What is the Use of @Bean Annotation in Spring?

The @Bean annotation in Spring is used to declare a method that returns a Spring bean, which is managed by the Spring IoC (Inversion of Control) container. It is typically used in configuration classes annotated with @Configuration.

How @Bean Internally Works

1. Spring Configuration Class:
   • When a class is annotated with @Configuration, it indicates that the class contains bean definitions.
   • During the application startup, Spring scans the @Configuration classes and processes their @Bean methods.
2. Bean Creation and Management:
   • Each @Bean method is executed, and the returned object is registered as a bean in the Spring container.
   • By default, beans are singleton scoped, meaning the same instance is reused for every request to the container.
3. Proxy Mechanism:
   • Spring uses CGLIB proxies for classes annotated with @Configuration. This ensures that even if an @Bean method is called directly from within the configuration class, the proxy intercepts the call and retrieves the bean from the container instead of creating a new instance.

Possible Ways to Use @Bean

1. name

• Description: Specifies one or more names for the bean. If not provided, the method name is used as the default bean name.

• Type: String[]

• Use Case:

  • To assign custom names or aliases to a bean, which can be useful when multiple beans of the same type exist in the application context.

• Example:

  
  @Bean(name = {"myServiceBean", "serviceAlias"})
  public MyService myService() {
      return new MyService();
  }
  

  • Usage: You can refer to this bean using either myServiceBean or serviceAlias.

2. initMethod

• Description: Specifies a method to call after the bean has been initialized and dependencies injected.

• Type: String

• Use Case:

  • To perform custom initialization logic after the bean has been created.

• Example:

  
  @Bean(initMethod = "init")
  public MyService myService() {
      return new MyService();
  }
  

  • MyService Class:

    
    public class MyService {
        public void init() {
            System.out.println("Bean is initialized");
        }
    }