spring-boot

Expert guidance for Domain-Driven Design architecture and implementation. Use when designing complex business systems, defining bounded contexts, structuring domain models, choosing between modular monolith vs microservices, implementing aggregates/entities/value objects, or when users mention "DDD", "domain-driven design", "bounded context", "aggregate", "domain model", "ubiquitous language", "event storming", "context mapping", "domain events", "anemic domain model", strategic design, tactical patterns, or domain modeling. Helps make architectural decisions, identify subdomains, design aggregates, and avoid common DDD pitfalls.

Spring Boot 4 data layer implementation for Domain-Driven Design. Use when implementing JPA or JDBC aggregates, Spring Data repositories, transactional services, projections, or entity auditing. Covers aggregate roots with AbstractAggregateRoot, value object mapping, EntityGraph for N+1 prevention, and Spring Boot 4 specifics (JSpecify null-safety, AOT repositories). For DDD concepts and design decisions, see the domain-driven-design skill.

Spring Modulith 2.0 implementation for bounded contexts in Spring Boot 4. Use when structuring application modules, implementing @ApplicationModuleListener for event-driven communication, testing with Scenario API, enforcing module boundaries, or externalizing events to Kafka/AMQP. For modular monolith architecture decisions, see the domain-driven-design skill.

Spring Boot 4 observability with Actuator, Micrometer, and OpenTelemetry. Use when configuring health indicators, custom metrics, distributed tracing, production endpoint exposure, or Kubernetes/Cloud Run probes. Covers Actuator security, Micrometer Timer/Counter/Gauge patterns, and OpenTelemetry span customization.

Spring Security 7 implementation for Spring Boot 4. Use when configuring authentication, authorization, OAuth2/JWT resource servers, method security, or CORS/CSRF. Covers the mandatory Lambda DSL migration, SecurityFilterChain patterns, @PreAuthorize, and password encoding. For testing secured endpoints, see spring-boot-testing skill.

Spring Boot 4 testing strategies and patterns. Use when writing unit tests, slice tests (@WebMvcTest, @DataJpaTest), integration tests, Testcontainers with @ServiceConnection, security testing (@WithMockUser, JWT), or Modulith event testing with Scenario API. Covers the critical @MockitoBean migration from @MockBean.

Spring Boot 4 REST API implementation patterns. Use when creating REST controllers, request validation, exception handlers with ProblemDetail (RFC 9457), API versioning, content negotiation, or WebFlux reactive endpoints. Covers @RestController patterns, Bean Validation 3.1, global error handling, and Jackson 3 configuration.