I know it's mauvais ton to ask twice in a single day but here's another Maven puzzler:
I have a parent POM which defines 5 modules (5 subprojects). Since each module is executed in exactly the same way I pull <profile><build> section into the parent POM to get rid of the duplicate code. Now - if I execute build individually from each module it works, however if I want to build all modules at once and move to the parent directory I got error since the very first thing Maven tries to execute is the parent project itself:
mvn package -P release
[INFO] Scanning for projects...
[INFO] Reactor build order:
[INFO] DWD Parent project
[INFO] Projects
After that build fails because exec plugin tries to execute something that is not there. Looking at the output it is pretty obvious that reactor plugin is driving the build but how can I configure reactor to skip the parent?
P.S. To prevent confusion - I'm trying to suppress profile execution on parent and enable it on child during the same build
What is wrong by building the parent?
In fact, in Maven, there are two different concepts (which are generally used at the same time):
The first one is a definition of everything that is common with all the children. You define a parent as a pom-packaged project, and you can install it in your repository.
When you build a child of this parent, Maven2 will retrieve this parent to merge the parent pom with the child pom. You can have a look to the entire pom.xml by running the command mvn help:effective-pom.
In this case, the parent pom will not be built, it will just be retrieved from the repository.
The second case is a project that contains a modules list of sub-projects. The principle is that every command that you run on this project will also be run on all the sub-modules. The order of the modules will be defined by the Reactor, which will look at inter-modules dependencies to find which module must be built before the others. If there are no dependencies, then it will take the list of the modules as they are defined in the parent pom.xml.
In this case, if you run a command on the root project, Maven2 will first built the root project, and then the sub-modules. You cannot skip the creation of the root project.
Edit, thanks to RichSeller comment
A complete explanation of the differences between multi-modules (aggregation project) and inheritance (parent project) can be found in the Maven book, here.