Spring Boot Interview Questions

5/29/202312 min read

Q1. What is Spring Boot?

Spring Boot is a framework that simplifies the development of Java applications by providing pre-configured settings and configurations. It allows developers to quickly set up and run standalone, production-grade Spring-based applications, without the need for manual configuration.

With Spring Boot, developers can focus on writing business logic rather than boilerplate code, as it eliminates the need for XML configuration files and reduces the overall setup time.

Spring Boot also provides a range of features, including embedded servers, dependency management, and automatic configuration, which make it easier to build and deploy applications. It is widely used in the industry due to its simplicity and productivity enhancements, making it a popular choice for developing microservices and web applications.

Q2. What are the advantages of Spring Boot?

Spring Boot offers several advantages for developers.

First, it simplifies the process of building and deploying applications by providing defaults and auto-configuration. This means developers can focus on writing business logic instead of dealing with boilerplate code.

Second, Spring Boot offers a wide range of starter dependencies, which makes it easy to add common functionality to applications. These starters handle the configuration and wiring of various technologies, such as databases, web servers, and security.

Third, Spring Boot provides a powerful and intuitive command-line interface for running and managing applications. This allows developers to quickly start and stop applications, view logs, and perform other administrative tasks.

Overall, Spring Boot greatly enhances productivity and makes it easier to develop robust and scalable applications.

Q3. What are the different Spring Boot components?

Spring Boot is a powerful framework that is widely used for building Java applications. It consists of several components that work together to simplify the development process.

Spring Boot Starter, which provides a set of preconfigured dependencies that can be easily included in the project.
Spring Boot Actuator, which allows for monitoring and managing the application at runtime. Additionally, Spring Boot includes the Spring Boot CLI, a command-line interface that enables developers to quickly prototype and test their applications.
Spring Boot Autoconfiguration, which automatically configures the application based on the dependencies present.
Spring Boot DevTools, which provides a set of tools for fast application restarts and live reloading.
Overall, these components make Spring Boot a popular choice for building modern and efficient Java applications.

Q4. What are Spring Boot Starters?

Spring Boot Starters are a collection of dependency descriptors that facilitate easy configuration and setup of Spring applications. They provide a convenient way to add required dependencies to your project without having to manually include each one. These starters are essentially a set of pre-defined templates that include all the necessary dependencies for specific functionalities or technologies.

By using Spring Boot Starters, developers can quickly bootstrap their applications and focus on writing business logic instead of worrying about configuring various dependencies. These starters cover a wide range of technologies, such as web, database, security, testing, and more. With Spring Boot Starters, developers can accelerate development, improve productivity, and ensure consistent and reliable application setup.

Q5. Name some of the starters provided by Spring Boot.

1. spring-boot-starter-web – Web and RESTful applications

2. spring-boot-starter-security – Spring Security

3. spring-boot-starter-data-jpa – Spring Data JPA

4. spring-boot-starter-test – Unit testing

5. spring-boot-starter-hateoas – Add HATEOAS features

6. spring-boot-starter-data-jpa – Spring Data JPA with Hibernate

Q6. What is Auto-Configuration in Spring Boot?

Auto-Configuration in Spring Boot is a powerful feature that allows developers to automatically configure Spring applications based on the dependencies present in the classpath. This feature eliminates the need for manual configuration, saving developers time and effort.

When an application starts, Spring Boot scans the classpath for specific dependencies and automatically configures the beans and configuration classes accordingly. This makes it easier for developers to create Spring applications without having to worry about the intricate details of configuration.

Auto-Configuration also provides a way to customize the default behavior by using properties files or annotations. Overall, Auto-Configuration in Spring Boot simplifies the development process and enhances productivity by automatically configuring the application based on the dependencies present.

Q7. What are the different options for creating the Spring Boot application?

There are several options available for creating a Spring Boot application.

Spring Initializr, which is a web-based tool that allows you to generate a Spring Boot project with the desired dependencies and configuration.

Integrated development environment (IDE) such as IntelliJ or Eclipse, which provide built-in support for creating Spring Boot applications.

Additionally, you can also create a Spring Boot application using the command line by using the Spring Boot CLI tool. This tool allows you to quickly create and run Spring Boot applications without the need for an IDE. Overall, there are various options available for creating a Spring Boot application, allowing developers to choose the approach that best suits their needs and preferences.

Q8. Can we use Spring Boot for non-Spring applications?

Yes, Spring Boot can be used for non-Spring applications. Spring Boot is a framework that is built on top of the Spring framework, but it also provides a standalone option for developers who do not want to use Spring. It allows developers to easily create standalone applications with minimal configuration. With Spring Boot, you can build applications using Java, Kotlin, or Groovy. It provides a range of features and capabilities, including auto-configuration, which automatically configures the application based on its dependencies, and embedded server support. So even if you are not using Spring, you can still take advantage of the benefits that Spring Boot offers, such as faster development, simplified deployment, and improved productivity.

Q9. What is the Spring Boot Initilizr?

The Spring Boot Initializr is a web-based tool that allows developers to quickly generate and customize Spring Boot projects. It simplifies the process of setting up a new Spring Boot application by providing a user-friendly interface to select the desired dependencies, features, and configurations. The Initializr supports various options for project type, language, packaging, and build system, allowing developers to tailor their projects to their specific needs. Once the desired options are selected, the Initializr generates a project template with the necessary files and configurations, which can be downloaded and imported into an Integrated Development Environment (IDE). This tool greatly speeds up the initial setup process and helps developers get started with building Spring Boot applications efficiently.

Q10. What are the advantages of Spring Boot Initializr?

Spring Boot Initializr is a powerful tool that offers several advantages.

It provides a quick and easy way to create Spring Boot projects by generating the necessary project structure and dependencies.
This saves developers valuable time as they don't have to manually set up the project from scratch.
Initializr allows developers to customize their project by selecting specific dependencies and configurations. This ensures that the project is tailored to their specific needs, leading to more efficient development.
Moreover, Initializr provides a user-friendly interface that makes it easy to navigate and understand the project configuration options. This enables even beginners to quickly get started with Spring Boot and build robust applications.

Overall, the advantages of Spring Boot Initializr make it an indispensable tool for developers looking to streamline their Spring Boot project setup process.

Q11. How can I reload my Spring Boot changes without restarting the server?

To reload your Spring Boot changes without restarting the server, you can use the hot swapping feature provided by Spring Boot DevTools. This feature allows you to automatically reload modified classes without the need for a server restart.

To enable this feature, you need to include the DevTools dependency in your project's pom.xml or build.gradle file.

pom.xml

<groupId>org.springframework.boot</groupId>

<artifactId>spring-boot-devtools</artifactId>

</dependency>

</dependencies>

build.gradle

implementation group: 'org.springframework.boot', name: 'spring-boot-devtools'

Once enabled, any changes you make in your Spring Boot application's code will be automatically detected and applied by the DevTools. This can greatly improve your development workflow as you no longer have to manually restart the server every time you make a change. Just save your changes and they will be instantly reflected in your running application.

Q12. What are embedded containers supported by Spring Boot?

Spring Boot supports the main three embedded containers:

Tomcat
Jetty
Undertow

By default, it uses Tomcat as an embedded container.

Q13. What is the Spring Boot Actuator?

The Spring Boot Actuator is a module that provides a set of production-ready features to monitor and manage the Spring Boot application. With Actuator, developers can easily access various endpoints to gather metrics, health checks, and perform other operational tasks.

The actuator provides features like auditing, health, metrics, environment information, thread dump etc. using HTTP endpoints. Actuator also allows developers to customize and expose additional endpoints based on specific requirements. This module plays a crucial role in enhancing the observability and maintainability of Spring Boot applications.

Q14. How to run Spring Boot application to custom port?

To run a Spring Boot application on a custom port, you need to make a small modification in the application.properties file. Open the file and add the following line: `server.port=your_custom_port_number`. Replace `your_custom_port_number` with the port number you want to use. Save the file and then run the application. It will now start on the specified port. To verify if it is running on the custom port, you can check the console output or use a web browser to access the application using `http://localhost:your_custom_port_number`. This will ensure that your Spring Boot application is running on the desired port.

eg. server.port=9001

Q15. What is a shutdown in the actuator?

A shutdown is an endpoint that helps an application to be shut down properly. This feature is not enabled by default. However, you can use it by setting the command: management.endpoint.shutdown.enabled=true in your application.properties file.

Q16.Is it possible to replace or override the Embedded Tomcat server in Spring Boot?

Yes, it is possible to replace or override the Embedded Tomcat server in Spring Boot. Spring Boot provides the flexibility to choose a different embedded server by simply excluding the default Tomcat dependencies and adding the desired embedded server dependencies.

For example, if you want to use Jetty as the embedded server, you can exclude the Tomcat dependencies by adding the following exclusion in your pom.xml file:

Find the following dependency in pom.xml:

Replace it with:

Then, you can add the Jetty dependency in your pom.xml file:

By making these changes, you can easily replace the default Tomcat server with Jetty or any other supported embedded server in Spring Boot.

Q17.Can you disable the default web server in the Spring Boot application?

Yes, it is possible to disable the default web server in a Spring Boot application. By default, Spring Boot uses an embedded web server, such as Tomcat or Jetty, to serve the application. However, if you want to disable this default web server, you can do so by excluding the embedded servlet container dependency from your project's dependencies. This can be achieved by modifying the pom.xml file or the build.gradle file, depending on whether you are using Maven or Gradle. Once you have excluded the embedded servlet container dependency, you can deploy your Spring Boot application to an external web server or container of your choice. This gives you the flexibility to use a different web server or container that better suits your requirements.

Q18. What logging support provided by Spring Boot? How can we control the logging level in Spring Boot?

Spring Boot provides comprehensive logging support through its integration with several popular logging frameworks such as Logback, Log4j2, and JUL (java.util.logging). By default, Spring Boot uses Logback as the default logging framework. However, you can easily switch to another logging framework by including the relevant dependencies in your project. Spring Boot also provides a default logging configuration that can be customized according to your needs. You can configure logging levels, log format, and appenders to direct logs to various destinations such as the console, files, or remote servers. Additionally, Spring Boot automatically configures logging for different profiles, allowing you to have different logging configurations for different environments.

In Spring Boot, we have the ability to control the logging level through various configurations. One way to do this is by modifying the "application.properties" or "application.yml" file in our project. By setting the "logging.level" property, followed by the package or class name, to a specific logging level such as "DEBUG", "INFO", or "ERROR", we can adjust the verbosity of the logs produced by that specific package or class. Another option is to use annotations provided by Spring Boot, such as "@Slf4j" or "@Log4j2", which automatically configure the logging level based on the given annotation. Additionally, we can customize the logging configuration using a "logback.xml" or "log4j2.xml" file, where we can specify the desired logging levels for different packages or classes. Overall, Spring Boot offers multiple approaches to control the logging level, allowing developers to effectively manage the amount of information logged during runtime.

Q19. How to implement security for Spring Boot application?

To implement security for a Spring Boot application, you can utilize the Spring Security framework. Spring Security provides a wide range of features and configurations to secure your application. Firstly, you need to add the Spring Security dependency to your project's build file. Once added, you can configure the security settings in the application's configuration class by extending the WebSecurityConfigurerAdapter. This allows you to customize authentication and authorization rules, define login and logout endpoints, and configure access to different resources. Additionally, you can integrate with various authentication providers such as LDAP, OAuth, or a custom authentication provider. It is also recommended to handle session management and enable HTTPS for secure communication. By following these steps, you can effectively secure your Spring Boot application against unauthorized access and protect sensitive information.

Use the spring-boot-starter-security starter to enable the Spring security support in your Spring Boot application.

Q20. How to configure database using Spring Boot?

To configure a database using Spring Boot, you need to define the necessary properties in the application.properties file. Firstly, you need to specify the driver class name and the database URL. This information will depend on the type of database you are using. Next, you need to provide the username and password for accessing the database.

The above example is to configure MySQL in your application.

Q21. Explain @SpringBootApplication annotation of Spring Boot?

The @SpringBootApplication annotation is a convenience annotation that is used to bootstrap a Spring Boot application. It is often used as the main entry point for the application. The annotation combines three important annotations: @Configuration, @EnableAutoConfiguration, and @ComponentScan.

@Configuration indicates that the class should be considered as a configuration class, defining beans and their dependencies.

@EnableAutoConfiguration enables Spring Boot's auto-configuration mechanism, which automatically configures the application based on the classpath and other configuration properties.

@ComponentScan tells Spring to scan the specified package and its sub-packages for components, such as controllers and services, that need to be managed by Spring.

By combining these three annotations, the @SpringBootApplication annotation simplifies the configuration and initialization of a Spring Boot application. It provides a concise and convenient way to set up a basic Spring Boot project.

Q22. Explain Spring Boot annotations.

Spring Boot annotations are a set of directives that simplify the development process of Spring applications. These annotations are used to configure various aspects of the application, such as defining the main class, managing dependencies, and handling the lifecycle of components. The @SpringBootApplication annotation, for example, combines multiple annotations to enable auto-configuration, component scanning, and the creation of Spring beans. Other commonly used annotations are :

@GetMapping annotation is used to handle HTTP GET requests. It is a shortcut for @RequestMapping(method = RequestMethod.GET) which maps the specified URL pattern to a method in the controller class. When a GET request is made to the specified URL, the corresponding method is invoked and its return value is sent back as the response. This annotation is commonly used to retrieve data from a server or to access a specific resource. It provides a convenient way to handle GET requests and allows for cleaner and more organized code.

@PostMapping annotation is used in Java Spring to handle HTTP POST requests. It is a shortcut for @RequestMapping(method = RequestMethod.POST). By using this annotation, we can map a specific URL path to a method that will handle the POST request. The method annotated with @PostMapping will be executed when a POST request is made to the specified URL path. This annotation is commonly used when creating RESTful APIs or when implementing form submissions in web applications. The @PostMapping annotation provides a convenient way to handle POST requests and helps in organizing and structuring the code.

The description provided consists of various annotations and annotations-related terms used in the Java programming language, specifically in the context of building RESTful web services using Spring MVC framework. These annotations are used to handle HTTP requests and responses, as well as to bind request parameters and headers to method arguments.

The @PutMapping, @DeleteMapping, and @PatchMapping annotations are used to handle HTTP methods - PUT, DELETE, and PATCH respectively.

@RequestBody annotation is used to bind the request body to a method parameter, while the @ResponseBody annotation is used to indicate that the return value should be serialized and included in the response body.

@PathVariable annotation is used to bind a method parameter to a path variable in the request URL.

@RequestParam annotation is used to bind a method parameter to a request parameter, and the @RequestHeader annotation is used to bind a method parameter to a request header.

@RestController annotation is used to indicate that a class is a REST controller, and the @RequestAttribute and @ModelAttribute annotations are used to bind request attributes and model attributes to method parameters respectively.

Q23. What is the difference between @Controller and @RestController?

The difference between @Controller and @RestController lies in the way they handle HTTP responses. The @Controller annotation is used to create a controller class that handles requests and returns a view by using a view resolver. On the other hand, the @RestController annotation is used to create a RESTful web service controller that returns the response directly in a format like JSON or XML, without the need for a view resolver.

The @RestController annotation combines the @Controller and @ResponseBody annotations, making it easier to build RESTful APIs. So, if you are building a web application that requires views, you would typically use the @Controller annotation. However, if you are building a RESTful API that only needs to return data, the @RestController annotation is more suitable.

Q23. What is the difference between @Controller and @RestController?

Q24. What is Dependency Injection?

Dependency Injection is a software design pattern that allows for loose coupling between software components. It is a way to implement the principle of inversion of control, where the control flow is inverted from the traditional approach.

In Dependency Injection, the dependencies of a class are injected or provided externally, rather than the class itself creating or managing them. This promotes modularity, testability, and maintainability of the codebase. By decoupling the components, changes can be made to one component without affecting others, making the code more flexible and easier to maintain. Dependency Injection can be implemented using different techniques, such as constructor injection, setter injection, or interface injection. Overall, Dependency Injection is a powerful tool that helps improve the overall architecture and quality of software systems.

Types of Dependency Injection:

Constructor-based Dependency Injection
Setter-based Dependency Injection
Field or Property-based Dependency Injection

Spring Boot Interview Questions

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