solid-java

SOLID Java enforces a modular architecture for Java 25+ (current LTS): every feature lives under `modules/[feature]/` (controllers, services, repositories, interfaces, models/DTOs) with shared code in `modules/core/`, interfaces live only in `modules/[feature]/interfaces/`, controllers stay under 50 lines and delegate to services, records are used for DTOs and sealed types for restricted hierarchies, and every public method carries Javadoc.

Before writing any new code it requires a DRY check against modules/core/services and modules/core/interfaces. See solid-principles.md for the overview, the per-principle references for SRP/OCP/LSP/ISP/DIP detail, and the templates for module/service/interface/repository/error/test scaffolding.

SOLID Java - Modular Architecture

Agent Workflow (MANDATORY)

Before ANY implementation, spawn 3 agents in parallel, one Agent call each with a name:

1. fuse-ai-pilot:explore-codebase - Analyze existing architecture
2. fuse-ai-pilot:research-expert - Verify Java docs via Context7
3. fuse-ai-pilot:sniper - Post-implementation validation

---

DRY - Reuse Before Creating (MANDATORY)

Before writing ANY new code:

1. Grep the codebase for similar interfaces, services, or logic
2. Check shared locations: modules/core/services/, modules/core/interfaces/
3. If similar code exists -> extend/reuse instead of duplicate
4. If code will be used by 2+ features -> create it in modules/core/

---

Architecture (Modules MANDATORY)

Layer	Location	Max Lines
Controllers	modules/[feature]/controllers/	50
Services	modules/[feature]/services/	100
Repositories	modules/[feature]/repositories/	100
Interfaces	modules/[feature]/interfaces/	30
Models/DTOs	modules/[feature]/models/	50
Shared	modules/core/{services,interfaces,models}/	-

NEVER use flat src/ structure - always modules/[feature]/

---

Critical Rules (MANDATORY)

Rule	Value
File limit	100 lines (split at 90)
Controllers	< 50 lines, delegate to services
Interfaces	modules/[feature]/interfaces/ ONLY
Javadoc	Every public method documented
Records	Use for DTOs (Java 16+)
Sealed	Use for restricted hierarchies (Java 17+)

---

Reference Guide

Concepts

Topic	Reference	When to consult
SOLID Overview	solid-principles.md	Quick reference
SRP	single-responsibility.md	Fat classes
OCP	open-closed.md	Adding providers
LSP	liskov-substitution.md	Contracts
ISP	interface-segregation.md	Fat interfaces
DIP	dependency-inversion.md	Injection
Architecture	architecture-patterns.md	Modular patterns

Templates

Template	When to use
module.md	Feature module structure
service.md	Business logic service
interface.md	Contract definition
repository.md	Data access layer
error.md	Custom exceptions
test.md	Unit tests with mocks

---

Forbidden

Anti-Pattern	Fix
Files > 100 lines	Split at 90
Interfaces in impl files	Move to interfaces/ directory
new ConcreteClass() in services	Use dependency injection
Flat src/ structure	Use modules/[feature]/
God classes	Split by responsibility