compileonly

compileOnly is a dependency configuration in Gradle used to declare libraries that are needed to compile the source code but should not be included in the runtime classpath of the produced artifact. Dependencies added with compileOnly are available on the compile classpath during compilation but are not packaged into the artifact and are not intended to be available to users of the library at runtime.

Typical use cases include APIs provided by the deployment environment (for example, the Servlet API when building a web application that runs in a container) or libraries that are only needed for development-time checks and code generation. Annotation processors can also be configured separately (for example, via annotationProcessor), while compileOnly ensures the processor’s API is visible at compile time without being bundled at runtime.

Usage examples in Gradle:

- Groovy DSL: dependencies { compileOnly 'org.projectlombok:lombok:1.18.20' }

- Kotlin DSL: dependencies { compileOnly("org.projectlombok:lombok:1.18.20") }

Notes:

- In the usual Gradle Java Library setup, compileOnly works alongside implementation, api, and runtimeOnly. Implementation and api bring transitive dependencies into both compile and runtime, while runtimeOnly adds dependencies only to the runtime classpath.

- CompileOnly is not suitable for dependencies that are required at runtime by the produced artifact. If a consumer module needs such a dependency at runtime, it must be provided by that consumer.

Overall, compileOnly helps keep runtime footprints small and avoids packaging environment-provided or non-runtime dependencies, while still enabling compile-time access to their symbols.