Top 70 Spring Boot Interview Questions

Spring Boot is a powerful framework that makes developing Spring applications easier and faster. As a developer, you can create Spring Boot by following many configuration steps required to set up a general Spring application. 

To show your skills and expertise on the Top Spring Boot topics in big organisations, you need to prepare well for Top Spring Boot interview questions from scratch. We have listed down 70 Spring Boot Interview questions into different categories to make your preparation smoother.

Questions based on Spring Boot

Find 10 questions and answers related to the Introduction in Spring Boot Interview Questions:

Question 1: What is Spring Boot? Answer: Spring Boot is a framework that simplifies the development of Java applications by providing pre-configured setups and reducing the need for boilerplate code.

Question 2: How do you create a Spring Boot application? Answer: Create a Spring Boot application using Spring Initializr, which generates a project with the necessary dependencies and structure.

Question 3: What is the purpose of the ´@SpringBootApplication´ annotation? Answer: The ´@SpringBootApplication´ annotation marks the main class of a Spring Boot application. It combines three annotations: ´@EnableAutoConfiguration´, ´@ComponentScan´, and ´@Configuration´.

Question 4: How does Spring Boot manage dependencies? Answer: Spring Boot uses Maven or Gradle for dependency management. It provides starters, which are sets of convenient dependency descriptors you can include in your project.

Question 5: What is the use of the ´application.properties´ file? Answer: The ´application.properties´ file is used to configure various settings for your Spring Boot application, such as server port, database connection, and logging levels.

Question 6: How do you change the default port of a Spring Boot application? Answer: Change the default port by adding the following line to your ´application.properties´ file:

Question 7: What is the purpose of Spring Boot starters? Answer: Spring Boot starters are pre-defined dependency packages that simplify the inclusion of related dependencies. For example, ´spring-boot-starter-web´ includes all necessary dependencies for a web application.

Question 8: How do you run a Spring Boot application? Answer: You can run a Spring Boot application by executing the ´main´ method of your main class (annotated with ´@SpringBootApplication´). Alternatively, you can use the ´mvn spring-boot:run´ or ´gradle bootRun´ command.

Question 9: What is Spring Boot Actuator? Answer: Spring Boot Actuator provides production-ready features such as monitoring and management through endpoints. It helps you understand and manage your application in real-time.

Question 10: How do you handle exceptions in a Spring Boot application? Answer: Handle exceptions in a Spring Boot application using the ´@ControllerAdvice´ and ´@ExceptionHandler´ annotations. These allow you to create global exception handlers for your application.

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Core Concept Questions

Find 10 questions and answers related to Core Concepts Questions in Spring Boot Interview Questions:

Question 1: What is auto-configuration in Spring Boot? Answer: Auto-configuration in Spring Boot automatically configures your Spring application based on the dependencies you have added. It tries to guess the best configuration for your needs.  For example, if you include the `spring-boot-starter-web` dependency, Spring Boot will automatically set up a web server and other necessary components like a dispatcher servlet, view resolver, etc., without needing much manual configuration.

Question 2: How do you create a RESTful web service using Spring Boot? Answer: To create a RESTful web service in Spring Boot: 1. Create a Spring Boot project: Use Spring Initializr (start.spring.io) to generate a new project with the `spring-boot-starter-web` dependency. 2. Define a Controller: Create a class annotated with `@RestController` to handle HTTP requests. 3. Map endpoints: Use `@GetMapping`, `@PostMapping`, etc., to map HTTP methods to specific methods in your controller. “`java @RestController @RequestMapping(“/api”)public class MyController {         @GetMapping(“/greet”)     public String greet() {         return “Hello, World!”;     } } “`

Question 3: What is Spring Boot DevTools? Answer: Spring Boot DevTools is a module that helps with the development process. It provides features like automatic restarts, live reload, and configurations that are only useful during development.  When you change a file, DevTools will automatically restart the application, so you don’t have to do it manually.

Question 4: How do you connect a Spring Boot application to a database? Answer: To connect a Spring Boot application to a database: 1. Add dependencies: Include `spring-boot-starter-data-jpa` and the appropriate database driver in your `pom.xml`. 2. Configure the database: Add database connection details (URL, username, password) in `application.properties` or `application.yml`. 3. Create a JPA entity: Define a class annotated with `@Entity` representing a table in the database. 4. Create a repository: Define an interface that extends `JpaRepository`. Example of configuration in `application.properties`: “`properties spring.datasource.url=jdbc:mysql://localhost:3306/mydb spring.datasource.username=root spring.datasource.password=rootpassword spring.jpa.hibernate.ddl-auto=update“`

Question 5: What is Spring Data JPA in Spring Boot? Answer: Spring Data JPA is a part of Spring Data, which makes it easier to implement JPA-based repositories.  It reduces the boilerplate code required for data access and provides powerful methods to interact with the database. By extending `JpaRepository`, you get CRUD operations and the ability to define custom queries.

Question 6: How do you secure a Spring Boot application? Answer: To secure a Spring Boot application: 1. Add security dependency: Include `spring-boot-starter-security` in your project. 2. Configure security: Create a class that extends `WebSecurityConfigurerAdapter` and override its methods to define security rules. Example: “`java @Configuration @EnableWebSecurity public class SecurityConfig extends WebSecurityConfigurerAdapter {         @Override     protected void configure(HttpSecurity http) throws Exception{         http             .authorizeRequests()             .antMatchers(“/public/**”).permitAll()             .anyRequest().authenticated()            .and()             .formLogin()             .loginPage(“/login”).permitAll()             .and()             .logout().permitAll();     } } “`

Question 7. What is the difference between ´@Component´, ´@Service´, and ´@Repository´ in Spring Boot? Answer. Here is the difference between ´@Component´, ´@Service´, and ´@Repository´ in Spring Boot. ´@Component`: A generic stereotype for any Spring-managed component. It’s a general-purpose annotation. `@Service`: A specialization of `@Component`, it indicates that the class contains business logic. `@Repository`: Also a specialization of `@Component`, it indicates that the class is responsible for data access and might catch database exceptions and translate them into Spring’s DataAccessException.

Question 8: How does Spring Boot handle externalized configuration? Answer: Spring Boot handles externalized configuration by allowing you to define settings in `application.properties` or `application.yml`. These files can reside in different locations and be overridden by environment variables, command-line arguments, or other property sources. Example `application.properties`: “`properties server.port=8081 spring.datasource.url=jdbc:mysql://localhost:3306/mydb“`

Question 9: What is the purpose of the ´@SpringBootTest´ annotation? Answer: `@SpringBootTest` is used in testing to indicate that the application context should be loaded for the test. It provides a comprehensive test environment that mimics the real application context, allowing you to write integration tests that verify the behavior of your application.

Question 10. How do you enable scheduling in a Spring Boot application? Answer. To enable scheduling in a Spring Boot application: 1. Enable scheduling: Add `@EnableScheduling` to a configuration class. 2. Create a scheduled task: Use `@Scheduled` on methods that should run periodically. Example: “`java @Configuration @EnableScheduling public class SchedulingConfig { } @Component public class MyScheduledTask {         @Scheduled(fixedRate = 5000)     public void performTask() {         System.out.println(“Task executed at ” + new Date());     }} “` This setup will execute `performTask` every 5 seconds.

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Question on Spring Boot Starters

Find 10 questions and answers related to Question on Spring Boot Starters in Spring Boot Interview Questions:

Question 1: What are Spring Boot Starters? Answer: Spring Boot Starters are a set of convenient dependency descriptors that you can include in your project to get a ready-to-use set of libraries for common tasks, like building web applications or accessing databases.

Question 2: Why should you use Spring Boot Starters? Answer: You should use Spring Boot Starters to save time and reduce the hassle of manually specifying and configuring dependencies. They provide a quick and easy way to set up common functionalities.

Question 3: What is the ´spring-boot-starter-web´ starter used for? Answer: The ´spring-boot-starter-web´ starter is used to build web applications. It includes dependencies for Spring MVC, RESTful services, and embedded servers like Tomcat.

Question 4: How do you add a Spring Boot Starter to your project? Answer: You add a Spring Boot Starter to your project by including it in your pom.xml (for Maven) or build.gradle (for Gradle) file. For example, to add spring-boot-starter-web using Maven:

Question 5: What is the ´spring-boot-starter-data-jpa´ starter? Answer: The ´spring-boot-starter-data-jpa´ starter is used to include Spring Data JPA, Hibernate, and other necessary libraries to work with relational databases using JPA (Java Persistence API).

Question 6: What does the ´spring-boot-starter-test´ starter provide? Answer: The ´spring-boot-starter-test´ starter provides dependencies for testing Spring Boot applications, including JUnit, Hamcrest, and Mockito. It makes it easier to write and run tests.

Question 7: How do Spring Boot Starters simplify dependency management? Answer. Spring Boot Starters simplify dependency management by grouping commonly used dependencies into a single starter package, reducing the need to specify each dependency individually.

Question 8: What is the ´spring-boot-starter-security´ starter? Answer: The ´spring-boot-starter-security´ starter is used to add Spring Security to your project. It provides security features such as authentication, authorization, and protection against common attacks.

Question 9: Can you create your own custom Spring Boot Starter? Answer: Yes, you can create your own custom Spring Boot Starter by defining a new module with a ´pom.xml´ or ´build.gradle´ file that includes the desired dependencies and configurations. This custom starter can then be reused across multiple projects.

Question 10: What is the spring-boot-starter-actuator starter used for? Answer: The ´spring-boot-starter-actuator´ starter is used to add production-ready features to your application, such as monitoring, metrics, and health checks. It provides endpoints to help manage and monitor your application in real time.

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Spring Boot Configuration Question

Find 10 questions and answers related to Spring Boot Configuration Question in Spring Boot Interview Questions:

Question 1: What is the purpose of the ´application.properties´ file in Spring Boot? Answer: The ´application.properties´ file is used to configure various settings in a Spring Boot application, such as server port, database connection details, and custom application properties.

Question 2: How do you change the server port in a Spring Boot application? Answer: You change the server port by adding the following line to the ´application.properties´ file:

Question 3: What is the difference between ´application.properties´ and ´application.yml´? Answer: ´Application.properties´ and ´application.yml´ are used for configuration in Spring Boot. The difference lies in their format: ´application.properties´ uses key-value pairs, while ´application.yml´ uses YAML syntax, which can be more readable and supports hierarchical data.

Question 4: How do you configure a Spring Boot application to connect to a MySQL database? Answer: Add the MySQL driver dependency to ´pom.xml´ and configure the data source in ´application.properties´.

Question 5: How can you set up an embedded server (like Tomcat) in a Spring Boot application? Answer: Spring Boot uses an embedded server by default. Form Tomcat, simply include the ´spring-boot-starter-web´ dependency in your ´pom.xml´

Question 6: How do you externalize configuration in a Spring Boot application? Answer: You can externalize configuration using ´application.properties´ or ´application.yml´ files, environment variables, command-line argument, or Spring Cloud Config for centralized configuration.

Question 7: How do you profile-specific properties in Spring Boot? Answer: Define profile-specific properties files like ´application-dev.properties´ and ´application-prod.properties.´ Activate a profile by setting the ´spring.profiles.active´ property:

Question 8: How do you enable scheduling in a Spring Boot application? Answer: To schedule in the Spring application add the ´@EnableScheduling´ annotation to a configuration class and use ´@Scheduled´ on the methods you want to run scheduled tasks.

Question 9: How do you configure logging in a Spring Boot application? Answer: Configure logging in ´application.properties´ or ´logback-spring.xml´. Let us see an example in ´application properties´:

Question 10: How do you configure a custom banner in Spring Boot? Answer: Create a ´banner.txt´ file in the ´src/main/resources´directory with the custom ASCII art or text you want to display on application startup.

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Spring Boot Actuator

Find 10 questions and answers related to Spring Boot Actuator in Spring Boot Interview Questions:

Question 1: What is Spring Boot Actuator? Answer: Spring Boot Actuator provides production-ready features to help you monitor and manage your Spring Boot application. It includes endpoints for health checks, metrics, and more.

Question 2: How do you enable Spring Boot Actuator in a project? Answer: Add the ´spring-boot-starter-actuator´dependency to your ´pom.xml’:

Question 3: How do you access Actuator endpoints? Answer: By default, Actuator endpoints are accessible via HTTP at ´/actuator´. For example, ´https://localhost:8080/actuator/health´for for health checks.

Question 4: How can you customize the Actuator endpoints? Answer: Customize Actuator endpoints using the ´application.properties´ file. For example, to enable the ´shutdown´endpoint:

Question 5: What is the purpose of the ´/actuator/health´endpoints? Answer: The ´/actuator/health/´endpoint provides the health status of your application. It checks various components and reports whether they are operating correctly.

Question 6: What is the purpose of the ´/actuator health/´endpoints? Answer: The ´/actuator/health/´endpoints provide the health status of your application. It checks various components and reports whether they are operating correctly.

Question 7: How do you secure Actuator endpoints? Answer: Secure Actuator endpoints using Spring Security. You can configure security settings in a class that extends ´WebSecurityConfigureAdapter´:

Question 8: How do you add custom health indicators? Answer: Implement the ´HeathIndicator´ interface and override the ´health´ method. Register the custom health indicator as a Spring bean:

Question 9: What is the ´/actuator/info´endpoint used for? Answer: The ´/actuator/info´endpoint provides general information about the application. You can customize the information by adding properties to ´application.properties´:

Question 10: How do you configure custom metrics in Spring Boot Actuator? Answer: Use the ¨MeterRegistry´ to create custom metrics. For example

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Security in Spring Boot

Find 10 questions and answers related to Security in Spring Boot Interview Questions:

Question 1: What is Spring Security in Spring Boot? Answer: Spring Security is a framework in Spring Boot that provides authentication, authorization, and other security features for your application. It helps you secure your web application by configuring security measures easily.

Question 2: How do you add Spring Security to a Spring Boot application? Answer: To add Spring Security to a Spring Boot application, you need to include the ´spring-boot–starter-security dependency in your ´pom.xml.´file. Spring Boot will automatically configure basic security settings.

Question 3: How do you create a custom login page in Spring Security? Answer: To create a custom login page, you configure it in your security configuration class by overriding the ´configure (HttpSecurity http)´method. Use the ´formLogin ()´ method and set your login page URL with ´loginPage(¨/my-login-page¨)´.

Question 4: What is CSRF and how do you enable it in Spring Boot? Answer: CSRF (Cross-Site Request Forgery) is an attack that tricks a user performing actions they did not intend to. Spring Security enables CSRF protection by default. You cna disable it (not recommended) by configuring ´http.csrf (). Disable ()´ in your security configuration class.

Question 5: How do you secure REST endpoints in a Spring Boot application? Answer: To secure REST endpoints, you can configure HTTP security in your security configuration class. Use ´authorizeRequests()´ to specify which endpoints need authentication and authorization, and use ´httpBasic ()´ or ´forLogin ()´ for authentication mechanisms.

Question 6: What is the purpose of the ´@Secured´ annotation in Spring Security? Answer: The ´@Secured´ annotation is used to specify security constraints on individual methods. You can use it to allow access to a method only to users with certain roles for example, ´@Secured(¨ROLE_USER¨)´.

Question 7: How do you store use details for authentication in Spring Security? Answer: You can store user details in memory, in a database, or using an external authentication provider. For in-memory storage, use ´InMemoryUserDetailsManager´ and for database storage, you typically implement ´UserDetailsService´ and configure a ¨JdbcUserDetailsManage´.

Question 8: What is the difference between ´@PreAuthorize´ and ´annotation? Answer: The ´@PreAuthorize´ annotation checks the given expression before the method executes, ensuring that the user has the necessary permissions. The ´@PostAuthrize´ annotation checks the expression after the method has executed, which can be useful for checking the return values.

Question 9: How do you implement password encoding in Spring Security? Answer: To implement password encoding, you configure a ´PasswordEncoder´ bean. Commonly used encoders include ´BCryptPasswordEncoder´. You use this encoder to hash passwords before storing them and to verify passwords during login.

Question 10: What is OAuth2 and how does Spring Boot support it? Answer: OAuth2 is an authorization framework that allows applications to access resources on behalf of users. Spring Boot supports OAuth2 by providing auto-configuration for OAuth2 resources and clients. You can configure OAuth2 properties in your application properties file and use the ´spring-security-oauth2-client´ dependency for integration.

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Deployment and Monitoring

Find 10 questions and answers related to Deployment and Monitoring Spring Boot Interview Questions:

Question 1: How do you package a Spring Boot application for deployment? Answer: You package a Spring Boot application as a JAR (Java ARchive) or WAR (Web Application Archive) file. You can do this by running ´mvn package´ for Maven or ´ ./gradlew build´ for Gradle, which creates the packaged file in the ´target´ or ´build/libs´ directory.

Question 2: How do you run a Spring Boot application as a standalone JAR? Answer: You run a Spring Boot application as a standalone JAR by using the command ´java -jar your-application.jar´. This starts the embedded web server and runs your application.

Question 3: How do you deploy a Spring Boot application to a server like Tomcat? Answer: To deploy a Spring Boot application to a Tomcat server, you package it as a WAR file by setting ´packaging´ to ´war´ in your pom.xml. Then, you copy the WAR file to the ´webapps´ directory of your Tomcat server.

Question 4: How do you configure environment-specific properties in Spring Boot? Answer: You configure environment-specific properties by creating separate properties files for each environment, such as ´application-dev.properties´ and ´application-prod.properties´. You then specify the active profile using ´spring.profiles.active´ in your application properties or as a command-line argument.

Question 5: How do you use Docker to deploy a Spring Boot application? Answer: You deploy a Spring Boot application using Docker by creating a ´Dockerfile´ that specifies the base image, copies your JAR file into the image, and sets the command to run the JAR. You then build the Docker image with ´docker build´ and run it with ´docker run´.

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Monitoring Questions

Question 6: What is Spring Boot Actuator and how does it help in monitoring? Answer: Spring Boot Actuator provides production-ready features like health checks, metrics, and monitoring for your application. It helps you monitor the application’s state, metrics, and environment through various endpoints.

Question 7: How do you enable Actuator endpoints in Spring Boot? Answer: You enable Actuator endpoints by including the ´spring-boot-starter-actuator´ dependency in your ´pom.xml´ or ´build.gradle´ file. You can then configure which endpoints to expose in your ´application.properties´ file.

Question 8: How do you customize Actuator endpoints in Spring Boot? Answer: You customize Actuator endpoints by setting properties in your ´application.properties´ file, such as ´management.endpoints.web.exposure.include=* to expose all endpoints or specify individual endpoints to include or exclude.

Question 9: How do you integrate Spring Boot with Prometheus for monitoring? Answer: You integrate Spring Boot with Prometheus by adding the micrometer-registry-prometheus dependency. You then configure Prometheus to scrape metrics from the ´ /actuator/prometheus´ endpoint provided by Actuator.

Question 10: How do you set up health checks in Spring Boot? Answer: You set up health checks in Spring Boot using Actuator’s health endpoint. By default, it includes several health indicators. You can add custom health indicators by implementing the ´HealthIndicator´ interface and registering it as a bean.

Spring Boot helps simplify the development process of Spring applications by providing auto-configuration, embedded servers, and production-ready features out of the box. 

By understanding the concepts and features of the topic, one can effectively communicate their knowledge during Spring Boot interview questions. 

This further helps in demonstrating the interviewee’s learning skills and proficiency with the popular framework while also increasing their chances of success. 

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FAQs

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