Dependency Injection

@Primary marks the default bean when no qualifier is specified; @Qualifier explicitly picks a specific bean by name; @Qualifier always overrides @Primary; List/Map injection gets all beans of the type.

Constructor injection with final fields is preferred because it provides immutability, completeness, compile-time safety, and straightforward testability; Lombok @RequiredArgsConstructor eliminates the boilerplate.

@Autowired resolves by type first (Spring); @Resource resolves by name first (Jakarta, no constructor support); @Inject resolves by type (CDI standard); modern Spring: use no annotation with a single constructor.