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Beyond construction, beans pass through phases: the container instantiates them, injects dependencies, runs initialization callbacks, serves requests, then runs destruction callbacks at shutdown.

Hooking into these phases lets you set up and clean up resources reliably.

A constructor runs before dependencies are injected when using setter/field injection, so collaborators may still be null. Initialization that depends on injected beans belongs in a post-construction callback, not the constructor.

With constructor injection the dependencies are present, but lifecycle callbacks still give a clear, intent-revealing place for setup.

A method annotated @PostConstruct runs once after the bean is fully constructed and all dependencies are injected. Use it for warm-up tasks like priming a cache or validating state.

A method annotated @PreDestroy runs once when the context is shutting down, before the bean is destroyed. Use it to release resources like connections, thread pools, or file handles.

Implementing InitializingBean provides afterPropertiesSet, called after dependencies are set. It works but couples your class to Spring’s API, so annotations are usually preferred.

Symmetrically, DisposableBean supplies a destroy method for cleanup. Like InitializingBean, it ties you to Spring interfaces.

For beans you create with @Bean (often third-party types), specify lifecycle methods by name. This keeps the external class free of Spring annotations.

When several mechanisms are present, the init order is: @PostConstruct first, then InitializingBean.afterPropertiesSet, then a custom initMethod. Destruction mirrors this with @PreDestroy first.

For modern code, prefer the JSR-250 annotations @PostConstruct and @PreDestroy. They are concise, framework-neutral, and clearly express intent without coupling to Spring interfaces.

The container does not call destruction callbacks for prototype beans — it hands them off and forgets them. If a prototype holds resources, you are responsible for releasing them yourself.

Spring Boot triggers destruction callbacks during a clean shutdown (for example on SIGTERM). Combined with graceful shutdown settings, this lets in-flight work finish and resources close cleanly before exit.

Test your understanding of lifecycle callbacks.

Lifecycle callbacks manage setup and cleanup.

• @PostConstruct runs after dependencies are injected
• @PreDestroy runs before shutdown for cleanup
• InitializingBean/DisposableBean work but couple to Spring
• Use initMethod/destroyMethod for @Bean-created types
• Prototype destruction is your responsibility