@Configuration and @Bean in Spring Boot - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to mark the class as a configuration class.

Spring Boot

@[1]
public class AppConfig {
}

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

AService

BComponent

CConfiguration

DRepository

Attempts:

3 left

💡 Hint

Common Mistakes

Using @Component instead of @Configuration

Forgetting the '@' symbol

Using unrelated annotations like @Service

The @Configuration annotation marks the class as a source of bean definitions for the Spring container.

2fill in blank

medium

Complete the code to define a bean method that returns a new instance of MyService.

Spring Boot

@Bean
public MyService [1]() {
    return new MyService();
}

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

AcreateService

BmyService

CserviceBean

DgetService

Attempts:

3 left

💡 Hint

Common Mistakes

Using invalid method names

Forgetting to add @Bean annotation

Returning null instead of new instance

The method name myService is used as the bean name by default.

3fill in blank

hard

Fix the error in the bean method declaration by completing the missing annotation.

Spring Boot

@[1]
public MyRepository [2]() {
    return new MyRepository();
}

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

A@Repository

B@Service

CmyRepository

D@Bean

Attempts:

3 left

💡 Hint

Common Mistakes

Using class-level annotations on methods

Omitting the @Bean annotation

Using @Component on methods instead of classes

The @Bean annotation is required on methods inside @Configuration classes to register beans. Also, the method needs a name.

4fill in blank

hard

Fill both blanks to complete the configuration class with a bean method.

Spring Boot

@[1]
public class ServiceConfig {
    @[2]
    public UserService userService() {
        return new UserService();
    }
}

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

AConfiguration

BComponent

CBean

DService

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up class and method annotations

Using @Component instead of @Configuration on class

Forgetting @Bean on method

The class must be annotated with @Configuration and the method with @Bean to define a bean.

5fill in blank

hard

Fill all three blanks to create a configuration class with two bean methods.

Spring Boot

@[1]
public class AppBeans {
    @[2]
    public ServiceA serviceA() {
        return new ServiceA();
    }

    @[3]
    public ServiceB serviceB() {
        return new ServiceB();
    }
}

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

AConfiguration

BBean

CComponent

DService

Attempts:

3 left

💡 Hint

Common Mistakes

Using @Component on class instead of @Configuration

Forgetting @Bean on one or both methods

Using @Service on methods

The class uses @Configuration, and each bean method uses @Bean to register beans.

Practice

1. What is the main purpose of the @Configuration annotation in Spring Boot?

easy

A. To enable automatic component scanning

B. To mark a method that returns a bean instance

C. To mark a class as a source of bean definitions for the application context

D. To configure database connections automatically

Solution

1. Step 1: Understand the role of @Configuration

   @Configuration tells Spring that this class contains methods to create beans.

2. Step 2: Differentiate from other annotations

   @Bean marks methods, not classes; component scanning is done by @ComponentScan; database config is separate.

3. Final Answer:

   To mark a class as a source of bean definitions for the application context -> Option C

4. Quick Check:

   @Configuration = class for beans [OK]

Hint: Remember: @Configuration is for classes, @Bean is for methods [OK]

Common Mistakes:

• Confusing @Configuration with @Bean
• Thinking @Configuration enables scanning
• Assuming it configures databases automatically

2. Which of the following is the correct way to define a bean method inside a @Configuration class?

easy

A. @Bean public MyBean myBean() { return new MyBean(); }

B. @Configuration public MyBean myBean() { return new MyBean(); }

C. public void createBean() { return new MyBean(); }

D. @Component public MyBean myBean() { return new MyBean(); }

Solution

1. Step 1: Check method signature for bean creation

   Bean methods must be annotated with @Bean and return the bean object.

2. Step 2: Verify syntax correctness

   @Bean public MyBean myBean() { return new MyBean(); } correctly uses @Bean and returns a new instance.

3. Final Answer:

   @Bean public MyBean myBean() { return new MyBean(); } -> Option A

4. Quick Check:

   @Bean + return bean instance = correct method [OK]

Hint: Bean methods need @Bean and must return the object [OK]

Common Mistakes:

• Missing @Bean annotation
• Using void return type
• Using @Configuration on methods

3. Given the following code, what will be the output when retrieving the bean named "service" from the Spring context?

@Configuration
public class AppConfig {
  @Bean
  public String service() {
    return "MyService";
  }
}

medium

A. "service"

B. "MyService"

C. An exception is thrown

D. null

Solution

1. Step 1: Identify the bean method and its return value

   The method named service returns the string "MyService" and is annotated with @Bean.

2. Step 2: Understand bean retrieval by name

   Spring registers this bean with the name "service" and returns the method's return value when requested.

3. Final Answer:

   "MyService" -> Option B

4. Quick Check:

   Bean name returns method's return value [OK]

Hint: Bean name matches method name; returns method's return value [OK]

Common Mistakes:

• Expecting bean name as output instead of return value
• Thinking Spring returns null if no explicit name
• Assuming exception without error in code

4. Identify the error in the following Spring configuration code:

@Configuration
public class Config {
  @Bean
  public void createBean() {
    // no return statement
  }
}

medium

A. Method must return an object, not void

B. Missing @Configuration annotation

C. Method name cannot be createBean

D. No error, code is correct

Solution

1. Step 1: Check method return type for @Bean

   Bean methods must return the bean object; void return type is invalid.

2. Step 2: Confirm annotations and method name

   @Configuration is present; method name can be anything; error is only return type.

3. Final Answer:

   Method must return an object, not void -> Option A

4. Quick Check:

   @Bean method needs return value, not void [OK]

Hint: Bean methods must return an object, never void [OK]

Common Mistakes:

• Using void return type for @Bean methods
• Confusing method name restrictions
• Missing @Configuration annotation (not in this case)

5. You want to create two beans of the same type but with different configurations using @Bean methods inside a @Configuration class. How can you ensure Spring distinguishes between them when injecting?

hard

A. Define both beans in separate @Configuration classes only

B. Use @Primary on both methods

C. Use the same method name but different return types

D. Use different method names for each @Bean method

Solution

1. Step 1: Understand bean naming in Spring

   By default, Spring uses the @Bean method name as the bean name to distinguish beans.

2. Step 2: Differentiate beans of same type

   Using different method names creates distinct bean names, allowing injection by name or qualifier.

3. Final Answer:

   Use different method names for each @Bean method -> Option D

4. Quick Check:

   Different method names = different bean names [OK]

Hint: Different method names create distinct bean names automatically [OK]

Common Mistakes:

• Using @Primary on both beans (conflicts)
• Same method name with different return types (not allowed)
• Thinking beans must be in separate classes