spring-boot-dependency-injection
Constructor-first dependency injection patterns for Spring Boot with optional collaborator handling and bean selection strategies.
- Prioritizes constructor injection to keep dependencies explicit, immutable, and testable without Spring context.
- Handles optional dependencies through guarded setters, ObjectProvider, and deterministic no-op defaults.
- Resolves bean ambiguity using @Primary, @Qualifier, profiles, and conditional annotations (@ConditionalOnProperty, @ConditionalOnMissingBean).
- Includes validation workflows covering unit tests with mocks, slice tests, and Spring context verification before integration testing.
- Requires Java 17+ and Spring Boot 3.5.x; provides reference materials and progressive examples from basic constructor injection to multi-module configurations.
Spring Boot Dependency Injection
Overview
Provides constructor-first dependency injection patterns for Spring Boot:
- mandatory collaborators via constructor injection
- optional collaborators via
ObjectProvideror no-op fallbacks - bean selection via
@Primaryand@Qualifier - validation via minimal context tests before full integration
When to Use
Use this skill when:
- creating a new
@Service,@Component,@Repository, or@Configurationclass - replacing field injection in legacy Spring code
- resolving multiple beans of the same type with qualifiers or primary beans
- handling optional features, adapters, or integrations without null-driven wiring
- reviewing circular dependencies or brittle context startup failures
- preparing code for direct constructor-based unit testing
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