Bean concept in Spring in Spring Boot - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a Spring bean using annotation.

Spring Boot

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

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

AcreateService

BserviceBean

CmyService

DgetService

Attempts:

3 left

💡 Hint

Common Mistakes

Using method names that do not follow Java naming conventions.

Forgetting to annotate the method with @Bean.

The method name myService is used as the bean name by default in Spring when using @Bean.

2fill in blank

medium

Complete the code to inject a bean into a Spring component using annotation.

Spring Boot

@Component
public class UserController {
    private final UserService userService;

    public UserController([1] UserService userService) {
        this.userService = userService;
    }
}

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

A@Autowired

B@Inject

C@Qualifier

D@Resource

Attempts:

3 left

💡 Hint

Common Mistakes

Using @Qualifier without specifying a bean name.

Forgetting to annotate the constructor parameter.

The @Autowired annotation tells Spring to inject the bean automatically into the constructor.

3fill in blank

hard

Fix the error in the bean scope declaration.

Spring Boot

@Bean
@Scope([1])
public SessionBean sessionBean() {
    return new SessionBean();
}

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

A"prototype"

B"session"

C"singleton"

D"request"

Attempts:

3 left

💡 Hint

Common Mistakes

Using "singleton" scope for session-specific beans.

Forgetting to import the correct Scope annotation.

The "session" scope defines a bean that is created once per HTTP session in Spring web applications.

4fill in blank

hard

Fill both blanks to create a bean with a custom name and prototype scope.

Spring Boot

@Bean(name = "[1]")
@Scope("[2]")
public ProductService [3]() {
    return new ProductService();
}

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

AcustomProductService

Bsingleton

Cprototype

DproductService

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up the bean name and method name.

Using singleton scope instead of prototype.

The bean is named customProductService, has prototype scope, and the method name is productService.

5fill in blank

hard

Fill all three blanks to define a bean with lazy initialization, singleton scope, and a qualifier.

Spring Boot

@Bean
@Lazy([1])
@Scope("[2]")
@Qualifier("[3]")
public NotificationService notificationService() {
    return new NotificationService();
}

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

Atrue

Bfalse

Csingleton

DemailService

Attempts:

3 left

💡 Hint

Common Mistakes

Setting lazy to false when lazy initialization is desired.

Using incorrect qualifier names.

The bean is lazily initialized (true), has singleton scope, and is qualified with emailService.

Practice

1. What is a Bean in the Spring framework?

easy

A. A type of Java exception

B. A database connection

C. An object managed by the Spring container

D. A user interface component

Solution

1. Step 1: Understand Spring's role

   Spring manages objects to help organize and connect parts of an application.

2. Step 2: Define what a Bean is

   A Bean is any object that Spring creates and manages in its container.

3. Final Answer:

   An object managed by the Spring container -> Option C

4. Quick Check:

   Bean = Managed object [OK]

Hint: Beans are Spring-managed objects, not UI or exceptions [OK]

Common Mistakes:

• Confusing beans with database connections
• Thinking beans are UI elements
• Assuming beans are exceptions

2. Which annotation is used to declare a class as a Spring Bean?

easy

A. @Qualifier

B. @Component

C. @Autowired

D. @RequestMapping

Solution

1. Step 1: Identify annotations for beans

   @Component marks a class as a Spring-managed bean.

2. Step 2: Differentiate from other annotations

   @Qualifier specifies which bean to inject, @Autowired injects beans, @RequestMapping maps web requests.

3. Final Answer:

   @Component -> Option B

4. Quick Check:

   @Component = Bean declaration [OK]

Hint: Use @Component to declare beans; others serve different roles [OK]

Common Mistakes:

• Confusing @Autowired with bean declaration
• Using @RequestMapping for beans
• Thinking @Qualifier declares beans

3. Given the code below, what will be printed (assuming the @Autowired field and System.out.println are inside a Spring-managed class)?

@Component
public class MyBean {
  public String greet() { return "Hello Spring"; }
}

@Autowired
MyBean myBean;

System.out.println(myBean.greet());

medium

A. Hello Spring

B. null

C. Compilation error

D. No output

Solution

1. Step 1: Understand @Component and @Autowired

   @Component creates the bean, @Autowired injects it into the field.

2. Step 2: Check method call output

   Calling greet() returns "Hello Spring", so it prints that string.

3. Final Answer:

   Hello Spring -> Option A

4. Quick Check:

   Injected bean method returns greeting [OK]

Hint: Autowired injects bean; method returns greeting string [OK]

Common Mistakes:

• Assuming null because of missing initialization
• Thinking it causes compile error
• Expecting no output without System.out.println

4. What is wrong with this Spring bean declaration?

@Component
public class MyService {
  @Autowired
  private MyRepository repo;

  public void doWork() {
    repo.save();
  }
}

Assuming MyRepository is not annotated as a bean.

medium

A. No @Autowired on MyService class

B. Missing @Service annotation on MyService

C. Method doWork() should return a value

D. MyRepository is not a Spring bean, so injection fails

Solution

1. Step 1: Check bean injection requirements

   Spring can only inject beans that are managed by the container.

2. Step 2: Identify missing bean annotation

   MyRepository lacks @Component or similar, so Spring cannot inject it.

3. Final Answer:

   MyRepository is not a Spring bean, so injection fails -> Option D

4. Quick Check:

   Injection requires bean annotation [OK]

Hint: Injected classes must be beans too [OK]

Common Mistakes:

• Thinking @Service is mandatory for injection
• Assuming method must return value
• Confusing @Autowired placement

5. You want to create a bean that returns a customized object. Which method correctly defines a bean using Java configuration?

hard

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

B. @Component
public MyBean myBean() {
return new MyBean("custom");
}

C. public MyBean myBean() {
return new MyBean("custom");
}

D. @Autowired
public MyBean myBean() {
return new MyBean("custom");
}

Solution

1. Step 1: Understand @Bean usage

   @Bean annotation on a method inside a @Configuration class defines a bean returned by that method.

2. Step 2: Differentiate from other annotations

   @Component is for classes, not methods; @Autowired injects dependencies, not defines beans.

3. Final Answer:

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

4. Quick Check:

   @Bean method returns custom bean [OK]

Hint: Use @Bean on methods inside @Configuration classes [OK]

Common Mistakes:

• Using @Component on methods instead of classes
• Omitting @Bean annotation
• Confusing @Autowired with bean creation