1. Introduction:
In Spring Boot, @Qualifier and @Bean annotations work together to resolve ambiguity when multiple beans of the same type exist in the Spring container. @Qualifier is used to specify the exact bean to be injected, and @Bean is used to define custom beans.
2. @Qualifier Annotation:
@Qualifier is used to specify the name of the bean to be injected when there are multiple beans of the same type. It is commonly used in conjunction with constructor injection, field injection, or method injection.
Example:
In this example, if there are multiple beans of type MyBean in the Spring context, @Qualifier("customBean") specifies that the bean with the name “customBean” should be injected.
3. @Bean Annotation:
@Bean is used to define custom beans in a Spring Boot application. When a method is annotated with @Bean, the return value of that method is registered as a bean in the Spring container.
Example:
In this example, the myBean() method in the MyConfiguration class is annotated with @Bean, creating a bean named “customBean” of type MyBean.
4. Using @Qualifier with @Autowired:
When dealing with multiple beans of the same type, you can use @Qualifier in conjunction with @Autowired to specify which bean should be injected.
Example:
In this example, the AnotherService class injects a specific bean (customBean) of type MyBean using @Qualifier.
5. Conclusion:
The @Qualifier and @Bean annotations in Spring Boot provide a way to deal with scenarios where multiple beans of the same type exist in the Spring container. @Qualifier helps specify the exact bean to be injected, and @Bean allows you to define custom beans.
This tutorial covers the basics, but there are more advanced use cases and features to explore. Refer to the official Spring documentation for further details:
Feel free to ask if you have any specific questions or need further clarification on any topic!
