Spring Framework FAQ: Top Questions

@Qualifier is used to resolve the conflict when multiple beans of the same type are present in the Spring context and one needs to be injected.

🗺️ Step-by-Step:

1. Declare multiple beans of the same type with different names.
2. Use @Qualifier("beanName") to specify which one to inject.

📥 Example Input:

@Component("engineV6")
public class V6Engine implements Engine {}

@Component("engineV8")
public class V8Engine implements Engine {}

@Autowired
@Qualifier("engineV8")
private Engine engine;

🏆 Expected Output:

V8Engine instance is injected into the 'engine' field.

📘 Detailed Explanation:

• Avoids ambiguity: Prevents NoUniqueBeanDefinitionException.
• Fine-grained control: Explicitly defines which bean to use.

🛠️ Use Cases:

• Multiple data sources or strategy implementations.
• Injecting test/mock beans selectively in unit tests.