How to resolve dependencies between modules within multi-module project?

Maven has the concept of a "reactor" where artifacts that have been built in a single run (e.g. maven package) are available for dependency resolution during the build. For example, if your dependency graph yields the build order moduleA moduleB moduleC, and you do mvn package, Maven will build moduleA, package its artifact and add it to the reactor, then build moduleB, package it and add it to the reactor, then the same for moduleC. This means moduleB has access to moduleA's artifact for dependency resolution, and moduleC has access to moduleA and moduleB. This only works if artifacts are actually built, i.e. when you run the package goal.

The problem is that when you don't run the package goal because you're not interested in the artifacts (as for your dependency:go-offline example), artifacts for modules that have been processed don't get built and thus not added to the reactor. I find this annoying as well; I think Maven should look at the POM files in its list of modules to build and look there as well; but it doesn't.

In short, the solution to your problem is to do mvn package dependency:go-offline . This will not install artifacts in your local repository (which I believe is very bad practice) but it will put them in the reactor for the duration of the build, meaning that Maven will be able to resolve dependencies from your moduleB to the moduleA that has already been built. The downside is every module will be tested and packaged, which is a lot of work when all you wanted is to do dependency:go-offline.

Either way, hope this helps.

You explained why it doesn't work so you understand the issues. The problem for you is that it stops when it can't find A.jar but that will only happen when you get to building B. So there is a sort of, sometimes useful strategy.

You have to mess with A by itself. Just build A. Use your plan of loading dependencies and then building it.

Once it builds, you can move on to doing the same thing with B and then C. Step by step.

One thing to remember here is that its sometimes ok to build B with an old snapshot of A in the local repo. You only need the new snapshot of A build in the repo if there are signature changes or new stuff required by B.

There are some discussions here too: Maven Modules + Building a Single Specific Module

One final not that usually these sort of questions come up when people have builds that take too long. There are several ways to make builds go faster:

1. Get faster hardware. The build computer, the disk storage or the network speed are typical components that are cheaper to upgrade than waste the time taken in slow builds.
2. Make the build go faster by not building stuff that doesn't need rebuilding. (For example, I had a build that rebuilt all the generated code every time. I added some stuff into the build that kept it from doing that except when dependencies to the generated code changed.)
3. Speed up the tests. Sometimes this means breaking the tests into two parts. Part 1 is fast tests and part 2 is slow tests. Run the fast tests on every build and the slow tests before any checkin of code or release of artifacts.
4. Break a multi-module build into 2 or more separate builds and use human intelligence to decide when to rebuild things. This works well when some jars are stable and don't change much any more.
5. Fill in your own method to make the build go faster.

I have created a JIRA ticket with a sample project here:

https://issues.apache.org/jira/browse/MDEP-516

Please vote for it.

This has been finally been resolved with Maven Dependency Plugin version 3.1.2.

You can make sure it's used by pinning the version in your pom.xml:

<build>
    <pluginManagement>
        <plugins>
            <plugin>
                <artifactId>maven-dependency-plugin</artifactId>
                <version>3.1.2</version>
            </plugin>
       </plugins>
    </pluginManagement>
</build>