What is the lifecycle of Spring Beans?

1. Initialization:

   • Creating the Bean object.
   • Filling properties via Dependency Injection (@Autowired, @Value, etc.).
   • Executing the setBeanName() method (if the Bean implements BeanNameAware).
   • Executing the setBeanFactory() method (if the Bean implements BeanFactoryAware).
   • Executing the setApplicationContext() method (if the Bean implements ApplicationContextAware).
   • Executing the postProcessBeforeInitialization() methods of BeanPostProcessor.
   • Executing initialization methods:
     • Methods annotated with @PostConstruct.
     • The method specified in the initMethod attribute of the Bean definition.
     • The afterPropertiesSet() method (if the Bean implements InitializingBean).
   • Executing the postProcessAfterInitialization() methods of BeanPostProcessor.

2. Usage:

   • The Bean is ready for use.

3. Destruction (when the Spring context is closed):

   • Executing the postProcessBeforeDestruction() methods of DestructionAwareBeanPostProcessor.
   • Executing destruction methods:
     • Methods annotated with @PreDestroy.
     • The method specified in the destroyMethod attribute of the Bean definition.
     • The destroy() method (if the Bean implements DisposableBean).
   • Executing the postProcessAfterDestruction() methods of DestructionAwareBeanPostProcessor.

// Example of using lifecycle annotations
import javax.annotation.PostConstruct;
import javax.annotation.PreDestroy;

public class MySpringBean {

    private String myProperty;

    public void setMyProperty(String myProperty) {
        this.myProperty = myProperty;
        System.out.println("4. setMyProperty() called: " + myProperty); // Example of property initialization step
    }

    @PostConstruct
    public void customInitMethod() {
        System.out.println("9. @PostConstruct method called."); // Example of initialization step - @PostConstruct
    }

    public void anotherInitMethodFromConfig() {
        System.out.println("10. Custom initMethod from configuration called."); // Example of initialization step - initMethod
    }

    public void useBean() {
        System.out.println("12. Bean is in use. Property: " + myProperty); // Example of usage step
    }

    @PreDestroy
    public void customDestroyMethod() {
        System.out.println("14. @PreDestroy method called."); // Example of destruction step - @PreDestroy
    }

    public void anotherDestroyMethodFromConfig() {
        System.out.println("15. Custom destroyMethod from configuration called."); // Example of destruction step - destroyMethod in configuration
    }
}

Step	Description	Example
1	Creating Bean instance	new MySpringBean()
2	Filling properties (DI)	bean.setMyProperty("value")
3	BeanNameAware.setBeanName()	Called if the Bean implements BeanNameAware
4	BeanFactoryAware.setBeanFactory()	Called if the Bean implements BeanFactoryAware
5	ApplicationContextAware.setApplicationContext()	Called if the Bean implements ApplicationContextAware
6	BeanPostProcessor.postProcessBeforeInitialization()	Processing before initialization
7	InitializingBean.afterPropertiesSet()	Called if the Bean implements InitializingBean
8	@PostConstruct method	Method annotated with @PostConstruct
9	init-method from configuration	Method specified in the initMethod attribute
10	BeanPostProcessor.postProcessAfterInitialization()	Processing after initialization
11	Bean is ready for use	Calling Bean methods
12	DestructionAwareBeanPostProcessor.postProcessBeforeDestruction()	Processing before destruction
13	DisposableBean.destroy()	Called if the Bean implements DisposableBean
14	@PreDestroy method	Method annotated with @PreDestroy
15	destroy-method from configuration	Method specified in the destroyMethod attribute
16	DestructionAwareBeanPostProcessor.postProcessAfterDestruction()	Processing after destruction