spring-boot-3

Constructor-based dependency injection improves testability by making dependencies explicit and immutable. Spring Boot 3 enforces this pattern to decouple components and simplify unit testing without reflection or mocking frameworks.

@ConfigurationProperties with validation creates typed, strongly-checked configuration contracts. This approach centralizes property binding, catches misconfigurations at startup, and replaces scattered @Value annotations with maintainable, validated objects.

@Transactional at the service layer ensures reliable transaction management across database operations. Placing it on service methods—not controllers—maintains clean separation, prevents nested transactions, and guarantees consistent commit or rollback behavior.

Yes, Spring Boot 3 supports constructor injection in @RestController classes. This pattern improves testability by making controller dependencies explicit and enables Spring to automatically wire services, repositories, and configuration objects without field injection.

Spring Boot 3 supports standard Jakarta Bean Validation annotations (@NotNull, @Min, @Pattern, @Email) on @ConfigurationProperties fields. Validation runs at application startup, catching invalid configurations early and providing clear error messages.

Avoid @Transactional on controllers because they handle HTTP concerns, not persistence logic. Place transactions at the service layer where business logic lives; controllers should coordinate services and handle responses, keeping concerns separated for clarity and maintainability.