Top Spring Boot Interview Questions and Answers: Beginner to Advanced Guide

If you’re preparing for a Spring Boot interview, you’re in the right place! Spring Boot is one of the most in-demand frameworks for Java developers, and understanding it well can give you a solid advantage in landing your dream job.

This article is your complete guide to Spring Boot interview questions, ranging from basic to advanced levels. We’ll break things down in an easy-to-understand tone, ensuring you feel confident when answering questions in an interview setting.

Let’s dive in!

---

1. What is Spring Boot, and why is it used?

Spring Boot is a framework that simplifies the creation of stand-alone, production-ready Spring-based applications. It is built on the Spring framework but removes much of the boilerplate configuration.

Key Reasons Why Spring Boot is Used:

• Reduces the need for manual configurations.
• Allows faster application development with minimal effort.
• Provides embedded servers like Tomcat or Jetty, so no need to deploy externally.
• It has features like auto-configuration and Spring Boot starters.

Example Interview Answer:

“Spring Boot is an extension of the Spring framework that focuses on reducing boilerplate code and making development easier. It uses auto-configuration and embedded servers to allow developers to quickly build and run applications.”

---

2. What are the key features of Spring Boot?

The most commonly discussed features of Spring Boot include:

1. Auto-Configuration: Automatically configures Spring beans based on dependencies.
2. Spring Boot Starters: Pre-defined templates to include dependencies easily (e.g., spring-boot-starter-web).
3. Embedded Servers: Built-in servers like Tomcat, Jetty, or Undertow.
4. Spring Boot Actuator: Provides production-ready endpoints to monitor and manage applications.
5. Spring Boot CLI: Allows running Spring Boot applications via command line.

How to Answer:

“The key features of Spring Boot include auto-configuration, embedded servers, Actuator for monitoring, and starters for dependency management. These features make it fast and efficient to develop production-ready Spring applications.”

---

3. What is the difference between Spring and Spring Boot?

Feature	Spring	Spring Boot
Configuration	Manual and XML-based configurations.	Auto-configuration with minimal setup.
Servers	External servers like Tomcat or Jetty.	Embedded servers (Tomcat, Jetty, etc.).
Dependency Management	Manual dependency handling.	Starter dependencies simplify it.
Project Setup	Time-consuming and complex.	Quick project setup with Spring Initializr.

Example Answer:

“Spring requires manual configurations, whereas Spring Boot provides auto-configuration and embedded servers. Spring Boot is designed to simplify the development process while using Spring under the hood.”

---

4. What is the Spring Boot Starter? Why is it useful?

A Spring Boot Starter is a set of pre-defined dependencies that help to reduce the burden of managing libraries.

For example:

• spring-boot-starter-web: Includes dependencies for building web applications (like Spring MVC and Tomcat).
• spring-boot-starter-test: Includes dependencies for testing (JUnit, Mockito, etc.).

Why is it Useful?

• Reduces the effort of managing individual dependencies.
• Makes it easy to include only what’s needed for the project.
• Avoids version conflicts in dependencies.

Answer Format:

“A Spring Boot Starter is a dependency template that groups commonly used libraries. For example, spring-boot-starter-web bundles everything needed for a web application. It simplifies dependency management.”

---

5. What is Spring Boot Auto-Configuration? How does it work?

Spring Boot’s auto-configuration automatically configures Spring beans based on project dependencies.

How it Works:

1. Spring Boot checks the classpath for required libraries.
2. Based on the available libraries, it configures default beans.
3. For example, if spring-web is present, Spring Boot auto-configures a DispatcherServlet.

Annotations Used:

• @SpringBootApplication: Includes @EnableAutoConfiguration and @ComponentScan.
• @ConditionalOnClass: Enables beans when specific classes exist.
• @ConditionalOnMissingBean: Defines a bean only if another bean is missing.

Example Answer:

“Spring Boot’s auto-configuration automatically configures Spring beans based on the libraries in the classpath. It uses annotations like @EnableAutoConfiguration to enable this behavior.”

---

6. What is the purpose of Spring Boot Actuator?

Spring Boot Actuator is a tool that helps monitor and manage your application in a production environment.

Key Features of Actuator:

• Health Endpoint: Check application health (/actuator/health).
• Metrics Endpoint: Get application performance data (/actuator/metrics).
• Info Endpoint: Display application information (/actuator/info).
• Custom Endpoints: Allows developers to create custom endpoints.

Answer Tip:

“Spring Boot Actuator provides production-ready features like health checks, metrics, and monitoring endpoints. It helps to monitor applications without writing extra code.”

---

7. How do you create a Spring Boot project?

You can create a Spring Boot project using three methods:

1. Spring Initializr (Recommended):
   • Go to https://start.spring.io/
   • Select project type (Maven/Gradle), dependencies, and Java version.
   • Download and unzip the generated project.
2. Spring Boot CLI:
   • Install Spring Boot CLI.
   • Run spring init --dependencies=web my-app to create a project.
3. Using IDE:
   • Use IntelliJ IDEA, Eclipse, or STS.
   • Create a new Spring Boot project and select required dependencies.

Example Answer:

“To create a Spring Boot project, I use Spring Initializr to generate the project structure with required dependencies. Then, I import it into my IDE and start building the application.”

---

8. What are some commonly used Spring Boot annotations?

Annotation	Purpose
@SpringBootApplication	Main annotation to enable Spring Boot features.
@RestController	Combines @Controller and @ResponseBody for REST APIs.
@RequestMapping	Maps HTTP requests to handler methods.
@Autowired	Injects a bean automatically.
@Value	Injects values from property files.
@Bean	Defines a Spring bean explicitly.
@EnableAutoConfiguration	Enables Spring Boot’s auto-configuration.

---

9. What is Spring Boot Dependency Injection?

Dependency Injection (DI) is a design pattern where Spring Boot manages the lifecycle of beans and injects dependencies automatically.

Types of Dependency Injection:

1. Constructor Injection: Injecting dependencies through a class constructor.
2. Setter Injection: Injecting dependencies via setter methods.
3. Field Injection: Using @Autowired to inject fields directly.

Example:

@Component
public class MyService {
    private final MyRepository repository;

    @Autowired
    public MyService(MyRepository repository) {
        this.repository = repository;
    }
}

10. How does Spring Boot handle exceptions?

Spring Boot provides a powerful exception-handling mechanism for REST APIs using @ControllerAdvice and @ExceptionHandler annotations.

Key Concepts:

1. Global Exception Handling: Use @ControllerAdvice to handle exceptions globally.
2. Custom Exception Handling: Use @ExceptionHandler for specific exceptions.
3. HTTP Status Codes: Return proper HTTP status codes with ResponseEntity.

Example:

@ControllerAdvice
public class GlobalExceptionHandler {
    @ExceptionHandler(ResourceNotFoundException.class)
    public ResponseEntity<String> handleNotFound(ResourceNotFoundException ex) {
        return new ResponseEntity<>(ex.getMessage(), HttpStatus.NOT_FOUND);
    }
}

---

Final Words

By thoroughly understanding these Spring Boot interview questions, you will be well-prepared to tackle technical interviews confidently. Practice explaining these concepts in simple terms, and use examples wherever possible.

Remember: Clarity, confidence, and examples are key to acing any Spring Boot interview.

Good luck with your preparation, and happy coding!