@PostConstruct and @PreDestroy in Spring Boot - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of the @PostConstruct annotation in Spring Boot?

It marks a method to be executed once immediately after the bean's initialization and dependency injection are complete.

beginner

When is a method annotated with @PreDestroy called in a Spring Boot application?

It is called just before the bean is removed from the container, typically during application shutdown, to allow cleanup.

intermediate

Can @PostConstruct and @PreDestroy methods have parameters?

No, methods annotated with @PostConstruct and @PreDestroy must have no parameters and return void.

intermediate

How do @PostConstruct and @PreDestroy relate to the bean lifecycle in Spring Boot?

They provide hooks to run custom code right after bean creation (@PostConstruct) and right before bean destruction (@PreDestroy), managing setup and cleanup.

intermediate

What happens if you forget to add @PreDestroy on a cleanup method in Spring Boot?

The cleanup code won't run automatically on shutdown, which may cause resource leaks like open connections or files.

Which annotation runs a method after Spring Boot bean initialization?

A @Component

B @PreDestroy

C @Autowired

D @PostConstruct

@PostConstruct runs after the bean is fully initialized.

What is the correct signature for a method annotated with @PreDestroy?

A public void cleanup()

B public int cleanup(int code)

C public String cleanup(String msg)

D public void cleanup(String param)

@PreDestroy methods must have no parameters and return void.

When is a @PreDestroy method executed in Spring Boot?

A Before bean destruction

B After bean initialization

C During bean creation

D When a bean is injected

@PreDestroy runs just before the bean is destroyed.

What happens if you don't use @PostConstruct for initialization code?

A The code runs before bean creation

B The code runs after bean destruction

C The code might not run automatically after bean setup

D The code runs multiple times

Without @PostConstruct, initialization code won't run automatically after dependencies are injected.

Which of these is NOT true about @PostConstruct and @PreDestroy?

A They help manage bean lifecycle events

B They can have parameters in their methods

C @PostConstruct runs after dependencies are injected

D @PreDestroy runs before bean removal

Methods annotated with these must have no parameters.

Explain how @PostConstruct and @PreDestroy annotations help manage a Spring Boot bean's lifecycle.

Think about when you want to prepare and clean up resources in your app.

Describe what could happen if you omit @PreDestroy on a method that closes resources in a Spring Boot app.

Consider what happens if you never close a door after entering a room.