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Modularization in Gradle Projects with Kotlin

 ·  ☕ 4 min read  ·  ✍️ Ignacio Carrión

Modularization in Gradle Projects with Kotlin: A Comprehensive Guide

Introduction

As projects grow in complexity, maintaining a monolithic codebase becomes challenging. Modularization is a software design technique that breaks down an application into smaller, independent modules, making the project more scalable, maintainable, and efficient.

In this guide, we’ll explore why modularization is essential, different types of modules, and best practices for setting up a modular Gradle project using Kotlin.


Why Modularization?

Before implementing modularization, it’s important to understand its key benefits:

  • Faster Build Times – Gradle compiles independent modules in parallel, reducing build times.
  • Scalability – Easier to manage and extend large projects.
  • Encapsulation – Each module has a well-defined responsibility, improving separation of concerns.
  • Team Collaboration – Teams can work independently on different modules, reducing merge conflicts.
  • Reusability – Common functionality can be extracted into reusable modules.

Example Scenario

Imagine an Android app where all features and dependencies reside in a single app module. This setup leads to long build times, tightly coupled code, and difficulties in testing. With modularization, features and shared functionalities can be isolated into separate modules, improving efficiency.


Types of Modules in a Gradle Project

Feature Modules

Contain independent features of the app, such as:

  • feature-auth (Authentication screens)
  • feature-dashboard (Home screen, user data)
  • Can be dynamically loaded using Dynamic Feature Modules in Android.

Library Modules

Reusable components shared across the app, such as:

  • ui-components (Custom buttons, toolbars)
  • networking (API calls, Retrofit setup)
  • analytics (Logging, Firebase events)

Core Modules

Contains shared utilities, such as:

  • core-utils (Common utilities, extensions)

Gradle Setup for Modularization

After defining module types, configuring dependencies correctly is crucial.

Using api, implementation, and compileOnly

  • implementation – Dependency is only visible within the module.
  • api – Dependency is exposed to other modules.
  • compileOnly – Used for compile-time dependencies.

Example:

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// In feature-auth/build.gradle.kts
dependencies {
    implementation(project(":core-utils")) // Only visible in this module
    compileOnly("androidx.annotation:annotation:1.3.0")
}

Dependency Management in Gradle

Managing dependencies across multiple modules can be simplified using Version Catalogs, which is the recommended approach in modern Gradle projects.

Gradle’s Version Catalogs allow defining dependencies in a .toml file, ensuring consistency and easy updates across modules. This method is now the preferred way to manage dependencies in Gradle.

Step 1: Define Dependencies in libs.versions.toml

Create or update the gradle/libs.versions.toml file:

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[versions]
retrofit = "2.9.0"
coroutines = "1.6.4"

[libraries]
retrofit = { module = "com.squareup.retrofit2:retrofit", version.ref = "retrofit" }
coroutines = { module = "org.jetbrains.kotlinx:kotlinx-coroutines-core", version.ref = "coroutines" }

Step 2: Use Version Catalog in build.gradle.kts

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dependencies {
    implementation(libs.retrofit)
    implementation(libs.coroutines)
}

This approach provides:

  • Centralized Dependency Management – All versions are stored in one place.
  • Safer Updates – Easy bulk updates and compatibility checks.
  • Better Maintainability – Reduces duplication across multiple build.gradle.kts files.

If your project is still using buildSrc, consider migrating to Version Catalogs, as Gradle actively recommends this approach.


Example Modular Architecture in Kotlin

Folder Structure of a Modular Project

my-app/
│── app/                 # Main application module
│── core/
│   ├── core-utils/       # Common utilities
│── features/
│   ├── feature-auth/     # Login, signup
│   ├── feature-dashboard/ # Dashboard, home screen
│── libraries/
│   ├── ui-components/    # Shared UI elements
│   ├── networking/       # Retrofit setup, API client

Dependency Flow

  • feature-auth → depends on core-utils and networking
  • app → depends on all feature modules (feature-auth, feature-dashboard)

Best Practices for Modularization

Avoid Cyclic Dependencies

  • Feature modules should not depend on each other directly.
  • Use event-based communication (e.g., LiveData, Flow).

Use Dependency Injection (DI)

  • Libraries like Koin help manage dependencies.

Optimize Gradle Build Speed

  • Enable Gradle’s configuration cache:
org.gradle.parallel=true
org.gradle.caching=true

Conclusion

By implementing modularization in Gradle projects, you achieve:

✔️ Faster build times
✔️ Better maintainability
✔️ Scalability for large teams
✔️ Reusable components

Would you like to explore a sample Kotlin project showcasing modularization? 🚀

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Ignacio Carrión
WRITTEN BY
Ignacio Carrión
Android Developer