Spring Boot Interview Questions and Answers

Introduction

Spring Boot is really popular for building applications that are safe and work well. It handles a wide range of operations automatically.  It has its own servers, which makes it easier to develop things. So people who make software and companies all over the world like to use Spring Boot. Now that more people are using Spring Boot, companies want to hire people who really know how Spring Boot works and can use it in their work. This list of Spring Boot Interview Questions and Answers is meant to help freshers with Spring Boot and professionals who already know a lot about it, so they can understand it better, get ready for job interviews, and have a chance of getting a job as a Java developer. Start your learning journey with our detailed Spring Boot Course Syllabus.

Spring Boot Interview Questions for Freshers

1. What is Spring Boot, and how does it compare to the Spring Framework?

Spring Boot is a way to make Java application development faster and easier. It is an extension of the Spring Framework. Spring Boot reduces the amount of configuration that developers need to do. It helps developers build production applications with minimal setup.

Difference Between Spring Framework and Spring Boot

• Spring Framework
  • Requires configuration
  • Needs an external server
  • More setup required
  • More code needed
• Spring Boot
  • Uses auto-configuration
  • Comes with embedded servers
  • Quick and easy setup
  • Less code required

2. Could you describe the important features of Spring Boot?

Spring Boot offers several features that simplify application development. These features include:

• Auto-Configuration – This automatically configures application settings.
• Starter Dependencies – These are made dependency packages.
• Embedded Servers – Include Tomcat, Jetty, or Undertow.
• Spring Boot Actuator – Helps monitor and manage applications.
• Rapid Development – This speeds up project creation and deployment.

3. What are Spring Boot Starters?

Spring Boot Starters are -configured dependency packages. They simplify project setup. Instead of adding multiple libraries individually, developers can add a single starter dependency.

Common Starters

• spring-boot-starter-web – For web and REST API development.
• spring-boot-starter-data-jpa – For database operations using JPA and Hibernate.
• spring-boot-starter-security – For application security.
• spring-boot-starter-test – For testing applications.

Starters save time. Ensure dependency compatibility.

4. What is Auto-Configuration, and how do you disable a specific class?

Auto-Configuration is a feature that automatically configures Spring components based on the libraries available in the project. For example, if a database driver is present, Spring Boot automatically creates a database connection.

To disable an auto-configuration class, use the exclude attribute:

• @SpringBootApplication(exclude = {DataSourceAutoConfiguration.class})

This prevents Spring Boot from loading the configuration.

5. What does the @SpringBootApplication annotation do internally?

@SpringBootApplication is commonly used to mark Spring Boot applications. It combines three annotations:

• @Configuration – Marks the class as a configuration class for defining beans.
• @EnableAutoConfiguration – This enables configuration.
• @ComponentScan – This scans and detects Spring components

Using this single annotation simplifies application setup.

6. What are Embedded Servers and why are they beneficial?

Embedded servers are web servers packaged directly inside the application. 

• Spring Boot supports:
  • Tomcat
  • Jetty
  • Undertow
• Benefits:
  • No need to install a server.
  • Easy deployment using a JAR file.
  • Faster development and testing.
  • Simplified application management.
• Applications can run using:
  • java -jar application.jar

7. What is Spring Initializr?

Spring Initializr is a web-based tool. It helps developers quickly create Spring Boot projects. 

• With Spring Initializr, you can:
  • Choose a Java version.
  • Select Maven or Gradle.
  • Add dependencies.
  • Download a to-use project structure.
  • It saves time and simplifies project creation.

8. Explain the difference between @Controller and @RestController.

Both annotations handle web requests. They serve different purposes.

• @Controller
  • Used in web applications.
  • Returns HTML. Views.
  • Works with JSP, Thymeleaf, and other view technologies.
• @RestController
  • Used for web services.
  • Returns JSON or XML data directly.
  • Combines @Controller and @ResponseBody.

@RestController is commonly used for API development.

9. What is Dependency Injection, and how does Spring implement it?

Dependency Injection is a design pattern. It is where objects receive their dependencies from a source rather than creating them manually. Spring uses its IoC container to manage dependencies

• Common Types of Dependency Injection
  • Constructor Injection
    • Dependencies are passed through the constructor.
    • Recommended approach.
    • Improves code maintainability.
  • Setter Injection
    • Dependencies are provided through setter methods.
    • Useful for optional dependencies.

Spring commonly uses the @Autowired annotation to inject dependencies.

10. Differentiate between @Component, @Service, and @Repository.

These annotations register classes as Spring-managed beans. They indicate roles.

• @Component
  • Generic annotation for any Spring bean.
  • Used when no specific role exists.
• @Service
  • Used for business logic classes.
  • Improves code readability and organization.
• @Repository
  • Used for data access layers.
  • Handles database operations.
  • Provides exception translation.

Learn with our easy and beginner-friendly Spring Boot tutorials.

11. What is Spring Boot Actuator?

Spring Boot Actuator provides production monitoring and management features. Common Actuator Endpoints

• /actuator/health – Checks application health.
• /actuator/metrics – Displays performance metrics.
• /actuator/env – Shows environment properties.
• /actuator/info – Displays application information.

An actuator helps developers monitor applications efficiently.

12. How do you configure a database connection in Spring Boot?

Database configuration is usually done in the application.properties file.

• spring.datasource.url=jdbc:mysql://localhost:3306/your_database
• spring.datasource.username=root
• spring.datasource.password=your_password
• spring.jpa.hibernate.ddl-auto=update

Spring Boot handles database connection setup automatically if the necessary driver is present.

13. What are Spring Boot Profiles and why are they used?

Spring Boot Profiles allow developers to use configurations for different environments.

• Common environments include:
  • Development (dev)
  • Testing (test)
  • Production (prod)
• Example:
  • spring.profiles.active=prod
• Benefits
  • Environment-specific settings.
  • Better configuration management.
  • Easier deployment across environments.

14. What is the difference between @RequestMapping and @GetMapping?

Both annotations map HTTP requests to controller methods.

• @RequestMapping
  • Supports all HTTP methods.
  • Can be used at class and method levels.
  • Provides flexible request mapping.
• @GetMapping
  • Specifically handles GET requests.
  • Simplifies code readability.
• Acts as a shortcut for:
  • @RequestMapping(method = RequestMethod.GET)

15. What are Spring Boot DevTools?

Spring Boot DevTools is a development utility. It improves developer productivity. Key Features

• Automatic Restart – Restarts the application when code changes.
• LiveReload Support – Automatically refreshes the browser.
• Disabled Caching – Reflects changes immediately.
• Faster Development Cycle – Reduces manual restarts.

DevTools is mainly used during development and is not recommended for production environments.

Spring Boot Interview Questions for Experienced Candidates

1. Explain the internal lifecycle of the Spring Boot startup process.

When you run a Spring Boot application, it starts with SpringApplication.run().

Spring Boot follows these steps:

• Loads initializers and listeners.
• Prepares the application environment.
• Creates the ApplicationContext.
• Performs component scanning and bean creation.
• Starts the embedded server (Tomcat, Jetty, etc.).
• Executes CommandLineRunner and ApplicationRunner classes.

This helps Spring Boot start applications automatically with configuration.

2. What causes a CircularDependencyException, and how do you resolve it at production scale?

A CircularDependencyException happens when two beans depend on each other during initialization.

• Solutions:
  • Refactor the code. Move shared logic to another service.
  • Use the @Lazy annotation to delay bean loading.
  • Redesign the application architecture to avoid dependency cycles.

Refactoring is the approach for production applications.

3. Why is Field Injection strongly discouraged, and what should you use instead?

Field Injection can make code hard to test and maintain.

• Problems with Field Injection:
  • It makes dependencies less visible.
  • It prevents immutability.
  • It increases testing complexity.
• Recommended Solution:
  • Use Constructor Injection instead because it:
    • Improves code readability.
    • Supports objects.
    • Makes unit testing easier.

4. Why does a @Transactional annotation sometimes fail to roll back or execute?

The @Transactional annotation may not work correctly in certain situations.

• Common reasons are:
  • Self-invocation within the class.
  • The method is private or protected.
  • Checked exceptions require explicit configuration to trigger a rollback.
• To fix it:
  • Keep methods public.
  • Use rollbackFor = Exception.class when needed.
  • Call transactional methods through Spring-managed beans.

5. How do you resolve a LazyInitializationException in Spring Data JPA?

LazyInitializationException happens when loaded data is accessed after the database session is closed.

• Best practices are:
  • Use JOIN FETCH in JPQL queries.
  • Use @EntityGraph for entities.
  • Return DTOs of entities when appropriate.

Do not enable spring.jpa.open-in-view=true in production.

6. Why is spring.jpa.hibernate.ddl-auto=update strictly forbidden in Production environments?

Using ddl-auto=update can automatically modify database tables during application startup.

• The risks are:
  • Accidental schema changes.
  • Data loss or table issues.
  • Lack of version control.
• Recommended Approach:
  • Use validate or none.
  • Manage database changes with Flyway or Liquibase.

7. What is the architectural difference between application.properties and bootstrap.properties?

Both files store configuration settings. They are loaded at different stages.

• bootstrap.properties:
  • Loaded first.
  • Used with Spring Cloud Config.
  • Handles external configurations.
• application.properties:
  • Loaded later.
  • Stores application-specific settings.
  • Commonly used for database and server configurations.

8. How do you handle and propagate errors globally across Microservices?

Spring Boot provides centralized exception handling using @RestControllerAdvice.

The benefits are:

• Consistent error responses.
• Better API design.
• Easier maintenance.

Use methods to manage custom exceptions across the application.

9. How do you construct custom metrics using Spring Boot Actuator?

Spring Boot uses Micrometer to create business metrics.

• The steps are:
  • Inject MeterRegistry.
  • Create Counters, Gauges, or Timers.
  • Record application events and statistics.

These metrics can be monitored using Prometheus and Grafana dashboards.

10. How does Spring Boot manage and optimize database connection pooling?

Spring Boot uses HikariCP as the default connection pool.

Important properties are:

• maximum-pool-size – Maximum database connections.
• minimum-idle – Minimum idle connections.
• connection-timeout – Wait time for a connection.

Proper tuning improves application performance and scalability.

11. What are the key strategies to optimize a slow Spring Boot application startup?

Large applications can experience startup times.

• Optimization techniques are:
  • Enable initialization.
  • Exclude auto-configurations.
  • Limit component scanning.
  • Use Spring AOT and GraalVM Native Images.

These techniques help significantly reduce startup time.

12. How do you implement robust, stateless security for Microservices?

Modern microservices usually use JWT or OAuth2 for server-side sessions.

• Best practices are:
  • Use Spring Security.
  • Configure JWT authentication.
  • Set session policy to STATELESS.
  • Validate tokens using custom filters.

This improves security and scalability.

13. How do you resolve a Circular Dependency exception in Spring Boot?

A circular dependency occurs when two beans depend on each other.

• Common solutions are:
  • Refactor the design.
  • Introduce a service layer.
  • Use @Lazy when necessary.
  • Consider setter injection in cases.

Refactoring remains the solution.

14. How do you scale and optimize Spring Boot performance for high throughput?

For high-traffic applications, performance optimization is essential.

• Recommended techniques are:
  • Tune HikariCP connection pools.
  • Use Redis or Caffeine caching.
  • Implement processing with @Async.
  • Use pagination for loading large datasets.

These practices improve application speed and resource usage.

15. How do you implement secure authorization in a microservices ecosystem?

Authorization ensures that users can access permitted resources.

• Security best practices are:
  • Use OAuth2 and JWT tokens.
  • Validate requests through an API Gateway.
  • Apply role-based access control using @PreAuthorize.
  • Secure service-to-service communication.

This approach provides secure authorization across microservices.

Get hands-on experience by working on real-time Spring Boot projects.

Conclusion

In conclusion, Spring Boot is still a popular choice for building modern Java applications. Looking at these Spring Boot Interview Questions and Answers can help you get the main ideas, solve problems, and prepare for technical interviews. If you are just starting or have been working with Spring Boot for a while, doing it regularly and getting hands-on experience will help you do well in your job. Spring Boot is a tool to have in your toolkit, and knowing it well can really help you succeed. Receive expert career support from our trusted Training and Placement Institute in Chennai.