When the same library is declared multiple times or when two different libraries provide the same functionality, a conflict can occur during dependency resolution.

Understanding types of conflicts

During dependency resolution, Gradle handles two types of conflicts:

  1. Version conflicts: That is when two or more dependencies require a given module but with different versions.

  2. Capability conflicts: That is when the dependency graph contains multiple artifacts that provide the same functionality.

Resolving version conflicts

A version conflict occurs when a component declares two dependencies that:

  • Depend on the same module, let’s say com.google.guava:guava

  • But on different versions, let’s say 20.0 and 25.1-android

    • Our project itself depends on com.google.guava:guava:20.0

    • Our project also depends on com.google.inject:guice:4.2.2 which itself depends on com.google.guava:guava:25.1-android

Gradle will consider all requested versions, wherever they appear in the dependency graph. By default, it will select the highest one out of these versions.

Resolving capability conflicts

Gradle uses attributes and capabilities to identify which artifacts a component provides. A capability conflict occurs whenever two or more variants of a component in dependency graph declare the same capability.

Gradle will generally fail the build and report the conflict.

You can resolve conflicts manually by specifying which capability to use in the resolutionStrategy block:

configurations.all {
    resolutionStrategy.capabilitiesResolution.withCapability("com.example.logging") {
        selectHighestVersion()
    }
}

Understanding dependency constraints

In order to help Gradle resolve issue with dependencies, a number of solutions are provided.

For example, the dependencies block provides a constraints block which can be used to help Gradle pick a specific version of a dependency:

dependencies {
    constraints {
        implementation("org.apache.commons:commons-lang3:3.12.0")
    }
}

Next Step: Learn about Dependency Resolution >>