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A Spring-managed bean moves through creation and dependency population, initialization callbacks, post-processing, and—when managed destruction is triggered—destruction callbacks. Post-processors can expose a proxy instead of the original instance, while the separate Lifecycle interface handles context-driven start and stop signals. These are Spring Framework container behaviors beneath Spring Boot; ordinary Java objects that Spring does not manage do not automatically follow this sequence.
How a managed bean moves through the container
Spring starts with bean definitions: metadata describing how to create and configure beans, including their class, scope, dependencies, properties, and any configured initialization or destruction methods. A container can also register existing objects rather than create them through the ordinary definition path. See the Spring bean overview.
- Instantiation and population: The container creates the instance, then populates configured dependencies and properties.
- Before-initialization processing: Registered
BeanPostProcessorimplementations receive the populated bean throughpostProcessBeforeInitialization. A processor can return the same instance or a wrapper. - Initialization callbacks: Spring invokes applicable callbacks in the documented order:
@PostConstruct,InitializingBean.afterPropertiesSet(), then a configured custom init method. - After-initialization processing: The container calls
postProcessAfterInitialization. A processor may return a wrapper or proxy; that processed object can be the one exposed for application use. - Managed destruction: When destruction is triggered for a bean whose lifecycle the container manages, applicable callbacks run in this order:
@PreDestroy,DisposableBean.destroy(), then a configured destroy method.
This is the usual managed-bean path, not a claim that every object in a Java application is a bean or that every bean is created eagerly. Special creation paths can differ: the BeanPostProcessor API documents a case in which its callback is invoked after an InstantiationAwareBeanPostProcessor.postProcessBeforeInstantiation short-circuit. Consult the BeanPostProcessor API for that exception.
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A BeanPostProcessor works with bean instances, not the bean-definition blueprint. Use a BeanFactoryPostProcessor when the task is to change bean-definition metadata. Post-processors apply within their own container; an application context detects post-processor beans automatically. The Spring container extension-point documentation explains their scope and role.
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Post-processors themselves, along with beans directly referenced by them, are instantiated early. That timing matters when declaring one with @Bean: use a factory method with a return type that clearly identifies the post-processor, make the method static, and keep it dependency-free where practical. Otherwise, early creation of the configuration class or related beans can leave them without full post-processing, including auto-proxying.
Choosing initialization and destruction callbacks
| Option | Where it is declared | Trade-off or use |
|---|---|---|
@PostConstruct / @PreDestroy |
Annotations on the bean class | Annotation-based callbacks that avoid coupling the bean directly to Spring callback interfaces; Spring generally recommends them for modern applications. |
InitializingBean.afterPropertiesSet() / DisposableBean.destroy() |
Implemented on the bean class | Directly couples the class to Spring interfaces. They are valid options, but use a less coupled mechanism when it works. |
| Custom init/destroy methods | Configured in bean metadata or on an @Bean declaration |
Lets a POJO use ordinary methods without implementing Spring callback interfaces. |
The callback order and Spring’s guidance are documented under Customizing the Nature of a Bean. For Java configuration, @Bean supports these callbacks through initMethod and destroyMethod; see Using the @Bean Annotation.
When @Bean infers a destruction method
By default, Spring infers a public close or shutdown method as a destruction callback for an @Bean method. If a resource is managed elsewhere—for example, an externally managed JNDI DataSource—that inferred callback may be inappropriate. Set @Bean(destroyMethod = "") to disable the inference when external ownership requires it.
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Initialization and destruction callbacks belong to an individual bean’s managed lifecycle. Spring’s Lifecycle interface serves a different purpose: a bean implementing it can receive start() and stop() signals coordinated by the application context. The context delegates those signals through a LifecycleProcessor when it receives start or stop events. Implementing Lifecycle does not replace @PostConstruct, @PreDestroy, or other per-bean callbacks. The distinction is covered in the Spring bean lifecycle reference.
Why the application may use a proxy
Because a post-processor can replace the instance it receives, the object ultimately exposed by the container need not be the original object created by the container. Spring AOP infrastructure commonly uses post-processing to wrap beans with proxies. This is why debugging may show an application-facing proxy even though the target bean was initialized earlier in the sequence.
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