Spring Boot - Spring Modulith

Apply Spring Modulith guidelines for Spring Boot modular monoliths.

What is covered in this Skill?

Spring Modulith BOM and starter dependency selection
Business-capability package structure for application modules
ApplicationModules verification and architecture tests
Named interfaces and explicit allowed dependencies
Domain events for loose coupling between modules
@ApplicationModuleTest and Scenario-based module integration tests
Generated module documentation, actuator exposure, and observability
Event publication registry choices for reliable domain events

Scope: Apply recommendations based on the reference rules, official Spring Modulith documentation, and good/bad examples.

Constraints

Before applying Spring Modulith changes, ensure the project compiles. After improvements, run full verification including module structure tests.

MANDATORY: Run ./mvnw compile or mvn compile before applying any change
PRECONDITION: The project must be a Spring Boot application; for non-Boot Java modularity use architecture or design skills instead
BASELINE: Align dependency choices with Spring Boot 4.0.x and the Spring Modulith compatibility matrix
SAFETY: If compilation fails, stop immediately
VERIFY: Run ./mvnw clean verify or mvn clean verify after applying improvements
BEFORE APPLYING: Read the reference for detailed rules, good/bad patterns, and official documentation links

When to use this skill

Add Spring Modulith to a Spring Boot application
Review Spring Modulith module boundaries
Improve modular monolith architecture in Spring Boot
Add @ApplicationModuleTest tests
Generate Spring Modulith documentation
Refactor Spring Boot modules with Spring Modulith

Workflow

Read reference and inspect project structure

Read references/305-frameworks-spring-boot-modulith.md and inspect the Spring Boot version, Maven dependencies, main application package, and current package/module boundaries.

Model application modules

Identify business-capability modules, public APIs, internal packages, named interfaces, and intentional allowed dependencies.

Apply framework-aligned changes

Add or refine Spring Modulith dependencies, package annotations, architecture verification tests, domain events, and module tests following the reference patterns.

Run verification and report results

Execute appropriate build/tests, especially ApplicationModules.verify() and @ApplicationModuleTest coverage, then summarize changes, risks, and follow-up module design work.

Reference

For detailed guidance, examples, and constraints, see references/305-frameworks-spring-boot-modulith.md.