Multi-project build - project dependencies and build order

I need to migrate a multi-project build from maven to gradle and maintain the way inter-project dependencies and build order work. I’d like to use the maven plugin in gradle and continue to publish artifacts to both local and remote maven repositories.

The multi-project structure is like so:

In maven Project-A2 has a dependency on Project-A1. If I run mvn install_ from the Project-A2 directory it will only build/install that project and pull it’s dependency on Project-A1 from the local/remote maven repository. If I run mvn install from Project-A it will build/install both Project-A1 and A2 and calculate the build order based on the above mentioned dependency. How can this same behavior be achieved in gradle?

Additionally, Project-B2 has a dependency on Project-A2. If I run mvn install from the Project-B2 or Project-B directories this dependency should be pulled from the local/remote maven repository. If I run mvn install from the root directory it should calculate the build order such that Project-A1 builds, _Project-A2 builds, and then Project-B2 builds.

Could you explain why you want to mimic this behavior in Gradle? Why not build Project-A1? Gradle has excellent support for incremental builds, so this will be fast and correct.

The main concern is build time. If it were simply one small project depending on another it’s not really an issue. I’m working with a number of cases where a relatively small project depends on one or more larger projects. If the project I want to build takes 5 minutes but it’s dependencies take 30 minutes it’s not ideal to build both and end up with a 35 minute build time.

The incremental build support is great and after building everything once it looks like it should address this need. However I do need to consider the case where someone checks out the source fresh and only wants to build a small piece. They’re not going to want to wait for multiple dependencies to build when they could be pulled in from a repository.

Are these real numbers or hypothetical? Note that the upstream dependencies only need to create their outputs. They won’t run tests or other time-consuming tasks.

If your projects actually take that long just to compile, then you might be interested in either:

  • breaking your big build into smaller builds (inside the same repo) using Composite Builds
  • our upcoming distributed cache support

Those numbers are hypothetical but our total build time does reach between 2-3 hours without test and there are cases that exist similar to that example.

I’ll take a look at composite builds and the distributed cache support. It sounds like a little restructuring of the projects/process to better fit gradle is the direction to go. Thanks for the suggestions!

Maybe I misunderstood your description: Is the 2-3h build time with Maven or Gradle? Gradle is much faster than Maven, so I’d suggest first going with the straightforward multi-project approach and only optimizing if you actually hit a problem.

2-3 hours in maven. I don’t have an estimate for gradle yet due to trying to work out the best approach ahead of converting the entire maven build to gradle. I’ve only been working with a small piece of our source with gradle.

If the best way to tackle this is to setup the multi-project and then look into composite builds, distributed cache support etc. then that’s what I’ll do. I assumed that we would see similar build time/dependency related problems in gradle as we do in maven but if that’s not the case that’s great. Thanks!