Java / Micronaut Interview questions

Explain the lifecycle of a Micronaut bean?

A Micronaut bean moves through a well-defined set of stages between being requested and being destroyed, and several of them are extension points you can hook into.

graph TD A[Bean requested from ApplicationContext] --> B[Dependencies resolved via generated BeanDefinition] B --> C[Constructor invoked] C --> D[Field and method injection performed] D --> E[BeanCreatedEventListener beans notified] E --> F[PostConstruct method invoked] F --> G[Bean ready for use] G --> H[Context shutdown triggered] H --> I[PreDestroy method invoked] I --> J[BeanDestroyedEvent fired]

For a @Singleton, steps A through G happen once, at either eager startup for @Context-scoped beans or on first lookup for lazily initialized singletons; for @Prototype, the whole sequence repeats on every injection.

@PostConstruct and @PreDestroy give you hooks for setup and cleanup work, such as opening a connection pool or starting a background thread, and cleanly closing it, respectively, while implementing BeanCreatedEventListener<T> lets other beans observe or even wrap or replace an instance right after it's created, which is how some AOP-adjacent and instrumentation features are implemented.

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For a @Prototype-scoped bean, the full construction lifecycle: runs once for the whole application

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repeats on every injection or lookup

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never runs at all

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The @PreDestroy annotation is used for: initial validation before construction

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cleanup logic run when the bean is destroyed

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routing HTTP requests

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Java / Micronaut Interview questions

Explain the lifecycle of a Micronaut bean?

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