can't use a variable in the specification of a parent in a module. Maven needs to be able to resolve the whole model structure before it can resolve variables.

Unable to use classes of one child module into another in multi-module maven project

I want to use the classes of one child module into another child module present in multi-module maven project. I have followed many existing solution. I am doing exactly same thing as in existing solution. But still it does not works.
Project structure:
Parent A: sampleproject
|-- child A: Gui
|-- child B: calculator
This is how pom.xml of parentA looks like:
<groupId>com.example</groupId>
<artifactId>sampleproject</artifactId>
<version>0.0.1-SNAPSHOT</version>
<packaging>pom</packaging>
<modules>
<module>Gui</module>
<module>calculator</module>
</modules>
pom.xml of child A looks like:
<parent>
<groupId>com.example</groupId>
<artifactId>sampleproject</artifactId>
<version>0.0.1-SNAPSHOT</version>
</parent>
<artifactId>Gui</artifactId>
<packaging>jar</packaging>
<dependencies>
<dependency>
<groupId>${project.groupId}</groupId>
<artifactId>calculator</artifactId>
<version>${project.version}</version>
<type>jar</type>
</dependency>
<dependencies>
pom.xml of child B looks like:
<parent>
<groupId>com.example</groupId>
<artifactId>sampleproject</artifactId>
<version>0.0.1-SNAPSHOT</version>
</parent>
<artifactId>calculator</artifactId>
<packaging>jar</packaging>
When I perform mvn install on parent project. jar files are created in calculator/target/name_of_jar.jar and Gui/target/name_of_jar.jar. But when I check in maven dependencies of Gui project, only directory of calculator is created rather than jar file.
Here is image of maven dependencies in Gui project.
Links I have followed: use-a-class-from-the-other-child-module-in-maven and share-classes-within-modules-in-maven-project

Use of environment variable in POM.xml doesn't work

I am trying to pull out the version number of the POM and all the dependencies to a environment variable. For example:
<project
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven- 4.0.0.xsd"
xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema- instance">
<modelVersion>4.0.0</modelVersion>
<artifactId>example-assembly</artifactId>
<name>example-assembly</name>
<properties>
<current.version>${env.CURRENTVERSION}</current.version>
</properties>
<dependencies>
<dependency>
<groupId>com.example.demo</groupId>
<artifactId>exceptions</artifactId>
<version>${current.version}</version>
</dependency>
<dependencies>
<packaging>war</packaging>
<version>${current.version}</version>
</project>
With the above setup, when I run mvn clean command I am getting following error:
dependencies.dependency.version for example-assembly:war must be a valid version but is '${env.CURRENTVERSION}'
Any idea about what could be the issue?
Note: I am running maven in windows OS

There is a better alternative for updating Versions in pom.xml than using environment variables inside pom.xml: Versions Maven Plugin. This allows you to change pom.xml using maven command line.
Sample scenario
Project Structure:
+ P (Parent - Version 1.0.0-SNAPSHOT)
-- C1 (Child Project 1 - Version 1.0.0-SNAPSHOT)
-- C2 (Child Project 2 - Version 1.0.0-SNAPSHOT also depends on C1)
Task
You want to change version in all pom.xml files to 1.0.1-SNAPSHOT
Parent pom.xml
<project>
<modelVersion>4.0.0</modelVersion>
<groupId>sample</groupId>
<artifactId>p</artifactId>
<version>1.0.0-SNAPSHOT</version>
<name>Parent</name>
<packaging>pom</packaging>
<modules>
<module>c1</module>
<module>c2</module>
</modules>
</project>
Child Project 1 pom.xml
<project>
<modelVersion>4.0.0</modelVersion>
<artifactId>c1</artifactId>
<name>Child Project 1</name>
<packaging>jar</packaging>
<parent>
<groupId>sample</groupId>
<artifactId>p</artifactId>
<version>1.0.0-SNAPSHOT</version>
</parent>
</project>
Child Project 2 pom.xml
<project>
<modelVersion>4.0.0</modelVersion>
<artifactId>c2</artifactId>
<name>Child Project 2</name>
<packaging>jar</packaging>
<parent>
<groupId>sample</groupId>
<artifactId>p</artifactId>
<version>1.0.0-SNAPSHOT</version>
</parent>
<dependencies>
<dependency>
<groupId>sample</groupId>
<artifactId>c1</artifactId>
<version>1.0.0-SNAPSHOT</version>
</dependency>
</dependencies>
</project>
Command
Command to set new version in all pom.xml files
mvn -B -DnewVersion=1.0.1-SNAPSHOT versions:set
In case new version is represented by environment variable CURRENTVERSION
mvn -B -DnewVersion=$CURRENTVERSION versions:set
Here -B means --batch-mode (so new version won't be prompted on console)
Resultant files would be
Parent pom.xml
<project>
<modelVersion>4.0.0</modelVersion>
<groupId>sample</groupId>
<artifactId>p</artifactId>
<version>1.0.1-SNAPSHOT</version>
<name>Parent</name>
<packaging>pom</packaging>
<modules>
<module>c1</module>
<module>c2</module>
</modules>
</project>
Child Project 1 pom.xml
<project>
<modelVersion>4.0.0</modelVersion>
<artifactId>c1</artifactId>
<name>Child Project 1</name>
<packaging>jar</packaging>
<parent>
<groupId>sample</groupId>
<artifactId>p</artifactId>
<version>1.0.1-SNAPSHOT</version>
</parent>
</project>
Child Project 2 pom.xml
<project>
<modelVersion>4.0.0</modelVersion>
<artifactId>c2</artifactId>
<name>Child Project 2</name>
<packaging>jar</packaging>
<parent>
<groupId>sample</groupId>
<artifactId>p</artifactId>
<version>1.0.1-SNAPSHOT</version>
</parent>
<dependencies>
<dependency>
<groupId>sample</groupId>
<artifactId>c1</artifactId>
<version>1.0.1-SNAPSHOT</version>
</dependency>
</dependencies>
</project>

The variable you define has the scope in the same pom.xml only and cannot be used in any other pom.
If you want to define the variable globally define it in settings.xml of maven.
Define the variable env.CURRENTVERSION somewhere in the the same pom, root pom or settings.xml
or else provide the exact version value in its place.
<properties>
<current.version>'your correct version'</current.version>
</properties>
e.g.
<properties>
<current.version>1.0.0</current.version>
</properties>

Maven module hierarchy

I have two modules(maven projects) in parent maven project: android-module and server-module. This two modules uses identical models(POJO - classes). So I want extract models from both modules and make new module in parent project.
So I whant this:
--Project
|--android-module
| -- pom.xml
|--server-module
| -- pom.xml
-- pom.xml
remake to this:
--Project
|--android-module
| -- pom.xml
|--server-module
| -- pom.xml
|--models-module
| -- pom.xml
-- pom.xml
At the same time I want to root pom.xml compiles and build jar from models-module and store jar in my local repository. Then child pom.xml's were taking it from the repository and included in the android and server modules.
Question: How to tell maven to build and store jar in my local repository automatically.
Is it possible? If no - please, give me some ideas.... Thnks

Just run mvn install. This will install the packaged jar into your local repo in ~/.m2
Make sure you run maven from the root pom

The solution is found. It was much easier.
parent pom.xml:
...
<groupId>com.lutshe</groupId>
<artifactId>doiter</artifactId>
<version>1.0-SNAPSHOT</version>
<packaging>pom</packaging>
<modules>
<module>doiter-android</module>
<module>doiter-server</module>
<module>doiter-model</module>
</modules>
...
child1 (android project) pom.xml:
...
<parent>
<groupId>com.lutshe</groupId>
<artifactId>doiter</artifactId>
<version>1.0-SNAPSHOT</version>
</parent>
<groupId>com.lutshe</groupId>
<artifactId>doiter-android</artifactId>
<version>1.0-SNAPSHOT</version>
<packaging>apk</packaging>
<dependencies>
<dependency>
<groupId>com.lutshe</groupId>
<artifactId>doiter-models</artifactId>
<version>1.0-SNAPSHOT</version>
</dependency>
</dependencies>
...
child2 (server) pom.xml:
...
<parent>
<groupId>com.lutshe</groupId>
<artifactId>doiter</artifactId>
<version>1.0-SNAPSHOT</version>
</parent>
<groupId>com.doiter.server</groupId>
<artifactId>doiter-server</artifactId>
<version>0.1.0</version>
<packaging>jar</packaging>
<dependencies>
<dependency>
<groupId>com.lutshe</groupId>
<artifactId>doiter-models</artifactId>
<version>1.0-SNAPSHOT</version>
</dependency>
</dependencies>
...
child3 (shared models) pom.xml:
...
<parent>
<groupId>com.lutshe</groupId>
<artifactId>doiter</artifactId>
<version>1.0-SNAPSHOT</version>
</parent>
<groupId>com.lutshe</groupId>
<artifactId>doiter-model</artifactId>
<version>1.0-SNAPSHOT</version>
...