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[[two-dependency-configurations]]
= 2. Dependency Configurations

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:

====
[.multi-language-sample]
=====
[source, kotlin]
.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
}
----
=====
[.multi-language-sample]
=====
[source, groovy]
.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.

[[sub:what-are-dependency-configurations]]
== Understanding dependency configurations

Gradle represents the scope of a dependency with the help of a link:{groovyDslPath}/org.gradle.api.artifacts.Configuration.html[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:

[cols="~,~,~"]
|===
|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

|===

[[sub:dependency-declaration-configurations]]
=== 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):

====
[.multi-language-sample]
=====
[source, kotlin]
----
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
}
----
=====
[.multi-language-sample]
=====
[source,groovy]
----
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
}
----
=====
====

[[sub:other-configurations]]
=== 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`):

====
[.multi-language-sample]
=====
[source, kotlin]
.build.gradle.kts
----
val customConfig by configurations.creating

dependencies {
    customConfig("org.example:example-lib:1.0")
}
----
=====
[.multi-language-sample]
=====
[source, groovy]
.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.

[[sub:view-configurations]]
== 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:

[source,text]
----
$ ./gradlew -q app:dependencies --configuration implementation

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

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

[.text-right]
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