Groovy & Gradle: JVM Automation and Build Engineering · Lesson

Subprojects & Configurations

Define and configure subprojects, understanding how they interact within a multi-project build.

Subprojects & Configurations is a free Groovy & Gradle: JVM Automation and Build Engineering lesson on CoddyKit — lesson 2 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Groovy & Gradle: JVM Automation and Build Engineering learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.

Welcome to Subprojects!

In large software projects, keeping everything in one giant build file can get messy. This is where subprojects come in handy!

Subprojects allow you to break down a big project into smaller, manageable modules. Think of them as mini-projects living within your main project.

Modularity: Organize code logically.
Reusability: Share common logic across modules.
Faster Builds: Gradle can optimize builds by only working on changed subprojects.

Declaring Subprojects

To tell Gradle about your subprojects, you use the settings.gradle file. This file lives in your root project directory.

You use the include keyword, followed by the path to your subproject's directory. Each subproject usually resides in its own folder.

/* settings.gradle */
rootProject.name = 'my-multi-project'

include 'app'
include 'library'

Subproject Directory Structure

Once declared in settings.gradle, your project structure will typically look like this:

my-multi-project/ (root project)
- settings.gradle
- build.gradle (root build file)
- app/ (subproject 1)
  - build.gradle
  - ... (source code, resources)
- library/ (subproject 2)
  - build.gradle
  - ... (source code, resources)

Each subproject gets its own build.gradle file.

Subproject Build Files

Just like your root project, each subproject has its own build.gradle file. This allows you to define specific configurations, dependencies, and tasks for that particular module.

For example, your app subproject might build a runnable application, while your library subproject might produce a reusable JAR.

/* library/build.gradle */
plugins {
    id 'java'
}

group 'com.coddykit'
version '1.0-SNAPSHOT'

repositories {
    mavenCentral()
}

dependencies {
    testImplementation platform('org.junit:junit-bom:5.9.1')
    testImplementation 'org.junit.jupiter:junit-jupiter'
}

Defining a Subproject Task

You can define tasks within a subproject's build.gradle file. These tasks are then specific to that subproject.

Let's add a simple task to our library subproject that prints a message.

/* library/build.gradle */
plugins {
    id 'java'
}

group 'com.coddykit'
version '1.0-SNAPSHOT'

repositories {
    mavenCentral()
}

task helloLibrary {
    doLast {
        println "Hello from the Library subproject!"
    }
}

Executing Subproject Tasks

To run a task belonging to a specific subproject from the root directory, you use a colon : to separate the subproject name and the task name.

For example, to run the helloLibrary task from our library subproject:

public class Main {
  public static void main(String[] args) {
    System.out.println("To run the task: gradle :library:helloLibrary");
    System.out.println("Output will be: Hello from the Library subproject!");
  }
}

Common Configuration: allprojects

Sometimes, you want to apply the same configuration to all projects in your multi-project build (the root project and all its subprojects).

You can do this using the allprojects { ... } block in your root build.gradle file.

/* build.gradle (root) */

allprojects {
    group 'com.coddykit.common'
    version '1.0.0'

    repositories {
        mavenCentral()
    }
}

Targeting Specific Subprojects

While allprojects is great for common settings, you often need to configure individual subprojects from the root build file.

You can use the project(':subprojectName') { ... } block to apply configuration specifically to one subproject.

/* build.gradle (root) */

project(':app') {
    apply plugin: 'application'
    mainClassName = 'com.coddykit.app.MainApp'
}

project(':library') {
    apply plugin: 'java-library'
}

Sharing Properties

You can also share properties or variables from your root project to all subprojects. This is useful for things like consistent version numbers or build flags.

Use the ext block (for "extra properties") in the root build.gradle and access it with rootProject.ext.propertyName in subprojects.

/* build.gradle (root) */
ext {
    groovyVersion = '3.0.9'
    springBootVersion = '2.7.5'
}

allprojects {
    // Access properties in subprojects
    println "Groovy Version: ${rootProject.ext.groovyVersion}"
}

Multi-Select Check

Which of the following statements about Gradle subprojects and their configuration are TRUE?

Subprojects Recap

Great job! You've learned the basics of setting up and configuring Gradle subprojects.

Subprojects help organize large builds.
They are declared in settings.gradle using include.
Each subproject has its own build.gradle.
You can configure all projects using allprojects { ... } or specific ones using project(':name') { ... }.
Tasks are run with the :subproject:task syntax.

Next, we'll explore how subprojects can depend on each other!

Frequently asked questions

Is the “Subprojects & Configurations” lesson free?

Yes — the full text of “Subprojects & Configurations” is free to read here on the web, and the Groovy & Gradle: JVM Automation and Build Engineering course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Groovy & Gradle: JVM Automation and Build Engineering course, upgrade to CoddyKit PRO.

What will I learn in “Subprojects & Configurations”?

Define and configure subprojects, understanding how they interact within a multi-project build. You practise Groovy & Gradle: JVM Automation and Build Engineering with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.

Do I need any experience to start Groovy & Gradle: JVM Automation and Build Engineering?

No prior experience is required. Groovy & Gradle: JVM Automation and Build Engineering on CoddyKit is structured for beginners through advanced learners; this is — lesson 2 of 4, so you can start here or from the beginning and move at your own pace.

How long does the “Subprojects & Configurations” lesson take?

Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.

Can I write and run code in this Groovy & Gradle: JVM Automation and Build Engineering lesson?

Yes. Every Groovy & Gradle: JVM Automation and Build Engineering lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.

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