Spring Boot (Java) Guide

Applies to: Spring Boot 3.x, Java 17+, REST APIs, Microservices, Enterprise Applications

Core Principles

1. Convention Over Configuration: Leverage Spring Boot auto-configuration; override only when necessary
2. Layered Architecture: Controller -> Service -> Repository with clear separation of concerns
3. DTOs at Boundaries: Never expose JPA entities in API responses; use records as DTOs
4. Constructor Injection: Use @RequiredArgsConstructor or explicit constructors; never field injection
5. Externalized Config: All configuration via application.yml with profile-specific overrides
6. Database Migrations: Schema changes through Flyway or Liquibase; never ddl-auto=update in production

Guardrails

Architecture Rules

• Controllers handle HTTP concerns only (validation, status codes, response mapping)
• Services contain business logic and transaction boundaries