Spring Boot CRUD Patterns

Overview

Deliver feature-aligned CRUD services that separate domain, application, presentation, and infrastructure layers while preserving Spring Boot 3.5+ conventions. This skill distills the essential workflow and defers detailed code listings to reference files for progressive disclosure.

When to Use

• Implement REST endpoints for create/read/update/delete workflows backed by Spring Data JPA.
• Refine feature packages following DDD-inspired architecture with aggregates, repositories, and application services.
• Introduce DTO records, request validation, and controller mappings for external clients.
• Diagnose CRUD regressions, repository contracts, or transaction boundaries in existing Spring Boot services.
• Trigger phrases: "implement Spring CRUD controller", "refine feature-based repository", "map DTOs for JPA aggregate", "add pagination to REST list endpoint".

Prerequisites

• Java 17+ project using Spring Boot 3.5.x (or later) with spring-boot-starter-web and spring-boot-starter-data-jpa.
• Constructor injection enabled (Lombok @RequiredArgsConstructor or explicit constructors).
• Access to a relational database (Testcontainers recommended for integration tests).
• Familiarity with validation (jakarta.validation) and error handling (ResponseStatusException).

Quickstart Workflow

1. Establish Feature Structure
   Create feature/<name>/ directories for domain, application, presentation, and infrastructure.
2. Model the Aggregate
   Define domain entities and value objects without Spring dependencies; capture invariants in methods such as create and update.
3. Expose Domain Ports
   Declare repository interfaces in domain/repository describing persistence contracts.
4. Provide Infrastructure Adapter
   Implement Spring Data adapters in infrastructure/persistence that map domain models to JPA entities and delegate to JpaRepository.
5. Implement Application Services
   Create transactional use cases under application/service that orchestrate aggregates, repositories, and mapping logic.
6. Publish REST Controllers
   Map DTO records under presentation/rest, expose endpoints with proper status codes, and wire validation annotations.
7. Validate with Tests
   Run unit tests for domain logic and repository/service tests with Testcontainers for persistence verification.

Consult references/examples-product-feature.md for complete code listings that align with each step.

Implementation Patterns

Domain Layer

• Define immutable aggregates with factory methods (Product.create) to centralize invariants.
• Use value objects (Money, Stock) to enforce type safety and encapsulate validation.
• Keep domain objects framework-free; avoid @Entity annotations in the domain package when using adapters.

Application Layer

• Wrap use cases in @Service classes using constructor injection and @Transactional.
• Map requests to domain operations and persist through domain repositories.
• Return response DTOs or records produced by dedicated mappers to decouple domain from transport.

Infrastructure Layer

• Implement adapters that translate between domain aggregates and JPA entities; prefer MapStruct or manual mappers for clarity.
• Configure repositories with Spring Data interfaces (e.g., JpaRepository<ProductEntity, String>) and custom queries for pagination or batch updates.
• Externalize persistence properties (naming strategies, DDL mode) via application.yml; see references/spring-official-docs.md.

Presentation Layer

• Structure controllers by feature (ProductController) and expose REST paths (/api/products).
• Return ResponseEntity with appropriate codes: 201 Created on POST, 200 OK on GET/PUT/PATCH, 204 No Content on DELETE.
• Apply @Valid on request DTOs and handle errors with @ControllerAdvice or ResponseStatusException.

Validation and Observability

• Write unit tests that assert domain invariants and repository contracts; refer to references/examples-product-feature.md integration test snippets.
• Use @DataJpaTest and Testcontainers to validate persistence mapping, pagination, and batch operations.
• Surface health and metrics through Spring Boot Actuator; monitor CRUD throughput and error rates.
• Log key actions at info for lifecycle events (create, update, delete) and use structured logging for audit trails.

Best Practices

• Favor feature modules with clear boundaries; colocate domain, application, and presentation code per aggregate.
• Keep DTOs immutable via Java records; convert domain types at the service boundary.
• Guard write operations with transactions and optimistic locking where concurrency matters.
• Normalize pagination defaults (page, size, sort) and document query parameters.
• Capture links between commands and events where integration with messaging or auditing is required.

Constraints and Warnings

• Avoid exposing JPA entities directly in controllers to prevent lazy-loading leaks and serialization issues.
• Do not mix field injection with constructor injection; maintain immutability for easier testing.
• Refrain from embedding business logic in controllers or repository adapters; keep it in domain/application layers.
• Validate input aggressively to prevent constraint violations and produce consistent error payloads.
• Ensure migrations (Liquibase/Flyway) mirror aggregate evolution before deploying schema changes.

References

• HTTP method matrix, annotation catalog, DTO patterns.
• Progressive examples from starter to advanced feature implementation.
• Excerpts from official Spring guides and Spring Boot reference documentation.
• Python generator to scaffold CRUD boilerplate from entity spec. Usage: python skills/spring-boot/spring-boot-crud-patterns/scripts/generate_crud_boilerplate.py --spec entity.json --package com.example.product --output ./generated
• Templates required: place .tpl files in skills/spring-boot/spring-boot-crud-patterns/templates/ or pass --templates-dir <path>; no fallback to built-ins. See templates/README.md.
• Usage guide: references/generator-usage.md
• Example spec: skills/spring-boot/spring-boot-crud-patterns/assets/specs/product.json
• Example with relationships: skills/spring-boot/spring-boot-crud-patterns/assets/specs/product_with_rel.json