spring-boot-best-practices

name	spring-boot-best-practices
description	Apply core coding standards, dependency injection, and configuration for Spring Boot 3. Use for Spring Boot application structure and DI/configuration; defer Spring Security hardening and test-specific setup to their focused skills.
metadata	{"triggers":{"files":["application.properties","**/*Service.java"],"keywords":["autowired","requiredargsconstructor","configuration-properties","slf4j"]}}

Spring Boot Best Practices

Priority: P0 (CRITICAL)

Implementation Guidelines

Dependency Injection (DI)

• Constructor Injection: ALWAYS use Constructor Injection for immutability. Use @RequiredArgsConstructor (Lombok) to reduce boilerplate. Mark all dependencies as final.
• Avoid @Autowired: NEVER use field injection. It prevents unit testing without Spring context and hides dependencies.

Configuration & Data

• Type-Safe Config: Use @ConfigurationProperties with Records (Java 17+) instead of @Value. Use Spring profile-specific files (e.g., application-dev.yml, application-prod.yml) and set active profile via SPRING_PROFILES_ACTIVE. Never hardcode secret values in properties files.
• Validation: Combine with @Validated and Jakarta Bean Validation (@NotNull, @NotEmpty) to fail fast at startup. Use application.yaml for structured configuration.
• DTOs: Use records as immutable DTOs to reduce boilerplate and ensure thread safety. Handle empty values with Optional to avoid NullPointerException.

Observability & Quality

• Error Handling: Implement @ControllerAdvice and ProblemDetails (RFC 7807) for standardized error responses.
• Logging: Use SLF4J with @Slf4j. Implement Structured Logging by logging arguments (log.info("id: {}", id)).
• Tooling: Mandate Spotless or Checkstyle for code formatting. Use sdkman to manage JDK 21+ versions.

Anti-Patterns

• No @Autowired on fields: Use constructor injection via @RequiredArgsConstructor.
• No Setters on dependencies: Declare all injected fields as final.
• No context.getBean(): Inject dependencies via constructor DI.
• No log-and-swallow: Rethrow or handle exceptions explicitly.

References

• Implementation Examples