Bean lifecycle overview in Spring Boot - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a Spring Bean?

A Spring Bean is an object that is managed by the Spring IoC container. It is created, configured, and managed by Spring during the application runtime.

beginner

Name the main phases of the Spring Bean lifecycle.

The main phases are: Instantiation, Property Population (Dependency Injection), Initialization, Usage, and Destruction.

intermediate

What happens during the Initialization phase of a Spring Bean?

During Initialization, Spring calls any custom initialization methods or lifecycle callbacks like @PostConstruct or afterPropertiesSet() to prepare the bean for use.

intermediate

How can you customize the destruction of a Spring Bean?

You can customize destruction by implementing DisposableBean interface, using @PreDestroy annotation, or specifying a destroy-method in the bean configuration.

beginner

What role does the Spring IoC container play in the Bean lifecycle?

The Spring IoC container controls the entire lifecycle of beans: creating, wiring dependencies, initializing, and destroying them when no longer needed.

Which annotation is used to run code after a Spring Bean has been initialized?

A @PostConstruct

B @PreDestroy

C @Autowired

D @Bean

@PostConstruct runs after the bean is fully initialized.

What is the first step in the Spring Bean lifecycle?

A Initialization

B Destruction

C Instantiation

D Dependency Injection

Instantiation is when the bean object is created.

Which interface can a Spring Bean implement to customize its destruction logic?

A InitializingBean

B DisposableBean

C BeanFactory

D ApplicationContext

DisposableBean interface allows custom destruction code.

When does Spring perform dependency injection on a bean?

A During property population phase

B After destruction

C Before instantiation

D After usage

Dependency injection happens during property population.

Which annotation marks a method to be called before a bean is destroyed?

A @PostConstruct

B @Component

C @Autowired

D @PreDestroy

@PreDestroy marks methods to run before bean destruction.

Explain the full lifecycle of a Spring Bean from creation to destruction.

Think about how Spring manages the bean step by step.

How can you add custom behavior during the initialization and destruction phases of a Spring Bean?

Consider both annotations and interfaces.

Practice

1. Which of the following best describes the lifecycle of a Spring bean?

easy

A. Creation, initialization, use, and destruction

B. Compilation, execution, and garbage collection

C. Declaration, inheritance, and polymorphism

D. Loading, linking, and running

Solution

1. Step 1: Understand Spring bean lifecycle phases

   Spring beans go through creation, initialization, usage, and destruction phases during their lifecycle.

2. Step 2: Compare options with lifecycle phases

   Only Creation, initialization, use, and destruction correctly lists these phases. Other options describe unrelated programming concepts.

3. Final Answer:

   Creation, initialization, use, and destruction -> Option A

4. Quick Check:

   Bean lifecycle = Creation, init, use, destroy [OK]

Hint: Remember bean lifecycle phases: create, init, use, destroy [OK]

Common Mistakes:

• Confusing bean lifecycle with Java program lifecycle
• Mixing bean lifecycle with object-oriented concepts
• Thinking lifecycle only involves creation and destruction

2. Which annotation is used in Spring to run a method after a bean's properties have been set?

easy

A. @PostConstruct

B. @PreDestroy

C. @Autowired

D. @Bean

Solution

1. Step 1: Identify annotation for post-initialization

   @PostConstruct is the annotation used to mark a method to run after bean properties are set.

2. Step 2: Eliminate other annotations

   @PreDestroy runs before destruction, @Autowired injects dependencies, and @Bean defines a bean method.

3. Final Answer:

   @PostConstruct -> Option A

4. Quick Check:

   @PostConstruct runs after properties set [OK]

Hint: PostConstruct runs after init, PreDestroy before destroy [OK]

Common Mistakes:

• Confusing @PreDestroy with @PostConstruct
• Using @Autowired for lifecycle methods
• Thinking @Bean runs after initialization

3. Given this Spring bean code snippet, what will be printed when the bean is initialized?

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

medium

A. Bean destroyed

B. No output

C. Bean initialized

D. Compilation error

Solution

1. Step 1: Understand @PostConstruct behavior

   The method annotated with @PostConstruct runs after the bean is created and properties set, printing "Bean initialized".

2. Step 2: Check output possibilities

   Since the method prints a message on init, output will be "Bean initialized". No errors or destruction messages occur here.

3. Final Answer:

   Bean initialized -> Option C

4. Quick Check:

   @PostConstruct prints "Bean initialized" [OK]

Hint: PostConstruct method runs once after bean creation [OK]

Common Mistakes:

• Expecting output on bean destruction instead
• Thinking no output occurs without explicit call
• Confusing syntax causing compilation errors

4. What is wrong with this Spring bean code if the cleanup() method is never called?

@Component
public class MyBean {
  public void cleanup() {
    System.out.println("Cleaning up");
  }
}

medium

A. cleanup method should be static

B. Missing @PreDestroy annotation on cleanup method

C. Missing @PostConstruct annotation on cleanup method

D. cleanup method must return a value

Solution

1. Step 1: Identify lifecycle annotation for destruction

   The cleanup method should be annotated with @PreDestroy to run before bean destruction.

2. Step 2: Check other options for correctness

   @PostConstruct is for initialization, static or return value are not required for lifecycle methods.

3. Final Answer:

   Missing @PreDestroy annotation on cleanup method -> Option B

4. Quick Check:

   @PreDestroy needed to run cleanup before destroy [OK]

Hint: Use @PreDestroy to run code before bean destruction [OK]

Common Mistakes:

• Using @PostConstruct instead of @PreDestroy for cleanup
• Making cleanup static unnecessarily
• Expecting cleanup to run without annotation

5. You want to ensure a Spring bean runs a method both after initialization and before destruction. Which combination correctly achieves this?

hard

A. Implement InitializingBean interface only

B. Annotate the same method with both @PostConstruct and @PreDestroy

C. Use @Autowired on init method and @PreDestroy on destroy method

D. Annotate one method with @PostConstruct and another with @PreDestroy

Solution

1. Step 1: Understand lifecycle annotations usage

   @PostConstruct runs after initialization, @PreDestroy runs before destruction; they must be on separate methods.

2. Step 2: Evaluate other options

   Annotating the same method with both annotations is invalid. @Autowired is for injection, not lifecycle. Implementing InitializingBean interface only handles post-initialization but not destruction.

3. Final Answer:

   Annotate one method with @PostConstruct and another with @PreDestroy -> Option D

4. Quick Check:

   Separate methods with @PostConstruct and @PreDestroy [OK]

Hint: Use separate methods for init (@PostConstruct) and destroy (@PreDestroy) [OK]

Common Mistakes:

• Trying to use one method for both init and destroy
• Confusing @Autowired with lifecycle annotations
• Using InitializingBean interface only