How To Create a Spring Boot Multi-Module Application

When all the features are crammed into one module, creating a large-scale Spring Boot application can get complicated. Code can be better maintained, reused, and built more efficiently by breaking it up into smaller, more manageable modules with the use of a multi-module Maven or Gradle project. We’ll go over how to establish a Spring Boot multi-module application in this article, along with developer community-recommended best practices and optimizations.

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Why Use a Multi-Module Application?

1. Better Code Organization – Separate concerns (e.g., API, service, repository layers).
2. Reusability – Share common dependencies and configurations across modules.
3. Faster Builds – Only rebuild modified modules, reducing compilation time.
4. Independent Deployment – Some modules (like libraries) can be reused in other projects.

Prerequisites – Spring Boot Multi-Module Application

• Java 17+ (Recommended for Spring Boot 3.x)
• Maven or Gradle (We’ll use Maven in this guide)
• Spring Boot 3.x
• IDE (IntelliJ IDEA, VS Code, or Eclipse)

Step 1: Create a Parent Project

The parent project acts as a container for all modules and manages common dependencies.

Using Spring Initializr

1. Go to https://start.spring.io.
2. Select:
   • Project: Maven
   • Language: Java
   • Packaging: Jar (for modules, we use pom in parent)
3. Click Generate, then extract the project.

Convert to Parent POM

Open pom.xml and modify it:

<project>  
    <modelVersion>4.0.0</modelVersion>  
    <parent>  
        <groupId>org.springframework.boot</groupId>  
        <artifactId>spring-boot-starter-parent</artifactId>  
        <version>3.5.4</version> <!-- Use latest stable version -->  
    </parent>  

    <groupId>com.example</groupId>  
    <artifactId>multi-module-app</artifactId>  
    <version>1.0.0</version>  
    <packaging>pom</packaging> <!-- Parent is of type POM -->  

    <modules>  
        <!-- Child modules will be added here -->  
    </modules>  

    <properties>  
        <java.version>17</java.version>  
    </properties>  
</project>  

Step 2: Create Child Modules

Each module serves a specific purpose (e.g., api, service, repository).

Option 1: Using Command Line (Maven)

Run these commands inside the parent directory:

mvn archetype:generate -DgroupId=com.example -DartifactId=api -DarchetypeArtifactId=maven-archetype-quickstart -DinteractiveMode=false
  
mvn archetype:generate -DgroupId=com.example -DartifactId=service -DarchetypeArtifactId=maven-archetype-quickstart -DinteractiveMode=false  

Option 2: Manually Creating Modules

1. In your IDE, right-click the parent project → New → Module.
2. Select Maven and name them (e.g., api, service, repository).

Update Parent POM

Add the modules to the parent pom.xml:

<modules>  
    <module>api</module>  
    <module>service</module>  
    <module>repository</module>  
</modules>  

Step 3: Configure Dependencies Between Modules

Example: service Depends on repository

In service/pom.xml:

<dependencies>  
    <dependency>  
        <groupId>com.example</groupId>  
        <artifactId>repository</artifactId>  
        <version>1.0.0</version>  
    </dependency>  
</dependencies>  

Adding Spring Boot Dependencies

In the parent pom.xml, define dependency management:

<dependencyManagement>  
    <dependencies>  
        <dependency>  
            <groupId>org.springframework.boot</groupId>  
            <artifactId>spring-boot-dependencies</artifactId>  
            <version>3.2.0</version>  
            <type>pom</type>  
            <scope>import</scope>  
        </dependency>  
    </dependencies>  
</dependencyManagement>  

Then, in child modules (e.g., api), add required dependencies:

<dependencies>  
    <dependency>  
        <groupId>org.springframework.boot</groupId>  
        <artifactId>spring-boot-starter-web</artifactId>  
    </dependency>  
</dependencies>  

Step 4: Build and Run the Application

1. Build all modules:mvn clean install
2. Run the main Spring Boot class (in the api module, if it contains @SpringBootApplication).

Best Practices for Optimizing Multi-Module Projects

✅ Use Spring Boot Starters Wisely – Only include necessary dependencies in each module.

✅ Enable Caching in Maven/Gradle – Speeds up builds by reusing compiled modules.

✅ Layered JARs (for Docker) – Use Spring Boot’s layered JARs for efficient Docker builds.

✅ Module-Specific Configs – Keep application.yml in respective modules if needed.

✅ Avoid Circular Dependencies – Ensure modules have a clear hierarchy (e.g., api → service → repository).

✅ Use Spring Boot’s @ComponentScan Carefully – Define scan paths to avoid loading unnecessary beans.

✅ Profile-Based Builds – Use Maven/Gradle profiles to enable/disable modules based on environment.

Conclusion

A Spring Boot multi-module project improves maintainability, scalability, and build efficiency. By structuring your application into logical modules, you can optimize development workflows and reuse components across projects.

Follow the steps above, apply best practices, and enjoy a cleaner, more efficient Spring Boot development experience!

🔗 Further Reading:

• Spring Boot Multi-Module Guide
• Maven Multi-Module Docs

Happy Coding! 🚀