What happens at application startup if several beans match one type?

If multiple beans are suitable for injection by the same type (for example, an interface) when starting a Spring application, a conflict will occur, and the context will not be able to unambiguously select which bean to use. As a result, the application will throw a NoUniqueBeanDefinitionException.

To resolve this issue, you can:

• Use the @Primary annotation on one of the beans to indicate the preferred one.
• Inject the bean by name using @Qualifier.
• Reconsider the design to avoid ambiguity.

Example:

@Component
@Primary
public class ServiceImpl1 implements MyService {}

@Component
public class ServiceImpl2 implements MyService {}

// Injection
@Autowired
private MyService myService; // will inject ServiceImpl1