Spring Boot Best Practices
Your goal is to help me write high-quality Spring Boot applications by following established best practices.
Project Setup & Structure
- Build Tool: Use Maven (
pom.xml) or Gradle (build.gradle) for dependency management.
- Starters: Use Spring Boot starters (e.g.,
spring-boot-starter-web, spring-boot-starter-data-jpa) to simplify dependency management.
- Package Structure: Organize code by feature/domain (e.g.,
com.example.app.order, com.example.app.user) rather than by layer (e.g., com.example.app.controller, com.example.app.service).
Dependency Injection & Components
- Constructor Injection: Always use constructor-based injection for required dependencies. This makes components easier to test and dependencies explicit.
- Immutability: Declare dependency fields as
private final.
- Component Stereotypes: Use
@Component, @Service, @Repository, and @Controller/@RestController annotations appropriately to define beans.
Configuration
- Externalized Configuration: Use
application.yml (or application.properties) for configuration. YAML is often preferred for its readability and hierarchical structure.
- Type-Safe Properties: Use
@ConfigurationProperties to bind configuration to strongly-typed Java objects.
- Profiles: Use Spring Profiles (
application-dev.yml, application-prod.yml) to manage environment-specific configurations.
- Secrets Management: Do not hardcode secrets. Use environment variables, or a dedicated secret management tool like HashiCorp Vault or AWS Secrets Manager.
Web Layer (Controllers)
- RESTful APIs: Design clear and consistent RESTful endpoints.
- DTOs (Data Transfer Objects): Use DTOs to expose and consume data in the API layer. Do not expose JPA entities directly to the client.
- Validation: Use Java Bean Validation (JSR 380) with annotations (
@Valid, @NotNull, @Size) on DTOs to validate request payloads.
- Error Handling: Implement a global exception handler using
@ControllerAdvice and @ExceptionHandler to provide consistent error responses.
Service Layer
- Business Logic: Encapsulate all business logic within
@Service classes.
- Statelessness: Services should be stateless.
- Transaction Management: Use
@Transactional on service methods to manage database transactions declaratively. Apply it at the most granular level necessary.
Data Layer (Repositories)
- Spring Data JPA: Use Spring Data JPA repositories by extending
JpaRepository or CrudRepository for standard database operations.
- Custom Queries: For complex queries, use
@Query or the JPA Criteria API.
- Projections: Use DTO projections to fetch only the necessary data from the database.
Logging
- SLF4J: Use the SLF4J API for logging.
- Logger Declaration:
private static final Logger logger = LoggerFactory.getLogger(MyClass.class);
- Parameterized Logging: Use parameterized messages (
logger.info("Processing user {}...", userId);) instead of string concatenation to improve performance.
Testing
- Unit Tests: Write unit tests for services and components using JUnit 5 and a mocking framework like Mockito.
- Integration Tests: Use
@SpringBootTest for integration tests that load the Spring application context.
- Test Slices: Use test slice annotations like
@WebMvcTest (for controllers) or @DataJpaTest (for repositories) to test specific parts of the application in isolation.
- Testcontainers: Consider using Testcontainers for reliable integration tests with real databases, message brokers, etc.
Security
- Spring Security: Use Spring Security for authentication and authorization.
- Password Encoding: Always encode passwords using a strong hashing algorithm like BCrypt.
- Input Sanitization: Prevent SQL injection by using Spring Data JPA or parameterized queries. Prevent Cross-Site Scripting (XSS) by properly encoding output.