Multi Module Maven

Multi Module Maven

Use When

• Structuring multi-module Maven Spring Boot monorepos
• Spring Boot code generation or refactor where agent defaults would be wrong

Workflow

1. Confirm the change matches this skill's domain triggers before coding.
2. Follow the domain guide conventions and gotchas below — not generic Spring Boot defaults.
3. Apply project-specific response envelopes, DTO boundaries, and dependency injection rules.
4. Validate with targeted tests (slice, integration, or contract as appropriate).
5. Capture evidence before merge: tests, migration notes, or observability proof.

Required Checks

• Constructor injection used; no @Autowired field injection on new code
• Controllers return DTOs/envelopes — never raw JPA entities
• Business logic stays in @Service layer, not controllers or repositories
• Error handling uses project-standard envelope or RFC 9457 ProblemDetail

Domain Guide

Typical Structure

my-app/
├── pom.xml                  ← Parent POM (packaging = pom)
├── my-app-domain/           ← Pure Java domain — no Spring
│   └── pom.xml
├── my-app-application/      ← Use cases — depends on domain
│   └── pom.xml
├── my-app-infrastructure/   ← JPA, Redis, HTTP clients
│   └── pom.xml
└── my-app-web/              ← Spring Boot app, REST — depends on all above
    └── pom.xml

Parent POM

    com.example
    my-app
    1.0.0-SNAPSHOT
    pom

    
        my-app-domain
        my-app-application
        my-app-infrastructure
        my-app-web
    

    
        org.springframework.boot
        spring-boot-starter-parent
        3.3.0
    

    
    
        21
        1.6.0
        1.19.8
    

    
    
        
            
            
                com.example
                my-app-domain
                ${project.version}
            
            
                com.example
                my-app-application
                ${project.version}
            
            
            
                org.mapstruct
                mapstruct
                ${mapstruct.version}
            
        
    

    
    
        
            
                
                    org.apache.maven.plugins
                    maven-compiler-plugin
                    
                        ${java.version}
                        ${java.version}
                        
                            
                                org.projectlombok
                                lombok
                            
                            
                                org.mapstruct
                                mapstruct-processor
                                ${mapstruct.version}
                            
                        
                    
                
            
        
    

Child Module POM (domain — no Spring)

    
        com.example
        my-app
        1.0.0-SNAPSHOT
    

    my-app-domain

    
        
        
            org.projectlombok
            lombok
            true
        
    

Child Module POM (web — the runnable app)

    ...
    my-app-web

    
        
            com.example
            my-app-application
        
        
            com.example
            my-app-infrastructure
        
        
            org.springframework.boot
            spring-boot-starter-web
        
    

    
        
            
            
                org.springframework.boot
                spring-boot-maven-plugin
            
        
    

Dependency Rules

| Module | Can depend on | Cannot depend on | |--------|---------------|------------------| | domain | Nothing | Everything | | application | domain | infrastructure, web | | infrastructure | domain, application | web | | web | All modules | — |

Gotchas

• Agent puts spring-boot-maven-plugin in parent POM — only in the runnable module
• Agent adds ` in parent instead of ` — adds to all modules' classpath
• Agent creates circular dependencies between modules — enforce the dependency direction above
• Agent imports Spring in domain module — domain must be framework-free
• Agent uses ${project.version} for inter-module versions — correct, but update parent version to update all

Examples And Templates

See \examples/\ for side-by-side good vs bad patterns agents commonly get wrong. See \ emplates/\ for copy-paste starters aligned with this skill.

Decision Framework

• Prefer Spring Boot 3.x and Spring AI 1.0 GA artifact coordinates — reject pre-GA dead names.
• Use constructor injection and immutable dependencies by default.
• Keep domain content in services; controllers are HTTP adapters only.
• Externalize prompts, API keys, and migration scripts — never hardcode secrets.

Common Rationalizations And Rebuttals

• "@Autowired fields are fine for prototypes." -> Field injection hides dependencies and breaks testability; use constructor injection.
• "The agent knows Spring Boot." -> Agents default to outdated patterns; follow this skill's gotchas and GA coordinates.
• "We can skip Flyway for this column." -> Manual DDL drifts from environments; use versioned migrations.

Evidence Pack

• Test output for changed endpoints, services, or migrations
• Diff showing DTO boundaries and no entity leakage in API layer
• Dependency or coordinate list confirming GA artifact names
• Observability or security checklist for auth/AI changes

Exit Criteria

• Generated code matches project layering and naming conventions
• No pre-GA Spring AI or MCP artifact names in pom/build files
• Tests pass for happy path and at least one failure/edge case

Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: vaquarkhan
• Source: vaquarkhan/Fullstack-development-agent-skills
• License: MIT

Install and usage instructions live in the source repository linked above.