Difference Between implementation and compile in Gradle

1. Introduction

Gradle 8 provides three main dependency configurations for configuring dependencies in software projects: compileOnly, implementation, and api. While these dependency configurations may have some overlap, they’ve different implications and usage. Therefore, it’s important to understand the differences between them to use them effectively.

In this tutorial, we’ll discuss the difference between these three dependency management configurations in Gradle 8. Further, we’ll provide best practices for effective dependency management.

2. What Is compileOnly in Gradle Dependency Management?

When we configure a dependency as compileOnly, Gradle only adds it to the compile-time classpath. Gradle doesn’t add it to the build output. Accordingly,  Gradle makes the dependency available during compilation, but not at runtime when the program is executed. The compileOnly dependency configuration helps reduce the size of the build output; and as a result, reduces the build time and memory use.

Let’s consider a simple Gradle script:

dependencies {
    compileOnly 'org.hibernate.orm:hibernate-core:6.6.3.Final'
    testCompileOnly 'org.junit.jupiter:junit-jupiter:5.11.4'
}

In this example, we’re including a dependency on the hibernate-core library with version 6.6.3.Final from the org.hibernate.orm group using the compileOnly configuration. This Gradle includes this dependency in only the compile-time classpath.

We’re also including a dependency on the JUnit testing framework with version 5.11.4 using the testCompileOnly configuration. Gradle includes this dependency only in the test compilation classpath, which is used when compiling tests. Gradle doesn’t include this dependency in the test runtime classpath, which is used when running tests.

3. What Is implementation in Gradle Dependency Management?

When we configure a dependency as implementation, Gradle adds it to both the compile-time and runtime classpaths. This means Gradle makes the dependency available during compile-time and also at runtime when the program is executed. Gradle packages the dependency to the build output. However, the implementation dependency configuration increases the size of the build output, which in turn increases the build time and accompanying memory use, as compared to the compile-only configuration.

Let’s consider a simple Gradle script:

dependencies {
    implementation 'org.hibernate.orm:hibernate-core:6.6.3.Final'
    testImplementation 'org.junit.jupiter:junit-jupiter:5.11.4'
}

In this example, we’re including a dependency on the hibernate-core library with version 6.6.3.Final from the org.hibernate.orm group using the implementation keyword. Gradle includes this dependency in the compile-time classpath and the runtime classpath.

We’re also including a dependency on the JUnit testing framework with version 5.11.4 using the testImplementation keyword. Gradle includes this dependency in both the test compile-time classpath and the test runtime classpath, making it available for compiling and running tests.

4. Difference Between compileOnly and implementation

The main difference between compileOnly and implementation in Gradle is that compileOnly includes the dependency in only the compile-time classpath, whereas implementation includes the dependency in both the compile-time and runtime classpaths. This means when we configure a dependency as implementation, Gradle makes it available during runtime, whereas when we configure a dependency as compileOnly, Gradle doesn’t make it available during runtime.

Additionally, compileOnly provides better separation between the compile-time and runtime classpaths, making it easier to manage dependencies and avoid version conflicts. Choosing the right dependency configuration can have implications for project performance, build times, and compatibility with other dependencies.

5. What Is api in Gradle Dependency Management?

When we configure a dependency as api, Gradle adds it to the compile-time and runtime classpaths and includes it in the published API. This means Gradle makes the dependency available when the program compiles, when the program runs, and when dependent module programs compile. Gradle packages the dependency to the build output. Furthermore, Gradle includes the dependency in the published API. The api dependency configuration increases the build time and accompanying memory use, as compared to the implementation configuration.

Let’s consider a simple Gradle script:

dependencies {
    api 'org.hibernate.orm:hibernate-core:6.6.3.Final'
    testRuntimeOnly 'org.junit.jupiter:junit-jupiter:5.11.4'
}

In this example, we’re including a dependency on the hibernate-core library with version 6.6.3.Final from the org.hibernate.orm group using the api keyword. This dependency will included in the compile-time classpath and the runtime classpath. Furthermore, Gradle includes the dependency in the published API.

We’re also including a dependency on the JUnit testing framework with version 5.11.4 using the testRuntimeOnly keyword. Gradle includes this dependency only in the test runtime classpath and not in the published API.

6. Difference Between implementation and api

The main difference between implementation and api in Gradle is that implementation doesn’t transitively export the dependency to other modules that depend on this module. In contrast, api transitively exports the dependency to other modules. This means that dependencies configured with api are available to other modules, which depend on this module, both at runtime and compile time. However, dependencies configured with implementation are available to other modules, which depend on this module only at runtime.

Therefore, we should use the api configuration with caution because it increases the build time significantly over the implementation configuration. As an example, if an api dependency changes its external API, Gradle recompiles all modules that have access to that dependency, even at compile time. In contrast, if an implementation dependency changes its external API, Gradle doesn’t recompile all modules even when the software in the modules is not running because the dependent modules don’t have access to that dependency at compile time.

Gradle provides two other dependency configurations: compileOnlyApi and runtimeOnly. When we configure a dependency as compileOnlyApi, Gradle uses it for compilation only, just like compileOnly. Additionally, Gradle includes it in the published API. When we configure a dependency as runtimeOnly, Gradle includes it in the build output for runtime, although it doesn’t use it at compile time.

7. Best Practices for Gradle Dependency Management

To ensure effective dependency management in Gradle, we should consider a few best practices:

• Use the implementation configuration by default
• Use the compileOnly configuration when you don’t want to package the dependency in the build output. An example use case is a software library that only includes compile-time annotations, which are typically used to generate code but are not needed at runtime
• Avoid using the api configuration, as it can lead to longer build times and increased memory usage
• Use specific versions of dependencies instead of dynamic versioning to ensure consistent behavior across builds
• Keep the dependency graph as small as possible to reduce complexity and improve build times
• Regularly check for updates to dependencies and update them as necessary to ensure that the project uses the latest and most secure versions
• Use dependency locking to ensure that builds are reproducible and consistent across different machines and environments

8. Conclusion

In this article, we discussed the difference between compileOnly, implementation, and api dependency configurations in Gradle. Further, we discussed how they affect the scope of dependencies in a project. We provided examples and best practices for Gradle Dependency Management.

By following these practices, we can ensure that our builds are reliable, efficient, and easy to maintain.