@Configuration and @Bean in Spring Boot - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the output of this Spring Boot configuration?

Given the following Spring Boot configuration class, what will be printed when the application context is started and the messageService bean is used to print the message?

Spring Boot

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
public class AppConfig {
    @Bean
    public String messageService() {
        return "Hello from @Bean!";
    }
}

// In main application or test:
// System.out.println(context.getBean("messageService"));

A Hello from @Bean!

B null

C Compilation error due to missing @ComponentScan

D Runtime error: NoSuchBeanDefinitionException

💡 Hint

Remember that @Bean methods define beans in the Spring context and return the object to be managed.

The @Bean annotated method returns a String bean with the value "Hello from @Bean!". When retrieved from the context, it prints exactly that string.

📝 Syntax

intermediate

Which option correctly defines a @Bean method in a @Configuration class?

Select the option that correctly defines a Spring bean method inside a @Configuration class.

Spring Boot

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
public class MyConfig {
    // Choose the correct method below
}

A

@Bean
public String greeting() {
    return "Hi!";
}

B

@Bean
public String greeting(String name) {
    return "Hi " + name;
}

C

@Bean
public void greeting() {
    System.out.println("Hi!");
}

D

public String greeting() {
    return "Hi!";
}

💡 Hint

A @Bean method must return an object to be managed by Spring and have no parameters unless they are other beans.

Option A correctly defines a @Bean method returning a String. Option A lacks @Bean annotation. Option A returns void which is invalid for a bean. Option A has a parameter without Spring knowing how to inject it.

🔧 Debug

advanced

Why does this @Bean method cause a runtime error?

Consider this @Configuration class: @Configuration public class Config { @Bean public Integer number() { return Integer.parseInt("abc"); } } What happens when the Spring context starts?

Spring Boot

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
public class Config {
    @Bean
    public Integer number() {
        return Integer.parseInt("abc");
    }
}

A Bean 'number' is created with value 0

B Bean 'number' is created with null value

C Application context fails to start with NumberFormatException

D Compilation error due to invalid parse

💡 Hint

Parsing "abc" as an integer is invalid and throws an exception.

Integer.parseInt("abc") throws NumberFormatException at runtime, causing the Spring context startup to fail.

🧠 Conceptual

advanced

What is the role of @Configuration in Spring Boot?

Choose the best description of what @Configuration does in a Spring Boot application.

A @Configuration is used to inject dependencies into beans

B @Configuration marks a class as a source of bean definitions for the application context

C @Configuration automatically scans all packages for components

D @Configuration replaces the need for @Component annotations

💡 Hint

Think about what Spring does with classes annotated with @Configuration.

@Configuration tells Spring that the class contains methods annotated with @Bean that define beans to be managed in the context.

❓ state_output

expert

What is the value of the bean 'counter' after context initialization?

Given this configuration class: @Configuration public class CounterConfig { private int count = 0; @Bean public Integer counter() { return ++count; } @Bean public Integer anotherCounter() { return ++count; } } What is the value of the bean named 'counter' when retrieved from the context?

Spring Boot

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
public class CounterConfig {
    private int count = 0;

    @Bean
    public Integer counter() {
        return ++count;
    }

    @Bean
    public Integer anotherCounter() {
        return ++count;
    }
}

A Throws an exception due to bean initialization order

B 2

C 0

D 1

💡 Hint

Each @Bean method is called once during context initialization in some order.

Spring calls each @Bean method once. The first call to counter() increments count from 0 to 1 and returns 1. The second call to anotherCounter() increments count to 2. The bean 'counter' has value 1.