maven deploy changed artifacts only - maven-2

Question

I'm using maven 2.2 with nexus 1.4.0
Let's say I have a pom-structure like this (with corresponding versions)
parentproj, v1.0.1
- childproj1, v1.0.2
- childproj2, v1.0.7
childproj1 and childproj2 represent different parts of the application (e g gui and backend) and I want to be able to keep their versions separate so that I can release a new version of the backend without having to release a new version of the gui.
Now, to deploy this structure to Nexus it would be convenient to go to parentproj and say
mvn deploy -DperformRelease=true
which would deploy all artifacts to the Nexus realease repository. This works fine the first time I deploy it, but the second time I run into problems: let's say that I made an update to childproj1 so that we now have the following versions:
parentproj, v1.0.1
- childproj1, v1.0.3
- childproj2, v1.0.7
In this situation Nexus will not let me do mvn deploy from parentproj, since it already has a copy of childproj2 in the 1.0.7 version. Nexus will say "Resource, illegal request:Repository with ID='releases' does not allow updating artifacts." This is fine, I don't want to update existing versions by mistake.
But I guess that what I would like to do is to be able to tell maven something like "deploy only those artifacts that have versions that are not already present in the release repository".
Is there a way to do this, or would I have to deploy each project by itself?

Answer 1

In my experience, it has been easier to deploy everything, and often use the same version number for all the components. For example, if my team is working on version 1.0.7, all the submodules have the version number of 1.0.7-SNAPSHOT, until we release, even if no code has changed in certain modules. Then when we deploy, we would deploy the whole application. I think it has several advantages over a piecemeal deployment. First, if you every have to rollback to the last stable version, you just have to rollback to 1.0.6 for all modules--you don't have to remember that the backend was 1.0.3 while the GUI was 1.0.6. Second, it ensures that all the components are compiled correctly against each other and have been tested as a logical group.
Sorry, I know this isn't a specific answer to your question, but, at least in my team's case, it was useful to think slightly differently

Answer 2

First of all, I think you should distinguish between parent project and aggregation project. Parent projects should be used for those settings that are common to several projects, e.g. dependencies' versions; aggregation projects should be used in order to build at the same time a group of projects, e.g. a set of jars and the war that includes them.
The two kind of projects are best kept separated. The parent project usually does not change very often and when it does it is usually best to release new versions of all the projects that depend from it; the aggregation project's only purpose is to drive the build of a bunch of projects, so its release number should probably change whenever one of the projects it contains needs to be released.
Once you've separated parent from aggregator you're in a better position to choose whether to follow John Paulett's advice and keep everything at the same version number or to try and change each project's version number only when you actually need to release it. The first option is simpler and less error prone, but causes you to release new version of libraries that haven't changed. This might not be acceptable if, for instance, you need to ship patches rather than full releases. The second option is more complicated and error prone, but causes your release numbers to match the evolution of your software. The Maven release plugin and the Jenkins continuous integration tool may be of help there, I think you should check them out. Also, see if you can upgrade Maven to at least version 2.2.1 and Nexus to a more recent version.

Answer 3

I would suggest you Artifact Exists Maven Plugin (https://github.com/chonton/exists-maven-plugin). This wonderful thing requires only to be mentioned on the parent.pom, and will automatically skip the install and deploy phase for all release artifacts, that already exists in repository (Nexus or Artifactory). And still deploy the Snapshots (this is configurable).
Example:
<plugin>
<groupId>org.honton.chas</groupId>
<artifactId>exists-maven-plugin</artifactId>
<version>0.0.6</version>
<executions>
<execution>
<goals>
<goal>remote</goal>
</goals>
</execution>
</executions>
</plugin>
</plugins>

Answer 4

I would suggest that if you plan to maintain, build, and deploy the modules independently, you should consider setting up separate CI and mvn deploy jobs for each. Having independent mvn deploy jobs will give you the behavior you are looking for out of the box. This means not using the aggregator pom (parentprj) to attempt building and deploying these modules.
If you want to do everything from the aggregator pom, like build and deploy, then I would suggest following John's answer and keeping all the version number in sync.
It just depends on how your team wants to look at the code base. If you want to keep things in a true modular fashion, you should be using your maven modules like building blocks, treating them differently, until you are ready to put the whole app together. If your app is more monolithic in nature, treat it as so and keep things in sync. This doesn't mean you still can't break out separate maven modules for maintaining code-base modularity, just recognize they don't have any value outside the context of your larger app.
A good way of making this decision is asking yourself "Will any other projects/apps need to reference this module as a dependency?". If so, it is best practice to build, version, and deploy it independently. If not, I don't see any pitfalls to making the versions match up.

Answer 5

Clearly this need is not addressed by maven, neither by Nexus or archiva.
For now it can only be addressed by additional tricks setup by the build manager like the ones suggested in previous posts.
In an ideal world
the pom would include
. both the release version and the snapshot version of the module
. a definition of the files which, if changed, justify the use of the snapshot version
. the source control management system reference of the released module
dependent modules poms would add in the appropriate dependency section the release version info next to the snapshot version info so that it links to the snapshot library if present in the repo and the release library otherwise
the maven reactor would have an option to read both the dependency hierarchy and the file changes info (scm diff) to know whether a given module is to be used in its release or snapshot version.
the release plugin would by default skip the releasing of the modules whitch still can be used with their release version based on the file changes and the dependency info.