juniorSpring
What is Dependency Injection in Spring?
Updated May 17, 2026
Short answer
DI is a pattern where dependencies are provided to a class instead of created internally.
Deep explanation
Spring supports constructor, setter, and field injection. Constructor injection is preferred because it ensures immutability and easier testing.
Real-world example
A service receives repository objects instead of creating database connections itself.
Common mistakes
- Using field injection everywhere which makes testing difficult.
Follow-up questions
- Which injection type is recommended?
- Why is DI important?