Bean lifecycle overview in Spring Boot - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a Spring bean using annotation.

Spring Boot

@Component
public class MyService {
    // Bean logic here
}

// The annotation [1] marks this class as a Spring bean.

Drag options to blanks, or click blank then click option'

A@Repository

B@Service

C@Component

D@Controller

Attempts:

3 left

💡 Hint

Common Mistakes

Using @Service or @Repository when the question asks for a generic bean annotation.

Forgetting to add any annotation.

The @Component annotation tells Spring to treat this class as a bean and manage its lifecycle.

2fill in blank

medium

Complete the code to implement a method that runs after bean initialization.

Spring Boot

public class MyBean implements InitializingBean {
    @Override
    public void [1]() throws Exception {
        System.out.println("Bean is initialized");
    }
}

Drag options to blanks, or click blank then click option'

AafterPropertiesSet

Bstart

Cinit

DpostConstruct

Attempts:

3 left

💡 Hint

Common Mistakes

Using @PostConstruct annotation method name instead of interface method.

Using a method name not defined in InitializingBean.

The afterPropertiesSet() method is called by Spring after the bean's properties are set, signaling initialization completion.

3fill in blank

hard

Fix the error in the bean destruction method name.

Spring Boot

public class MyBean implements DisposableBean {
    @Override
    public void [1]() throws Exception {
        System.out.println("Bean is being destroyed");
    }
}

Drag options to blanks, or click blank then click option'

Adestroy

Bdestroyed

Cdestroy()

DdestroyBean

Attempts:

3 left

💡 Hint

Common Mistakes

Adding parentheses in the method name placeholder.

Using incorrect method names like destroyBean or destroyed.

The correct method name in DisposableBean is destroy() without parentheses in the method signature placeholder.

4fill in blank

hard

Fill both blanks to define a bean with custom init and destroy methods.

Spring Boot

@Bean(initMethod = "[1]", destroyMethod = "[2]")
public MyBean myBean() {
    return new MyBean();
}

Drag options to blanks, or click blank then click option'

AcustomInit

BcustomDestroy

Cinit

Ddestroy

Attempts:

3 left

💡 Hint

Common Mistakes

Using default method names instead of custom ones.

Mixing up init and destroy method names.

The initMethod and destroyMethod specify custom methods to run during bean lifecycle events.

5fill in blank

hard

Fill all three blanks to create a bean with lifecycle annotations.

Spring Boot

public class MyBean {

    @[1]
    public void start() {
        System.out.println("Bean started");
    }

    @[2]
    public void stop() {
        System.out.println("Bean stopped");
    }

    @[3]
    public void cleanup() {
        System.out.println("Bean cleaned up");
    }
}

Drag options to blanks, or click blank then click option'

APostConstruct

BPreDestroy

CPreDestroyMethod

DPostDestroy

Attempts:

3 left

💡 Hint

Common Mistakes

Using non-existent annotations like @PreDestroyMethod or @PostDestroy.

Mixing up PostConstruct and PreDestroy.

The @PostConstruct annotation marks a method to run after bean creation. @PreDestroy marks a method before destruction. @PreDestroyMethod is incorrect; the correct annotation is @PreDestroy, so this is a trick option to test attention.

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