java-spring-boot-patterns

Organize code into controller, service, repository, model, dto, exception, and config packages under your base package. Controllers handle HTTP, services contain business logic with @Transactional, and repositories extend JpaRepository for data access.

Annotate the class with @RestController and @RequestMapping with a versioned path like /api/v1/users. Return ResponseEntity with 200 for reads, 201 with a Location header for creates, and 204 for deletes, using constructor injection for the service.

Controllers should return DTOs, never entities, to avoid exposing internal model structure. Use Java records for request and response DTOs with validation annotations, and MapStruct mappers to convert between entities and DTOs.

Create a class annotated with @RestControllerAdvice containing @ExceptionHandler methods for each exception type. Return a consistent ErrorResponse record with a code and message, mapping custom exceptions like ResourceNotFoundException to appropriate HTTP statuses.

@WebMvcTest loads only the web layer with mocked services for fast controller tests using MockMvc. @SpringBootTest starts the full application context for integration tests, often combined with Testcontainers for a real database.

Use native queries sparingly, only when derived queries or JPQL @Query cannot express the logic. Prefer derived query methods and existsBy checks, and use @EntityGraph to optimize fetching instead of writing native SQL.