Buildish Mammoth Cache for Gradle and Maven

Buildish Mammoth Cache for Gradle and Maven is a pair of CI actions that cache the build tool’s local artifact store across workflow runs:

• Gradle — caches GRADLE_USER_HOME and provisions Gradle wrapper JARs securely before the build starts.
• Maven — caches the Maven local repository (~/.m2 by default).

Both actions share the same two-phase prepare/finalize lifecycle and support single-job and distributed multi-job topologies.

Single-job mode

In the most common setup, the action wraps a single build job: it restores the newest compatible immutable generation before the build and publishes a new complete generation after a material change. This avoids re-downloading dependencies on every run without creating duplicate entries for unchanged runs.

Distributed multi-job mode

When a workflow runs multiple build jobs in parallel — for example, one job per subproject or one job per test suite — independent full-cache generations diverge. Restoring only the newest generation then loses the dependency downloads that exist solely in the other workers’ generations.

This action solves that with a delta exchange model:

• Each worker job computes only the difference between what was in the cache when it started and what is in the cache after the build. It uploads that delta as a workflow artifact.
• A dedicated aggregator job, which runs after all workers complete, downloads every delta, merges them, and saves the merged result as the new base cache entry.

The result: every parallel job’s dependency downloads are captured in one merged generation.

graph LR
    BC["Base cache\n(previous run)"] --> W1 & W2 & W3
    W1["Worker A\nbuild + delta"] -- "Δ artifact A" --> AGG
    W2["Worker B\nbuild + delta"] -- "Δ artifact B" --> AGG
    W3["Worker C\nbuild + delta"] -- "Δ artifact C" --> AGG
    AGG["Aggregator\nmerge + save"] --> BC2["Base cache\n(this run)"]