# 2. Dependency Configurations

version 9.0.0

Every dependency declared for a Gradle project applies to a specific scope.

For example, some dependencies should be used for compiling source code whereas others only need to be available at runtime:

build.gradle.kts

    dependencies {
        implementation("com.google.guava:guava:30.0-jre")   // Needed to compile and run the app
        runtimeOnly("org.slf4j:slf4j-simple:2.0.13")        // Only needed at runtime
    }

build.gradle

    dependencies {
        implementation("com.google.guava:guava:30.0-jre")   // Needed to compile and run the app
        runtimeOnly("org.slf4j:slf4j-simple:2.0.13")        // Only needed at runtime
    }

Dependency configurations are a way to define different sets of dependencies for different purposes within a project. They determine how and when dependencies are used in various stages of the build process.

Configurations are a fundamental part of dependency resolution in Gradle.

## Understanding dependency configurations

Gradle represents the scope of a dependency with the help of a Configuration. Every configuration can be identified by a unique name.

Many Gradle plugins add pre-defined configurations to your project.

The Java Library plugin is used to define a project that produces a Java library. The plugin adds many dependency configurations. These configurations represent the various classpaths needed for source code compilation, executing tests, and more:

Configuration Name | Description | Used to:
--- | --- | ---
`api` | Dependencies required for both compilation and runtime, and included in the published API. | Declare Dependencies
`implementation` | Dependencies required for both compilation and runtime. | Declare Dependencies
`compileOnly` | Dependencies needed only for compilation, not included in runtime or publication. | Declare Dependencies
`compileOnlyApi` | Dependencies needed only for compilation, but included in the published API. | Declare Dependencies
`runtimeOnly` | Dependencies needed only at runtime, not included in the compile classpath. | Declare Dependencies
`testImplementation` | Dependencies required for compiling and running tests. | Declare Dependencies
`testCompileOnly` | Dependencies needed only for test compilation. | Declare Dependencies
`testRuntimeOnly` | Dependencies needed only for running tests. | Declare Dependencies

### Dependency declaration Configurations

The dependency declaration configurations (`compileOnly`, `implementation`, `runtimeOnly`) focus on declaring and managing dependencies based on their usage (compile time, runtime, API exposure):

    dependencies {
        implementation("com.google.guava:guava:30.1.1-jre")     // Implementation dependency
        compileOnly("org.projectlombok:lombok:1.18.20")         // Compile-only dependency
        runtimeOnly("mysql:mysql-connector-java:8.0.23")        // Runtime-only dependency
    }

    dependencies {
        implementation("com.google.guava:guava:30.1.1-jre")     // Implementation dependency
        compileOnly("org.projectlombok:lombok:1.18.20")         // Compile-only dependency
        runtimeOnly("mysql:mysql-connector-java:8.0.23")        // Runtime-only dependency
    }

### Other Configurations

There are other types of configurations (such as `runtimeClasspath`, `compileClasspath`, `apiElements`, `runtimeElements`), but they are not used to declare dependencies.

It is also possible to create custom configurations. A custom configuration allows you to define a distinct group of dependencies that can be used for specific purposes, such as toolchains or code generation, separate from the standard configurations (e.g., `implementation`, `testImplementation`):

build.gradle.kts

    val customConfig by configurations.creating

    dependencies {
        customConfig("org.example:example-lib:1.0")
    }

build.gradle

    configurations {
        customConfig
    }

    dependencies {
        customConfig("org.example:example-lib:1.0")
    }

Creating a custom configuration helps manage and isolate dependencies, ensuring they are only included in the relevant classpaths and build processes.

## Viewing configurations

The `dependencies` task provides an overview of the dependencies of your project. To focus on the information about one dependency configuration, provide the optional parameter `--configuration`.

The following example show dependencies in the `implementation` dependency configuration of a Java project:

    $ ./gradlew -q app:dependencies --configuration implementation

    ------------------------------------------------------------
    Project ':app'
    ------------------------------------------------------------

    implementation - Implementation only dependencies for source set 'main'.
    \--- com.google.guava:guava:30.0-jre

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