モノレポのプロジェクト構成

Welcome to the world of monorepos! A monorepo is a single version-controlled code repository that holds multiple distinct projects. Think of it as a super-repository for all your related applications and libraries.

This is different from a polyrepo, where each project lives in its own separate repository. Monorepos are becoming increasingly popular, especially for large organizations.

Gradle is an excellent build tool for managing monorepos. Its powerful multi-project capabilities are specifically designed to handle complex relationships between many projects within a single build.

Using Gradle, you can define how all your projects are structured, built, and tested from one central place, making development smoother and more consistent.

The heart of a Gradle multi-project build (and thus a monorepo) is the settings.gradle file. This file sits at the root of your monorepo and tells Gradle which subprojects are part of the overall build.

You use the include keyword to add subprojects. Each subproject usually corresponds to a subdirectory.

Each project within your monorepo is called a subproject. A subproject is typically represented by a subdirectory within your main monorepo folder.

Just like a standalone project, each subproject has its own build.gradle file, where you define its specific dependencies, tasks, and configurations.

• Folder Structure: my-monorepo/app/, my-monorepo/library/
• Build File: app/build.gradle, library/build.gradle

The top-level directory of your monorepo is known as the root project. It usually contains the settings.gradle file and often a build.gradle file of its own.

The root build.gradle is a perfect place to define settings that apply to all subprojects, ensuring consistency across your entire codebase without repeating yourself.

One major benefit of Gradle monorepos is sharing common build logic. In your root build.gradle, you can use allprojects {} or subprojects {} blocks to apply configurations globally.

This is great for defining common repositories, applying standard plugins (like java or groovy), or setting a consistent version for all components.

Let's visualize a basic monorepo structure. You'll typically have your root Gradle files and then separate directories for each subproject, each with its own build.gradle.

• my-monorepo/
• ├── settings.gradle
• ├── build.gradle (root build script)
• ├── app/ (subproject)
• │ └── build.gradle
• │ └── src/main/groovy/App.groovy
• └── library/ (subproject)
• └── build.gradle
• └── src/main/groovy/Library.groovy

Each subproject contains its own specific code. Here's a very simple Groovy class with a main method. Imagine this file lives inside your app subproject (e.g., at app/src/main/groovy/App.groovy).

While Gradle manages the build, the core logic is still written in your chosen language, like Groovy!

To make the previous App.groovy runnable via Gradle, your subproject's build.gradle (e.g., app/build.gradle) would configure the application plugin and specify the mainClassName.

Then, from the root of your monorepo, you could simply run gradle :app:run to execute it!

Monorepos offer several advantages, but also come with considerations:

• Advantages:
• Shared Code: Easier to share code and logic between projects.
• Atomic Changes: Refactoring across projects is simpler and safer.
• Consistent Builds: Standardized build process across all components.
• Considerations:
• Repo Size: Can grow very large over time.
• Build Times: Can become slower if not optimized (e.g., using Gradle's build cache).
• Tooling: IDEs and other tools might need specific configurations.

Great job! You've learned the fundamentals of setting up a monorepo with Gradle.

You now understand the roles of settings.gradle and the root build.gradle, and how to structure your subprojects. In the next lessons, we'll dive deeper into configuring individual subprojects and managing dependencies between them.