Navratri Sale: Get Upto 30% OFF on Live Training! Offer Ending in
D
H
M
S
Get Now
Top 50 Spring Boot Interview Questions and Answer

Top 50 Spring Boot Interview Questions and Answer

28 Aug 2024
Beginner
301 Views
33 min read

Spring Boot Interview Question With Answer

Spring Boot is an open-source framework for building standalone, production-ready Spring applications. It provides a quick approach to creating microservices and web applications using the Spring Framework, avoiding the need for significant standard code.

In this Java Tutorial, I'll cover the top 50 Spring Boot interview questions and answers, separated into three categories: 20 for beginners, 15 for intermediate developers, and 15 for experienced experts. This article will help you fully prepare for any Spring Boot interviews you may have.

Top 20 Spring Boot Interview Questions and Answers For Beginners

1. What is Spring Boot?

Spring Boot is developed on top of the Spring framework to create stand-alone RESTful web applications with minimal configuration. The application does not require external servers to function because it has embedded servers such as Tomcat and Jetty.

  • The Spring Boot framework operates independently.
  • It creates production-ready spring apps.

2. What are the Features of Spring Boot?

Spring Boot includes several important features. A few of them are listed below:

  • Auto-configuration: Spring Boot automatically configures dependencies using the @EnableAutoconfiguration annotation, reducing boilerplate code.
  • Spring Boot Starter POM: These POMs provide pre-configured dependencies for functions such as database, security, and Maven setup.
  • Spring Boot CLI (Command Line Interface): This command line tool is mostly used for managing dependencies, creating projects, and running apps.
  • Actuator: The Spring Boot Actuator performs health checks, collects metrics, and monitors application endpoints. It also facilitates troubleshooting management.
  • Embedded Servers: Spring Boot has embedded servers such as Tomcat and Jetty that allow applications to execute quickly. There is no need for external servers.

Q3. Explain the concept of Spring Boot Starters.

Spring Boot Starters are pre-configured sets of dependencies that make it simple to include the necessary libraries for various functionalities, including web development, security, and JPA.

Example:


<dependency>
    org.springframework.boot
    spring-boot-starter-web
</dependency>

Q4. What is the purpose of the @SpringBootApplication annotation?

@SpringBootApplication represents a shortcut for three annotations: @Configuration, @EnableAutoConfiguration, and @ComponentScan. It initializes the application context and enables auto-configuration.

Q5. What are the advantages of using Spring Boot?

Spring Boot is a framework for building standalone, production-grade Spring-based applications, offering many advantages.

  • Easy to use: Spring Boot reduces the amount of boilerplate code required to construct a Spring application.
  • Rapid Development: Spring Boot's opinionated approach and auto-configuration allow developers to create apps quickly without the need for time-consuming setup, reducing development time.
  • Scalable: Spring Boot applications are designed to be scalable. This means that they may be easily scaled up or down to meet your application's requirements.
  • Production-ready: Spring Boot contains capabilities such as metrics, health checks, and externalized configuration, all of which are intended for usage in production situations.

Q6. Define the Key Components of Spring Boot.

The key components of Spring Boot are given below:

  • Spring Boot Starters
  • Auto-configuration
  • Spring Boot Actuator
  • Spring Boot CLI for Embedded Servers

Q7. How does Spring Boot handle dependencies?

Spring Boot manages dependencies with the Maven or Gradle build tools. It includes a set of default dependencies that may be modified, allowing developers to select the most relevant versions and libraries for their applications.

FeatureDefault Dependency
Web Developmentspring-boot-starter-web
Data Accessspring-boot-starter-data-jpa
Securityspring-boot-starter-security

Q8 Why do we prefer Spring Boot over Spring?

Here's a table that outlines why we prefer Spring Boot over Spring Framework.
AspectSpring BootSpring Framework
Setup and ConfigurationSpring Boot automatically configures your project, making setup simpler and faster.Manual configuration is required, which might take a long and be complex.
Development SpeedAllows faster development with less boilerplate code.Development is slower because more setup is needed.
Dependency ManagementManages dependencies automatically, simplifying project setup.Dependencies need to be managed manually, which can be complicated.
Embedded ServerIt includes an embedded server that allows you to run applications directly.Requires an external server setup to deploy applications.
MicroservicesDesigned for microservices, making them easy to create and deploy.It can be used for microservices but requires more configuration.
Production-Ready FeaturesIt includes features like metrics and health checks that are out of the box.Does not include these features by default; they need to be added manually.
Community& EcosystemHas a large community with frequent updates and extensive resources.Also has a strong community, but it evolves more slowly compared to Spring Boot.

Q9 What is Spring Initializr?

A web application called Spring Initializr helps you establish a new Spring Boot project easily by choosing dependencies, configuring project metadata, and producing a project structure that is ready for use.

Q10 How do you create a Spring Boot project using Spring Initializer?

Detailed steps for creating a project using Spring Boot.
  • Step 1: Open Spring Initializr by going to https://start.spring.io.
  • Step 2:Specify Project Details: To produce and download a Spring Boot project, input all the required information and click the Produce Project button. Then, open the downloaded zip file and drag it into your favorite integrated development environment.
  • Step 3: After that, import the file into Eclipse.
In Eclipse, choose File -> Import -> Existing Maven Project. Navigate to or enter the location of the folder where you extracted the zip file on the following page. After you click Finish, Maven will need some time to download all the dependencies and start the project.

Q11 What are the Spring Boot Starter Dependencies?

Spring Boot includes multiple starter dependencies. The following are some of the most commonly utilized in the Spring Boot application:
  • Data JPA starter
  • Web starter
  • Security starter
  • Test Starterz
  • Thymeleaf starter

Q12 How does a spring application get started?

  • A Spring application is launched by invoking the main() method of the SpringApplication class, which has the @SpringBootApplication annotation.
  • This function accepts a SpringApplicationBuilder object as an argument and is used to configure the application.
  • Once the SpringApplication object is constructed, the run() function is invoked.
  • After initializing the application context, the run() method launches the program's embedded web server.

Example

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class MySpringApplication {

    public static void main(String[] args) {
        SpringApplication.run(MySpringApplication.class, args);
    }
}

Q13 Explain the concept of auto-configuration in Spring Boot.

  • The application context is automatically configured via auto-configuration using the dependencies found in the classpath.
  • As a result, less manual configuration is required, which facilitates getting started.

Q14 How do you disable a specific auto-configuration class?

To disable a certain auto-configuration class in a Spring Boot application, use the @EnableAutoConfiguration annotation and the "exclude" attribute.

Example

spring.autoconfigure.exclude=org.springframework.boot.autoconfigure.jdbc.DataSourceAutoConfiguration

Q14 What is the starter dependency of the Spring boot module?

Spring Boot Starters are a set of pre-configured Maven dependencies that make it easy to create specific types of apps. These starters include:
  • Dependencies
  • Version Control
  • Certain features require configuration to function properly.
To use a Spring Boot startup dependency, simply add it to your project's pom.xml file. For example, to include the Spring Boot starting web dependency, add the following dependent to the pom.xml file:

Example

<dependency>
    org.springframework.boot
    spring-boot-starter-web
</dependency>

Q15 How do you create a Spring Boot project using boot CLI?

  • Setting up the CLI: Use SDKMAN to install the Spring Boot CLI (Command-Line Interface) directly!
  • Employing the CLI: Once installed, run the CLI by typing spring and pressing Enter.
  • Launch a New Project: Using start.spring.io and the init command, you can launch a new project without leaving the shell.
  • Using the Embedded Shell: Spring Boot includes command-line completion techniques for the BASH and ZSH shells.

Q16 How does Spring Boot handle security?

  • Spring Boot interfaces with Spring Security to handle authentication and authorization.
  • It has default setups that can be changed with annotations and security configuration classes.

Example

@Configuration
@EnableWebSecurity
public class SecurityConfig extends WebSecurityConfigurerAdapter {
    @Override
    protected void configure(HttpSecurity http) throws Exception {
        http
            .authorizeRequests()
            .antMatchers("/public").permitAll()
            .anyRequest().authenticated()
            .and()
            .formLogin().permitAll();
    }
}

Q17 How do you create a custom banner in Spring Boot?

  • To build a custom startup banner, place a banner.txt file in the src/main/resources directory.
  • Inside banner.txt, you can add any text, ASCII art, or messages you want to display when the application starts.
  • Run the application, and your custom Spring Boot banner will appear in the console.Q18 What is the use of @ConfigurationProperties in Spring Boot?

@ConfigurationProperties maps properties from application.properties or application.yml to Java objects. This provides organized access to your application's configuration properties.

Example

@ConfigurationProperties(prefix = "app")
public class AppConfig {
    private String name;
    private String description;
    // getters and setters
}

Q19 How does Spring Boot handle external configuration?

  • Spring Boot supports a variety of external configuration options.
  • It supports property files (application.properties or application.yml) that can be stored in a variety of locations, including the classpath, file system, and external directories.
  • Spring Boot also allows environment variables, command-line arguments, and the creation of profiles for various deployment contexts.
  • The configuration values can be obtained using the @Value annotation or bound to Java objects using the @ConfigurationProperties annotation.

Q20 How do you handle exceptions in Spring Boot?

  • The @ControllerAdvice and @ExceptionHandler annotations in Spring Boot allow exceptions to be handled globally.
  • This enables the logic for addressing errors throughout the program to be centralized.

Example

@ControllerAdvice
public class GlobalExceptionHandler {
    @ExceptionHandler(Exception.class)
    public ResponseEntity handleException(Exception e) {
        return new ResponseEntity<>(e.getMessage(), HttpStatus.INTERNAL_SERVER_ERROR);
    }
}

Top 15 Spring Boot Interview Questions and Answers For Intermediates

Q21 What is Tomcat's default port in spring boot?

The default port for Spring Boot's embedded Tomcat server is 8080. We can alter the default port by modifying the server. A port attribute in your application's application.properties file.

Q22 Can we disable the default web server in the Spring Boot application?

Yes, we can turn off the default web server in the Spring Boot application. To accomplish this, change the server. Port property in the application.properties file to "-1".

Q23 Explain the flow of HTTPS requests through the Spring Boot application.

HTTPS requests pass through a Spring Boot application.
The flow of HTTPS requests through a Spring Boot application is as follows:
  • The client initiates an HTTP request (GET, POST, PUT, DELETE) to the browser.
  • Following that, the request is routed to the controller, where it is mapped and handled along with all other requests.
  • Following this, all business logic will be executed in the Service layer. It performs business logic on data that has been mapped to JPA (Java Persistence API) via model classes.
  • The repository layer handles all CRUD activities for the REST APIs.
  • If there are no errors, the end users receive a JSP page.

Q24 Explain @RestController annotation in Spring Boot.

The @RestController annotation is essentially a shortcut for creating RESTful services. It combines two annotations.

  • @Controller: Indicates that the class is a request handler in the Spring MVC framework.
  • @ResponseBody: This tells Spring to convert method return values (objects, data) directly into HTTP responses rather than rendering views.

It allows us to define endpoints for multiple HTTP methods (GET, POST, PUT, and DELETE), return data in various forms (e.g., JSON, XML), and map request parameters to method arguments.

Q25 How do you implement RESTful web services in Spring Boot?

Spring Boot allows you to construct RESTful web services using the @RestController and @RequestMapping annotations. The @RestController annotation automatically serializes return objects to JSON or XML, making it simple to build REST APIs.

Example

@RestController
@RequestMapping("/api")
public class MyRestController {
    @GetMapping("/items")
    public List getItems() {
        return itemService.getAllItems();
    }
}

Q26 What is the difference between @RequestMapping and @GetMapping in Spring Boot?

AnnotationPurpose
@RequestMappingAnnotation that can be used for handling HTTP requests of all methods, including GET and POST.
@GetMappingA specialized version of @RequestMapping is used to handle GET requests.

Q27 How do you integrate Spring Boot with a database?

Spring Boot interfaces with databases via Spring Data JPA, simplifying the data access layer. The program often provides configuration information. Property files and repositories are built by extending the JpaRepository.

Example

@Repository
public interface UserRepository extends JpaRepository<User, Long> {
}

Example application.properties:

spring.datasource.url=jdbc:mysql://localhost:3306/mydb
spring.datasource.username=root
spring.datasource.password=password

Q28 What is the purpose of @Entity in Spring Boot?

The @Entity annotation defines a JPA entity, which is a lightweight, persistent domain object that represents a table in a database. It is commonly used alongside @Id, @GeneratedValue, and other JPA annotations.

Example

@Entity
public class User {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String name;
    private String email;

    // getters and setters
}

Q29 How do you implement pagination in Spring Boot?

Spring Boot pagination can be accomplished using Spring Data JPA's Pageable interface. It enables data retrieval in pieces, which improves performance when working with huge datasets.

Example

@Repository
public interface UserRepository extends JpaRepository {
    Page findAll(Pageable pageable);
}

Example usage:

Pageable pageable = PageRequest.of(0, 10);
Page users = userRepository.findAll(pageable);

Q30 What is the purpose of @Transactional in Spring Boot?

The @Transactional annotation manages transactions in Spring Boot applications. Developers can create transactional boundaries to ensure data consistency and rollback in the event of an error.

Example

@Service
public class UserService {
    @Transactional
    public void createUser(User user) {
        userRepository.save(user);
    }
}

Q31 Difference between @Controller and @RestController.

FeaturesIt is used to mark a class as a controller.It is a combination of @Controller and @ResponseBody.
ApplicationIt is used for web applications.It is used for RESTful APIs.
Request handling & mapping.It is used with @RequestMapping to map HTTP requests to methods.It is used to handle requests like GET, PUT, POST, and DELETE.

Q32 What are the differences between @SpringBootApplication and @EnableAutoConfiguration annotation?

Features@SpringBootApplication@EnableAutoConfiguration
When to UseIt is used when we want to use auto-configuration.It is used when we want to customize auto-configuration.
Entry PointIt is typically used on the main class of a Spring Boot application, serving as the entry point.It can be used on any configuration class or with @SpringBootApplication.
Component ScanningIt includes @ComponentScan annotation to enable component scanning.It does not perform component scanning by itself.
Example
@SpringBootApplication
public class MyApplication {
    public static void main(String[] args) {
        SpringApplication.run(MyApplication.class, args);
    }
}
@Configuration
@EnableAutoConfiguration
public class MyConfiguration { }

Q33 What are Profiles in Spring?

Spring Profiles are similar to different scenarios for an application based on its surroundings.
  • You create sets of configurations (such as database URLs) for various scenarios (development, testing, production).
  • Use the @Profile annotation to specify which configuration belongs where.
  • Activate profiles using environment variables or command-line parameters.

To use Spring Profiles, simply define the spring.profiles.active property and select which profile to use.

Q34 What are the differences between WAR and embedded containers?

FeatureWAREmbedded Containers
PackagingIt contains all the files needed to deploy a web application to a web server.It is a web application server included in the same JAR file as the application code.
ConfigurationIt requires external configuration files (e.g., web.xml, context.xml) to define the web application.It uses configuration properties or annotations within the application code.
SecurityIt can be deployed to a web server that is configured with security features.It can be made more secure by using security features provided by JRE.

Q35 Spring Vs. Spring Boot?

  • Spring is a framework that includes a variety of modules for developing enterprise-level applications.
  • Spring Boot is a framework that makes Spring development easier by offering a pre-configured environment in which developers may focus on developing application logic.

Top 15 Spring Boot Interview Questions and Answers For Experienced.

Q36 What are the best practices for building a production-grade Spring Boot application?

Best practices include creating profiles for environment-specific setups, putting in place security measures, optimizing performance, and establishing monitoring and logging.
PracticeDescription
ProfilesIt is used to manage different settings for development, testing, and production environments.
SecurityIt involves implementing HTTPS, OAuth2, and JWT to ensure secure communication.
MonitoringIt is done using Actuator, Prometheus, and Grafana to monitor application health and performance effectively.
Performance OptimizationIt is achieved by fine-tuning database connections, caching strategies, and memory usage to enhance application performance.

Q37 How do you implement microservices using Spring Boot? 

Spring Cloud, which includes tools for service discovery, load balancing, circuit breakers, and distributed tracing, can be used to construct microservices. Each service has its own Spring Boot program.

Example

@SpringBootApplication
public class MyMicroserviceApplication {
    public static void main(String[] args) {
        SpringApplication.run(MyMicroserviceApplication.class, args);
    }
}

Q38 What is Spring Cloud Config, and how is it used in Spring Boot? 

Spring Cloud Config supports externalized configuration on both the server and the client sides of a distributed system. It enables Spring Boot applications to retrieve configuration properties from a common store.

Example Configuration


spring.cloud.config.uri=http://localhost:8888

Q39 How do you optimize the performance of a Spring Boot application? 

Performance optimization includes fine-tuning database connections, caching, shortening startup time, and reducing memory use. To monitor performance data, employ tools such as Spring Boot Actuator and JMX.
Optimization AreaTechniques
Database ConnectionsIt is done by using connection pooling and lazy loading.
CachingIt is implemented using @Cacheable and Redis.
Startup TimeIt is improved by using a spring-context-indexer to reduce startup time.
Memory UsageIt is optimized by adjusting JVM settings and bean scopes.

Q40 What is dependency injection, and what are its types?

Dependency Injection (DI) is a design pattern that lets us create loosely linked components. In DI, an object's capacity to execute a job is dependent on another object. There are three forms of dependence injections.
  • Constructor injection is the most used method of DI in Spring Boot, and constructor injection involves injecting the dependent object into the dependent object's constructor.
  • Setter injection involves injecting the dependent object into the dependent object's setter method.
  • Field injection involves injecting the dependent object into the dependent object's field.

Q41 What is the difference between Constructor and Setter Injection?

FeaturesConstructor InjectionSetter Injection
DependencyIt is provided through constructor parameters.It is set through setter methods after object creation.
ImmutabilityIt promotes immutability as dependencies are set at creation.It allows dependencies to be changed dynamically after object creation.
Dependency OverridingIt is harder to override dependencies with different implementations.It allows easier overriding of dependencies using different setter values.

Q42 What is the role of Spring Cloud Gateway in a Spring Boot microservices architecture? 

Spring Cloud Gateway is a simple and efficient approach to route requests to various microservices. It provides load balancing, path rewriting, and security while also serving as an API gateway.

Example


@SpringBootApplication
public class GatewayApplication {
    public static void main(String[] args) {
        SpringApplication.run(GatewayApplication.class, args);
    }
}

Example Configuration


spring:
  cloud:
    gateway:
      routes:
        - id: myService
          uri: http://localhost:8081
          predicates:
            - Path=/service/**

Q43 How do you handle versioning in a Spring Boot application? 

Versioning can be accomplished using URI versioning, request parameter versioning, or header versioning.

Example


@RestController
@RequestMapping("/api/v1")
public class MyController {
    @GetMapping("/users")
    public List getUsersV1() {
        // Version 1 implementation
    }
}

@RestController
@RequestMapping("/api/v2")
public class MyControllerV2 {
    @GetMapping("/users")
    public List getUsersV2() {
        // Version 2 implementation
    }
}

Q44 What differentiates Spring Data JPA and Hibernate? 

  • Hibernate, a Java Persistence API (JPA) implementation, enables Object-Relational Mapping (ORM) by allowing users to store, retrieve, map, and change application data across Java objects and relational databases. 
  • Hibernate converts Java data types to SQL (Structured Query Language) data types and Java classes to database tables, allowing developers to avoid scripting data persistence in SQL applications. 
  •  Spring Data JPA, a Spring Data sub-project, provides abstraction over the DAL (Data Access Layer) by combining JPA and Object-Relational Mapping implementations like Hibernate. 
  • Spring Data JPA makes it easier to construct JPA repositories and aims to improve DAL implementation significantly. 

Q45 How do you secure RESTful web services in Spring Boot? 

Spring Security can be used to secure RESTful web services by leveraging OAuth2, JWT tokens, and role-based access control.

Example

@Configuration
@EnableWebSecurity
public class SecurityConfig extends WebSecurityConfigurerAdapter {
    @Override
    protected void configure(HttpSecurity http) throws Exception {
        http
            .authorizeRequests()
            .antMatchers("/api/public").permitAll()
            .anyRequest().authenticated()
            .and()
            .oauth2Login();
    }
}

Q46 How do you handle transactions in Spring Boot? 

  • Spring Boot manages transactions with the @Transactional annotation. 
  • This annotation ensures that database actions within a method are carried out within a transaction. 
  • If an operation fails, all changes are reversed to ensure data consistency. 
  • Advanced transaction management allows you to configure propagation behavior, isolation level, and rollback rules.

Example

@Service
public class AccountService {

    @Transactional
    public void transferMoney(Long fromAccountId, Long toAccountId, BigDecimal amount) {
        // Perform debit from source account
        // Perform credit to destination account
    }
}

Q47 How can you optimize the performance of a Spring Boot application? 

Spring Boot performance optimization uses a variety of methods, including caching, connection pooling, and query optimization. Using @Cacheable annotations, allowing connection pooling (e.g., HikariCP), and optimizing database queries with correct indexing and pagination can all help to enhance application speed. 

Q48 What is Spring Boot's DevTools, and how does it enhance development productivity? 

Spring Boot DevTools is a module that boosts developer productivity by enabling automatic application restart, live reloading, and configurable property overrides. This enables developers to observe changes in real-time without manually restarting the application, which speeds up the development process. 

Q49 How do you externalize configuration in Spring Boot, and why is it important? 

Spring Boot externalizes configuration via properties files, YAML files, environment variables, or command-line arguments. Externalizing configuration increases the application's flexibility, allowing it to be quickly modified without requiring code modifications when switching between contexts such as development, staging, and production.

Example

# application.yml
server:
  port: 8080

spring:
  datasource:
    url: jdbc:mysql://localhost:3306/mydb
    username: user
    password: pass

Q50 What are the different ways to test Spring Boot applications?

  • Spring Boot apps can be tested using a variety of approaches: Unit testing focuses on testing individual components, such as services or repositories, utilizing frameworks such as JUnit and Mockit. 
  • This ensures that each component of the program works independently. Integration testing determines how various components of an application interact with one another. 
  • Spring Boot supports the @SpringBootTest annotation, which loads the entire application context for testing. 
  • Slice testing focuses on specific layers of the application (such as the web, service, and data layers). 
  • To test only the necessary parts of the application, use annotations such as @WebMvcTest, @DataJpaTest, and @RestClientTest. End-to-End Testing: Ensures that the entire application works as expected, which is commonly accomplished with automated UI testing tools such as Selenium or Cucumber.
Summary
This article includes a comprehensive list of the top 50 Spring Boot interview questions organized by experience level. It has 20 questions for beginners, 15 for intermediate developers, and 15 for seasoned pros. The questions cover key Spring Boot concepts such as configuration, transactions, security, and performance, with actual code examples and clear explanations to help with interview preparation. To build your career in Java, consider our Full-Stack Java Developer Certification Training Course.

FAQs

Q1. How do you explain Spring Boot project in an interview?

If asked, explain that Spring Boot is an open-source, Java-based Spring framework that's commonly used to create standalone applications that don't rely on an external web server

Q2. Is Spring Boot in demand?

There is a lot of demand for Spring Boot professionals due to several reasons: Simplicity and Productivity: Spring Boot simplifies the development process of Spring-based applications by providing opinionated defaults and auto-configuration.

Q3. How do I prepare for a Spring Boot interview?

To prepare for a Spring Boot interview, focus on understanding the core concepts, such as dependency injection, Spring Boot annotations, and application configuration. Practice building RESTful APIs, integrating databases using Spring Data JPA, and handling security with Spring Security. Be ready to discuss the Spring Boot ecosystem, including microservices, and review common design patterns and best practices. Lastly, hands-on coding practice and revisiting key concepts will help reinforce your knowledge. 
Share Article
About Author
Shailendra Chauhan (Microsoft MVP, Founder & CEO at Scholarhat by DotNetTricks)

Shailendra Chauhan is the Founder and CEO at ScholarHat by DotNetTricks which is a brand when it comes to e-Learning. He provides training and consultation over an array of technologies like Cloud, .NET, Angular, React, Node, Microservices, Containers and Mobile Apps development. He has been awarded Microsoft MVP 9th time in a row (2016-2024). He has changed many lives with his writings and unique training programs. He has a number of most sought-after books to his name which has helped job aspirants in cracking tough interviews with ease.
Self-paced Membership
  • 24+ Video Courses
  • 825+ Hands-On Labs
  • 400+ Quick Notes
  • 125+ Skill Tests
  • 10+ Interview Q&A Courses
  • 10+ Real-world Projects
  • Career Coaching Sessions
  • Email Support
Upto 60% OFF
Know More
Accept cookies & close this