Maven versus Gradle: what a newcomer needs to build someone else's JVM project

What it is

Maven: pom.xml declares coordinates (groupId, artifactId, version), dependencies with scopes, and plugins. The lifecycle guide states there are three built-in lifecycles (default, clean, site); the default lifecycle runs its phases in a fixed order and invoking one phase runs all earlier ones, so mvn verify validates, compiles, tests, packages and runs integration checks. Plugin goals bind to phases. Dependency scopes (compile by default, provided, runtime, test, and import for BOMs) decide which classpaths a dependency reaches. The dependency guide states that conflicting versions are mediated by the "nearest definition" in the tree, the first declaration winning at equal depth, and that dependencyManagement pins versions for transitive dependencies.

Gradle: the basics guide describes a build in terms of projects and tasks configured by build scripts (build.gradle in Groovy or build.gradle.kts in Kotlin) plus a settings.gradle(.kts) file, with plugins adding tasks and conventions. Dependencies are declared in configurations such as implementation and testImplementation. When two paths request different versions of a module, the conflict-resolution chapter states that Gradle by default selects the highest of the requested versions. Gradle offers optional dependency locking; Maven has no built-in lock file, so repeatability comes from exact versions and BOM imports.

Why it matters

An engineer used to npm, cargo or pip must first find which tool and which version the repository expects. Both ecosystems answer with a wrapper committed to the repository: ./gradlew, which the Gradle documentation calls the recommended way to run a build, and Maven's optional ./mvnw. Running a globally installed tool of another version is the most common first mistake, followed by assuming the other tool's conflict rule.

How to apply

• Use the wrapper: ./gradlew build or ./mvnw verify; fall back to a global install only when no wrapper exists.
• Maven: read pom.xml top to bottom (parent, properties, dependencyManagement, dependencies, build plugins); mvn dependency:tree shows what mediation chose.
• Gradle: read settings.gradle(.kts) for the project list, then the build script; ./gradlew tasks and ./gradlew dependencies --configuration runtimeClasspath explain the build.
• Skip tests visibly and only for local iteration: -DskipTests (Maven), -x test (Gradle).
• Multi-module builds: Maven's reactor orders modules by their dependencies from the root POM; Gradle subprojects are listed in the settings file.

Pitfalls

Maven's nearest-definition rule can select an older version than a transitive dependency needs; Gradle's highest-version rule can pull in a newer one than any module was tested with. Gradle build scripts are code and can do anything. mvn install writes to the local repository and can mask a missing publication. Both cache downloaded artifacts, so CI caches need a key derived from the build files.