How do you create a multi-module Spring Boot project?

Table of Contents

• Introduction
• Steps to Create a Multi-Module Spring Boot Project
  • 1. Create the Parent Project
    • Create a Parent pom.xml
  • Key Components of the Parent pom.xml:
  • 2. Create the Child Modules
    • Create module1/pom.xml
    • Create module2/pom.xml
  • Key Points:
  • 3. Build and Run the Multi-Module Project
  • 4. Managing Dependencies Between Modules
• Conclusion

Introduction

In large-scale enterprise applications, it’s common to break down a monolithic Spring Boot application into smaller, modular components for easier maintenance, scalability, and reusability. A multi-module Spring Boot project allows you to structure your application into multiple submodules or components, each responsible for a specific feature or set of features. This modular approach simplifies dependency management, testing, and overall project maintainability.

In this guide, we will walk you through the steps of creating a multi-module Spring Boot project using Maven. We will cover how to configure the parent-child module relationship, organize the project structure, and manage dependencies effectively.

Steps to Create a Multi-Module Spring Boot Project

1. Create the Parent Project

The parent project in a multi-module Spring Boot project acts as the central point for configuration and dependency management. This parent project typically holds common configurations and dependencies for the child modules. The parent project defines the version of Spring Boot and other dependencies that will be inherited by the child modules.

Create a Parent pom.xml

To start, create a directory for your parent project, e.g., spring-boot-multi-module, and then create the following pom.xml file for the parent project.

Parent **pom.xml** Example:

Key Components of the Parent pom.xml:

1. Packaging type: The parent project’s packaging type is set to pom because it’s not meant to be built into a JAR or WAR file. It's just a parent for the child modules.
2. Modules: The <modules> section lists the child modules (e.g., module1, module2, module3) that are part of this project.
3. Dependency Management: The spring-boot-dependencies BOM (Bill of Materials) is imported to manage consistent dependency versions across all modules.
4. Common Dependencies: Any dependencies shared by all child modules, such as Spring Boot starters, can be listed in the <dependencies> section of the parent.

2. Create the Child Modules

Each child module will represent a specific part of the application, such as a web layer, service layer, or data layer. These child modules inherit from the parent pom.xml, which ensures that they use the same version of Spring Boot and any common dependencies.

Create module1/pom.xml

Create module2/pom.xml

Key Points:

• Each child module defines a <parent> section pointing to the parent POM, ensuring that it inherits dependencies and versions.
• The child modules only declare the dependencies they require. Common dependencies like Spring Boot starters are inherited from the parent POM.

3. Build and Run the Multi-Module Project

To build the entire multi-module Spring Boot project, navigate to the parent project directory and run the following Maven command:

This command will build the parent project and all of its child modules. Each child module will be packaged as a JAR file, and the final build will include the artifacts for all modules.

To run the entire application, you can specify the main class of the module that you want to run, for example, module1:

This command runs the Spring Boot application from the specified module (module1).

4. Managing Dependencies Between Modules

If a child module depends on another child module, you can declare that dependency in the child module’s <dependencies> section.

For example, if module2 needs to depend on module1, you would declare it like this:

**module2/pom.xml** (with dependency on **module1**):

Maven will resolve the dependency by building and packaging module1 before module2.

Conclusion

Creating a multi-module Spring Boot project involves setting up a parent-child module structure using Maven. By organizing your application into modular components, you improve maintainability, scalability, and dependency management. The parent pom.xml file acts as the central point for common configuration, such as dependency versions and shared dependencies, while child modules focus on their specific functionality.

This setup allows you to:

• Reuse dependencies and configuration across multiple modules.
• Simplify the management of version conflicts.
• Build and deploy each module independently or together, depending on your needs.

With a well-organized multi-module Spring Boot project, you can develop large, complex applications in a maintainable and scalable way.