Essential Spring Boot Interview Questions

If you are preparing for a Spring Boot interview or simply looking to enhance your knowledge of this powerful Java framework, you’ve come to the right place. In this page, we will delve into a collection of commonly asked interview questions related to Spring Boot. From fundamental concepts to advanced topics, we will cover essential areas such as dependency injection, auto-configuration, handling properties, and more.

By the end of this page, you will have a solid understanding of key Spring Boot concepts and be well-prepared to tackle interview questions with confidence. So, let’s dive in and explore the world of Spring Boot together!

By the way, you might also be interested in checking Spring Framework Interview Questions.

Table of Contents

What is Spring Boot?

Spring Boot is a powerful Java-based framework that simplifies the development of stand-alone, production-grade applications. It provides a comprehensive platform for building enterprise-level applications with minimal configuration and boilerplate code.

With Spring Boot, developers can quickly create robust, scalable, and easily deployable applications by leveraging the features and capabilities of the underlying Spring ecosystem. It promotes convention-over-configuration, enabling developers to focus more on business logic rather than intricate setup and infrastructure concerns.

In essence, Spring Boot empowers developers to rapidly build and deploy Spring-based applications with increased efficiency and reduced time-to-market.

Learn more at: Spring Boot: Getting Started Guide.

Why should one consider using Spring Boot and what benefits does it offer?

Spring Boot offers several advantages that make it a popular choice for developing Java applications. Firstly, it provides a simplified and opinionated approach to application setup and configuration. With its convention-over-configuration principle, developers can quickly get started without the need for extensive boilerplate code.

Secondly, Spring Boot includes embedded application servers, such as Tomcat, Jetty, or Undertow, eliminating the need for manual server setup. This feature enhances development productivity and simplifies deployment.

Another benefit is Spring Boot’s auto-configuration feature, which automatically configures various components based on the project’s dependencies. This reduces manual configuration efforts and enables developers to focus on application logic rather than infrastructure setup.

Furthermore, Spring Boot offers seamless integration with other Spring projects and a vast ecosystem of plugins, making it highly extensible and adaptable to different development needs.

Overall, the advantages of using Spring Boot lie in its simplicity, productivity, auto-configuration capabilities, and strong integration with the Spring ecosystem, which collectively contribute to faster development cycles and easier maintenance of Java applications.

What are the Spring Boot key components?

Spring Boot is composed of several key components that simplify the development of Java applications. The main components of Spring Boot include:

Spring Framework: Spring Boot builds upon the Spring Framework, providing powerful features and tools for developing enterprise-grade applications.
Auto-configuration: Spring Boot’s auto-configuration feature automatically configures beans and dependencies based on the application’s classpath and libraries used. This eliminates the need for manual configuration and reduces boilerplate code.

Embedded Server: Spring Boot includes an embedded server, such as Tomcat, Jetty, or Undertow, which allows applications to be deployed as standalone executables without requiring a separate application server.
Starter Dependencies: Spring Boot offers a wide range of starter dependencies that simplify the management of project dependencies. These starters provide pre-configured dependencies for specific technologies, such as databases, web services, or security.
Actuator: Actuator provides production-ready features for monitoring and managing Spring Boot applications. It offers endpoints to retrieve information about the application’s health, metrics, and more.

By leveraging these key components, Spring Boot enables developers to rapidly build robust and scalable Java applications with minimal configuration overhead.

What advantages does Spring Boot offer compared to Spring?

Spring Boot provides several advantages over traditional Spring, making it a preferred choice for many developers.

Firstly, Spring Boot simplifies the configuration process by offering convention over configuration. It reduces the need for XML configuration and boilerplate code, allowing developers to focus more on building the application logic.

Additionally, Spring Boot provides embedded servers, making it easier to deploy applications as standalone executables without the need for external server setups.

Furthermore, Spring Boot includes auto-configuration, which automatically configures various components based on the classpath dependencies. This feature saves developers from manually configuring numerous components, resulting in faster development and reduced boilerplate code.

Overall, Spring Boot enhances productivity, promotes rapid application development, and reduces the complexity associated with traditional Spring applications.

Which starter dependency is typically used in the Spring Boot module?

In the Spring Boot module, the most commonly used starter dependency is the “spring-boot-starter-parent.” This starter provides essential configurations and dependencies required for Spring Boot applications.

It serves as the parent project for other Spring Boot starters, enabling developers to easily bootstrap their projects and leverage the features and capabilities provided by the Spring Boot framework.

Here are some of the most common starter dependencies used in Spring Boot applications:

spring-boot-starter-web: Provides the necessary dependencies to build web applications with Spring MVC.
spring-boot-starter-data-jpa: Enables the use of Spring Data JPA for database access and ORM (Object-Relational Mapping) functionality.
spring-boot-starter-security: Includes dependencies for implementing security features in Spring Boot applications, such as authentication and authorization.

spring-boot-starter-test: Offers dependencies for testing Spring Boot applications, including frameworks like JUnit and Mockito.
spring-boot-starter-thymeleaf: Provides the necessary dependencies for using the Thymeleaf template engine in Spring Boot for server-side rendering.
spring-boot-starter-actuator: Enables monitoring and managing Spring Boot applications by exposing various management endpoints.

These starter dependencies are widely used in Spring Boot projects and serve as a foundation for incorporating specific functionalities into the applications.

What is the functioning mechanism of Spring Boot?

Spring Boot operates by simplifying the development process of Spring-based applications. It achieves this by providing pre-configured defaults and auto-configuration capabilities.

By leveraging annotations, Spring Boot effortlessly configures your application based on the project’s added dependencies. The central point of entry for a Spring Boot application is the class adorned with the @SpringBootApplication annotation, housing the main method.

Additionally, Spring Boot seamlessly conducts component scanning within the project, facilitated by the @ComponentScan annotation. This process ensures that all relevant components are automatically detected and incorporated into the application’s runtime environment.

Learn more at: Component Scanning in a Spring Boot Application.

How does the @SpringBootApplication annotation work?

The @SpringBootApplication annotation serves as a combination of three annotations: @Configuration, @EnableAutoConfiguration, and @ComponentScan.

Internally, the @Configuration annotation indicates that the class contains Spring bean definitions. @EnableAutoConfiguration enables Spring Boot’s auto-configuration feature, which automatically configures the application based on classpath settings and dependencies. Lastly, @ComponentScan scans the specified package and its sub-packages for Spring components, such as controllers and services, to be registered in the application context.

In summary, the @SpringBootApplication annotation internally enables configuration, automatic configuration, and component scanning, making it a powerful and convenient way to bootstrap a Spring Boot application.

Learn more at: Component Scanning in a Spring Boot Application. / @Configuration Annotation in Spring Boot.

Why is the @ComponentScan annotation used in class files and what purpose does it serve?

The @ComponentScan annotation in Spring Boot allows for the automatic detection and registration of Spring beans within a specified package or packages. It enables the Spring container to locate and instantiate these beans, making them available for dependency injection and other Spring features. Essentially, @ComponentScan helps with component scanning, which is crucial for the framework to identify and manage beans effectively.

Learn more at: Component Scanning in a Spring Boot Application.

What is the process of starting a Spring Boot application?

To begin a Spring Boot application, the main entry point is the main() method, which resides in a class annotated with @SpringBootApplication. This annotation combines multiple annotations that configure and bootstrap the application.

When the main() method is executed, Spring Boot uses an embedded servlet container to start the application, initializes the necessary beans, and scans the classpath for components and configurations.

In summary, a Spring Boot application starts by invoking the main() method in the annotated class, triggering the auto-configuration and initialization process.

In Spring Boot, what do we mean by “starter dependencies,” and why are they important?

Starter dependencies in Spring Boot are curated sets of preconfigured libraries that help streamline application development. They are designed to provide all the necessary dependencies and configuration needed for specific functionalities or technologies.

By including a starter dependency, developers can easily add features to their Spring Boot projects without having to manually manage individual dependencies. These starters simplify the development process by reducing the configuration overhead and ensuring that the required dependencies are readily available.

Learn more at: A List of Spring Boot Starters.

What role does Spring Initializer play in starting Spring Boot projects?

Spring Initializer is a web-based tool that helps developers kickstart Spring Boot projects by generating a basic project structure with the required dependencies and configurations based on the selected options.

Learn more at: Create Spring Boot Project with Spring Initializr.

What are the advantages of using Spring Boot CLI?

Spring Boot CLI is a command-line interface tool that allows developers to quickly build and test Spring Boot applications. It provides a streamlined way to develop applications by automating the configuration and setup process.

Some benefits of using Spring Boot CLI include:

Rapid application development: With its concise commands, Spring Boot CLI enables developers to create Spring Boot projects and prototypes swiftly.
Simplified configuration: The CLI automatically configures dependencies and settings, reducing the manual effort required for setup.
Easy deployment: Spring Boot CLI simplifies the deployment process by packaging applications as standalone JAR files, making them easy to run on any Java environment.

Enhanced productivity: By eliminating boilerplate code and providing a productive environment, Spring Boot CLI helps developers focus on writing business logic rather than infrastructure-related tasks.

Learn more at: Installing Spring Boot CLI.

What are some frequently used Spring Boot CLI commands?

The Spring Boot CLI (Command Line Interface) offers several commonly used commands for efficient development and deployment. Here are a few essential ones:

spring run: Executes a Spring Boot application.
spring init: Creates a new Spring Boot project.
spring test: Runs tests for a Spring Boot application.

spring jar: Builds an executable JAR file for a Spring Boot application.
spring stop: Stops a running Spring Boot application.

These commands streamline the development process and enhance productivity when working with Spring Boot projects.

Which essential annotations does Spring Boot provide?

Spring Boot provides several essential annotations that simplify the development process and enhance the functionality of your applications. These annotations play a crucial role in configuring various aspects of your Spring Boot projects. Some of the fundamental annotations offered by Spring Boot include:

@SpringBootApplication: This annotation combines three commonly used annotations, namely @Configuration, @EnableAutoConfiguration, and @ComponentScan. It marks the entry point of a Spring Boot application and enables auto-configuration and component scanning.
@RestController: This annotation is used to define a RESTful controller, which handles incoming HTTP requests and returns the appropriate responses. It combines the functionalities of @Controller and @ResponseBody annotations.

@RequestMapping: This annotation is used to map a URL path or HTTP request method to a specific method in a controller. It helps in routing the incoming requests to the appropriate controller methods.
@Autowired: This annotation is used for automatic dependency injection. It allows Spring Boot to automatically wire the dependencies required by a class, simplifying the wiring process.
@Configuration: This annotation indicates that a class defines Spring Bean configurations. It is commonly used in conjunction with @Bean annotations to create and configure beans.

These are just a few examples of the basic annotations offered by Spring Boot. Utilizing these annotations effectively can greatly streamline your Spring Boot development process and improve the overall efficiency of your applications.

Learn more at: Spring Core Annotations with Examples.

How does Spring Boot dependency management simplify the handling of dependencies in a Spring Boot application?

Spring Boot dependency management is a powerful feature that simplifies the management of dependencies in a Spring Boot application. It provides a curated set of starter dependencies, which are pre-configured libraries that enable specific functionalities. This eliminates the need for manual dependency version management and ensures compatibility among the dependencies used in the application.

Is it possible to develop a non-web application using Spring Boot?

Yes, Spring Boot is not limited to web applications only. It can be used to create various types of applications, including non-web applications. Spring Boot provides a lightweight and convenient framework for developing standalone applications, batch processing systems, command-line tools, and more. Its modular design and extensive library support make it suitable for a wide range of application development scenarios, both web and non-web.

Can the port of the embedded Tomcat server be modified in Spring Boot?

Yes, it is indeed possible to change the port of the embedded Tomcat server in Spring Boot. Spring Boot provides a simple and flexible way to configure the server properties, including the port number.

By default, the embedded Tomcat server runs on port 8080, but you can easily change it to any desired port number by specifying the appropriate property in the application.properties or application.yml file.

For example, you can set the server port to 9090 by adding server.port=9090 in the configuration file. This allows you to customize the port based on your application’s requirements or to avoid conflicts with other services running on the same server.

Learn more at: Start Spring Boot Application on a Different Port Number.

Is it possible to override or replace the default Embedded Tomcat server used in Spring Boot?

Spring Boot provides flexibility in choosing the embedded server for your application. While it comes bundled with an embedded Tomcat server by default, you can easily override or replace it with other servers such as Jetty or Undertow.

To change the embedded server, you need to exclude the Tomcat dependency and include the desired server dependency in your project’s build configuration. Additionally, you may need to make some adjustments in the application properties or configuration files to ensure compatibility with the new server.

Is it possible to deactivate the default web server in a Spring Boot application?

Yes, it is possible to disable the default web server in a Spring Boot application. Spring Boot provides a convenient way to configure and customize various aspects of the application, including the web server.

By excluding the embedded web server dependency from the project’s dependencies or by configuring the appropriate properties in the application configuration, you can disable the default web server.

This can be useful in scenarios where you want to use Spring Boot primarily for background processing or for building non-web applications. Disabling the default web server allows you to optimize the application’s resources and improve its overall performance.

If you wish to deactivate a particular auto-configuration class in Spring Boot, what steps should you take?

If you have a specific class for which you don’t want the auto-configuration to be applied, you can utilize the exclude attribute of the @EnableAutoConfiguration annotation. By specifying the class name within the exclude attribute, you can ensure that the auto-configuration is not applied to that particular class.

What is the purpose of the @RestController annotation in Spring Boot, and how does it differ from the @Controller annotation?

The @RestController annotation in Spring Boot is used to create RESTful web services. It combines the functionality of the @Controller annotation and the @ResponseBody annotation. When a class is annotated with @RestController, it automatically includes the @ResponseBody annotation for all its methods.

This means that the return values from the methods are directly serialized into the HTTP response body as JSON or XML, without the need for additional annotations.

In summary, the @RestController annotation simplifies the creation of RESTful web services in Spring Boot by eliminating the need for separate annotations and providing automatic serialization of response objects.

How does the Spring Boot application handle the flow of HTTPS requests?

When a client initiates an HTTPS request in a Spring Boot application, the flow goes through a series of steps. First, the request is received by the embedded server, such as Apache Tomcat or Undertow, which acts as the entry point for the application. The server then performs the SSL/TLS handshake to establish a secure connection with the client.

Once the connection is established, the request is passed to the Spring DispatcherServlet, which acts as the front controller. The DispatcherServlet determines the appropriate Spring MVC controller to handle the request based on the configured request mappings. The controller then processes the request and generates a response.

Throughout this process, the Spring Security module can be employed to handle security-related tasks, such as authentication and authorization. It can intercept the request and apply security filters to ensure that the client has the necessary permissions to access the requested resources.

After the request has been processed by the controller and any necessary security checks have been performed, the response is returned to the client through the established HTTPS connection. The client receives the response and can further process it as needed.

Overall, the flow of HTTPS requests in a Spring Boot application involves the embedded server, the DispatcherServlet, Spring MVC controllers, and potentially the Spring Security module to handle security-related aspects.

Can you explain the distinction between RequestMapping and GetMapping in Spring Boot?

RequestMapping and GetMapping are annotations used in Spring Boot to handle incoming HTTP requests. While both annotations are used to map a method to a specific URL, they have a slight difference in their usage.

GetMapping is a specialized form of RequestMapping that is specifically used for handling GET requests. It is used to map a method to a particular URL endpoint, indicating that the method should be executed when a GET request is made to that endpoint. GetMapping simplifies the code and makes it more readable by explicitly specifying that the method is meant to handle GET requests.

On the other hand, RequestMapping is a more general annotation that can be used to handle different types of HTTP requests such as GET, POST, PUT, DELETE, etc. It provides flexibility by allowing you to handle multiple request methods using a single method. By default, if no specific method is mentioned in the RequestMapping annotation, it will handle all types of requests.

In summary, while GetMapping is specifically used for handling GET requests, RequestMapping can handle various types of HTTP requests and provides more flexibility in mapping methods to URL endpoints.

Learn more at: The @RequestMapping Annotation: A Comprehensive Guide.

Why are Profiles important in Spring Boot and how do they enhance application development?

Profiles in Spring Boot are a powerful feature that allows developers to define different configurations for their applications based on specific environments or use cases. By utilizing profiles, developers can easily customize application behavior, properties, and dependencies, ensuring seamless deployment across various environments such as development, testing, and production.

With profiles, developers can isolate and manage environment-specific configurations without modifying the underlying codebase. This flexibility enables efficient development and simplifies the deployment process. For instance, you can have separate database configurations for different environments, define specific logging levels, or enable/disable certain features based on the profile in use.

Overall, profiles in Spring Boot streamline application configuration, enhance maintainability, and contribute to the overall robustness of the system by ensuring that the right settings are applied in the appropriate environments.

Learn more at: Spring Boot Profiles Tutorial.

What is the purpose of Spring Actuator, and what benefits does it offer?

Spring Actuator is a powerful feature in Spring Boot that provides production-ready monitoring and management capabilities for your application. It enables you to gather crucial insights and operational information about your Spring Boot application at runtime. By exposing various endpoints and metrics, Spring Actuator empowers you to monitor and manage your application’s health, performance, and other essential aspects.

Advantages of Spring Actuator include:

Monitoring and health checks: Spring Actuator offers a wide range of endpoints, such as /health and /metrics, allowing you to monitor the health and performance of your application in real-time.
Custom endpoint exposure: You can also create custom endpoints with valuable information specific to your application and expose them via Spring Actuator.
Integration with external systems: Spring Actuator seamlessly integrates with popular monitoring systems like Prometheus, Graphite, and others, enabling you to collect and analyze metrics in your preferred monitoring tools.

Security and access control: Spring Actuator provides configurable security measures, allowing you to secure the sensitive endpoints and restrict access based on roles and permissions.
Troubleshooting and diagnostics: With Spring Actuator, you can retrieve detailed information about various application components, request mappings, and beans, facilitating easier troubleshooting and diagnostics.

In summary, Spring Actuator enhances your Spring Boot application by offering extensive monitoring, management, and troubleshooting capabilities, empowering you to build robust and well-performing applications.

Learn more at: Spring Boot Actuator Tutorial.

What steps are involved in enabling Actuator in a Spring Boot application?

Open the application.properties or application.yml file of your project.
Add the following property: management.endpoints.web.exposure.include=* (for application.properties) or management: endpoints: web: exposure: include: '*' (for application.yml).

This configuration will enable all Actuator endpoints, allowing you to monitor and manage your application.

Enabling Actuator in a Spring Boot application involves modifying the configuration file to include the appropriate property that grants access to Actuator endpoints.

What is the purpose of the actuator-provided endpoints in monitoring a Spring Boot application?

The actuator-provided endpoints in Spring Boot serve as a powerful tool for monitoring and managing the application. These endpoints offer valuable insights into the application’s health, metrics, environment, and more. With actuator endpoints, developers can gather crucial information about the application’s performance, troubleshoot issues, and make informed decisions for optimizing its behavior.

Here are the actuator-provided endpoints commonly used for monitoring a Spring Boot application:

/health: Provides information about the application’s health status, indicating whether it is up and running or encountering any problems.
/info: Displays general information about the application, such as its name, version, and description.

/metrics: Offers various metrics about the application, including memory usage, request counters, thread usage, and more.
/env: Shows the current environment variables and their values for the application.
/logfile: Allows access to the application’s log file, providing insights into recent events and debugging information.

/trace: Presents a trace of recent HTTP requests handled by the application, including request and response details.
/dump: Provides a thread dump of the application, aiding in diagnosing issues related to thread contention or deadlock.
/actuator: Serves as the main entry point for accessing all available actuator endpoints. It offers a comprehensive overview of all available endpoints and their documentation.

What is the approach to retrieve the complete list of beans in a Spring Boot application?

To obtain the comprehensive list of beans in your Spring Boot application, you can utilize the ApplicationContext class. By accessing the ApplicationContext, you can employ the getBeanDefinitionNames() method, which returns an array of strings containing the names of all the beans registered in the application context.

This method allows you to dynamically retrieve the bean names and analyze the bean configuration programmatically. It is a valuable technique when you need to gain insights into the beans present within your Spring Boot application.

To examine the environment properties within your Spring Boot application, what steps should you take?

When working with a Spring Boot application, you can easily access the environment properties by injecting the Environment object. Here’s a brief overview of the process:

Inject the Environment object into your class by using the @Autowired annotation.
Utilize the getProperty() method provided by the Environment object to retrieve specific properties. You can pass the property name as an argument to this method.
Alternatively, you can use the getRequiredProperty() method if you want to ensure that the property exists, throwing an exception otherwise.

Additionally, you can access all properties through the getPropertySources() method, which returns a collection of PropertySource objects. These sources contain the key-value pairs of the properties.

What steps can be taken to activate debugging logs in a Spring Boot application?

To enable debugging logs in a Spring Boot application, you can follow these steps:

Open the application.properties or application.yml file of your Spring Boot project.

Add the following line to the file: logging.level.<package-name>=DEBUG, where <package-name> is the package for which you want to enable debugging logs.
Save the changes and restart your Spring Boot application.

By configuring the logging level to “DEBUG” for the specified package, you allow the application to log more detailed information, which can be helpful during debugging and troubleshooting processes. Remember to set the logging level back to an appropriate value in a production environment to avoid unnecessary log noise.

In a Spring Boot application, where can we specify the configuration properties?

In a Spring Boot application, properties can be defined in various locations, but the most common approach is to use the application.properties or application.yml file. These files are typically placed in the src/main/resources directory of the project. The properties specified in these files can be accessed throughout the application using the @Value annotation or the @ConfigurationProperties annotation.

Additionally, properties can also be provided through command-line arguments, environment variables, or external property files.

Conclusion

In conclusion, this page has provided a comprehensive overview of some common Spring Boot interview questions. We have explored key topics such as the core features of Spring Boot, dependency injection, auto-configuration, and handling properties in a Spring Boot application.

By familiarizing yourself with these interview questions and their answers, you can confidently navigate Spring Boot interviews and demonstrate your expertise in developing robust and efficient applications using this popular Java framework. Ensure you explore the Spring Boot page to access insightful tutorials.