@PostConstruct and @PreDestroy in Spring Boot - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

When is a method annotated with @PostConstruct called?

In a Spring Boot application, what is the correct time when a method annotated with @PostConstruct is executed?

A Right after the bean is fully initialized and dependencies are injected, before the bean is ready to use.

B Only when the application context is closed.

C After the bean is destroyed and removed from the context.

D Before the bean is created and dependencies are injected.

💡 Hint

Think about when you want to run setup code after all dependencies are ready.

The @PostConstruct method runs once the bean is fully created and all dependencies are injected. It is used to perform initialization tasks before the bean is used.

❓ component_behavior

intermediate

What happens when a method is annotated with @PreDestroy?

In a Spring Boot bean, when is a method annotated with @PreDestroy executed?

A After the bean is fully initialized and ready to use.

B When the bean is created and dependencies are injected.

C When the application starts.

D Right before the bean is destroyed and removed from the Spring context.

💡 Hint

Think about cleanup tasks before the bean disappears.

The @PreDestroy method runs just before the bean is destroyed by the Spring container. It is used to release resources or perform cleanup.

📝 Syntax

advanced

Identify the correct usage of @PostConstruct in a Spring Boot bean

Which of the following code snippets correctly uses @PostConstruct in a Spring Boot component?

A

public class MyBean {
  @PostConstruct
  public void init(String param) {
    System.out.println(param);
  }
}

B

public class MyBean {
  @PostConstruct
  private int init() {
    return 1;
  }
}

C

public class MyBean {
  @PostConstruct
  public void init() {
    System.out.println("Bean initialized");
  }
}

D

public class MyBean {
  @PostConstruct
  public static void init() {
    System.out.println("Static init");
  }
}

💡 Hint

Remember the method must be void, no parameters, and non-static.

The @PostConstruct method must be void, have no parameters, and not be static. Option C meets all these requirements.

🔧 Debug

advanced

Why does the @PreDestroy method not run in this Spring Boot application?

Consider this Spring Boot bean: public class MyService { @PreDestroy public void cleanup() { System.out.println("Cleaning up resources"); } } Why might the cleanup method never be called when the application stops?

A The bean is not managed by Spring because it lacks a stereotype annotation like @Component.

B @PreDestroy methods only run on singleton beans, and this bean is prototype scoped.

C The application context is not closed properly, so @PreDestroy is skipped.

D The method is public and void, so it should run without issues.

💡 Hint

Check if Spring knows about this bean to manage its lifecycle.

If a class is not registered as a Spring bean (e.g., missing @Component), Spring does not manage its lifecycle, so @PreDestroy methods won't be called.

🧠 Conceptual

expert

What is the effect of multiple @PostConstruct methods in a single Spring bean?

If a Spring bean class has two methods both annotated with @PostConstruct, what will happen when the bean is initialized?

A Only the first declared @PostConstruct method will be called; the second is ignored.

B Both methods will be called in an undefined order during bean initialization.

C Spring will throw a runtime exception due to multiple @PostConstruct methods.

D Neither method will be called because of the conflict.

💡 Hint

Think about how Java handles multiple lifecycle callbacks in one class.

Spring calls all methods annotated with @PostConstruct in a bean, but the order is not guaranteed. Both methods will run during initialization.