This guide covers the 20 most common Spring Boot interview questions and their answers. Spring Boot is an excellent choice for both beginners and experienced Java developers. Several IT companies, including Google, Netflix, and Amazon use it to propel their product development.
20 Spring Boot Interview Questions and Answers
Welcome to the world of Spring Boot! Spring Boot is a powerful tool for building Java applications, and these questions will help you learn the basics. However, we are also leaving you with a table of references. It included the most visited interview questions from our blog.
To get the best results from this Spring Boot questionnaire, carefully read these interview questions.
What problem does Spring Boot solve, and why is it so popular?
Spring Boot makes application building simple in a variety of ways. It offers several valuable features: auto-setup, dependency sets, and built-in tools, all contributing to the simplification of the development and deployment of Spring applications.
Spring Boot is popular in the Java ecosystem because it makes working on the Spring project a breeze. Moreover, it has a large community of active users and a market with many third-party libraries and integrations available.
Also Read – Difference Between Spring and Spring Boot
What benefits does Spring Boot offer for microservices development?
When it comes to developing microservices, Spring Boot provides several key advantages that simplify the process and enhance efficiency. Below is a summary table highlighting the primary benefits:
| Benefit | Description |
|---|---|
| Simplified Configuration | Focuses on reducing manual configuration, making it well-suited for microservices where simplicity is crucial. |
| Rapid Development | Offers starters that expedite project setup, allowing developers to get started quickly and focus on business logic. |
| Embedded Servers | Provides embedded web servers, simplifying deployment and reducing the operational overhead. |
| Production-level quality | Includes built-in features like health checks and monitoring tools, ensuring applications are ready for production. |
| Scalability | Easily scalable for microservices architecture, allowing for the creation of multiple independent services. |
| Strong Ecosystem Support | Benefits from a robust community and extensive resources for problem-solving and best practices. |
These benefits make Spring Boot an excellent choice for microservices development, streamlining the development and deployment process.
Also Try: Java Spring MVC Quiz
How does Spring Boot differ from the traditional Spring Framework?
Spring Boot not only simplifies the creation of applications but also presents several valuable features. It has auto-setup, dependency sets, and built-in tools, all simplifying the development and deployment of Spring applications.
Traditional Spring Framework is a framework for developing enterprise Java applications. Several key features are available in this old system for building web applications, data access applications, and distributed applications.
| Feature | Spring Boot | Spring Framework |
|---|---|---|
| Auto-configuration | Yes | No |
| Starters | Yes | No |
| Actuators | Yes | No |
| Ease of use | Easier to get started and use | More complex to learn and use |
| Deployment | Easier to deploy to production | More complex to deploy to production |
Overall, Spring Boot makes it a good choice for developers who want to get started with Spring quickly. They can easily develop and deploy Spring applications to production quickly.
Let’s start by setting up and configuring a SpringBoot project. This is the foundation for building any SpringBoot application.
How does Spring Initializr facilitate the creation of a basic Spring Boot app?
To create a basic Spring Boot app using the Initializr, follow these steps:
- Firstly, browse to the Initializr website.
- Select and add the dependencies as per your project.
- Click the “Generate” button.
- Download the generated project and open it in an IDE.
- Run the project as a Java application.
What do you know about Spring Boot auto-config, and how does it work?
Spring Boot auto-config brings simplicity to web app development. It automatically configures many of the common application components such as a web server, database connection, and transaction management.
It works by scanning the classpath for certain types of beans, such as DataSource and EntityManagerFactory. When it finds these beans, it automatically configures them with the appropriate values.
We can customize the auto-configuration by adding properties to a application.properties or YAML file. For example, to change the database connection pool size, you can place the following property in the app’s property file:
Yaml code:
spring.datasource.pool-size=10
Must Try: Java Collection Quiz for Developers
How can you customize Spring Boot’s default behavior?
Spring Boot’s default behavior can be customized by adding properties to the project’s application.properties or YAML file. This file is located in the root of the classpath, and the YAML file is located in the config directory of the classpath.
To customize Spring Boot’s default behavior, simply add a property to the app’s property or the YAML file. The property name should be the same as the name of the property that you want to customize. For example, to customize the database connection pool size, you can place the following property in your project’s application.properties file:
YML code:
spring.datasource.pool-size=10
What is the purpose of the @SpringBootApplication annotation in Spring Boot?
The @SpringBootApplication simplifies the setup of a Spring app by combining the two @Configuration and @ComponentScan. Its main use is to mark a class as the main SpringBoot app.
How do you enable cross-origin resource sharing in the application?
Spring Boot allows enabling CORS with the help of the pom.xml file. Check the below XML.
XML code.
<dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-web</artifactId> </dependency>
Once you have added this dependency, you can enable CORS by adding the following properties to your application.properties file:
spring.cors.enabled=true spring.cors.mapping=/**
This will enable CORS for all endpoints in your SpringBoot application.
You can also configure CORS more granularly by adding @CrossOrigin annotations to individual controllers and methods.
Explain the concept of SpringBoot Starters and provide examples.
SpringBoot starters are Java packages. They are a set of convenient dependency descriptors that you can include in your application. They provide everything we need eliminating the need for manual addition of dependencies. Some examples of the starters include:
a) *-web: This starter adds the dependencies needed to build a web application.
b) *-data-jpa: This starter adds the dependencies needed to connect to a database using JPA.
c) *-security: This starter adds the dependencies needed to secure the application.
To use the Spring Boot starter, simply place it under the dependencies block of your pom.xml file. For example, to add spring-boot-starter-web starter to your project, include the following dep:
XML code:
<dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-web</artifactId> </dependency>
Once you have added the starter to your project, you are all set to start using its features.
What do you know about Spring Boot Actuator, and what is its role?
Spring Boot Actuator is a feature that opens a range of endpoints to monitor and manage the application. These endpoints can be accessed using HTTP requests.
Some of the features that Spring Boot Actuator provides include:
- Health checks: Spring Boot Actuator provides health check endpoints to assess the health status of the application.
- Metrics: Spring Boot Actuator provides metrics endpoints to capture metrics about an application, such as CPU usage, memory usage, and request throughput.
- Trace logging: Spring Boot Actuator provides trace logging endpoints to trace the execution of requests through the application.
Spring Boot Actuator is a valuable tool for monitoring and managing production-ready Spring Boot apps.
How do you handle exceptions in the Spring Boot-based app?
There are two main ways to handle exceptions in this framework:
- Spring Boot Exception Handling: Spring Boot puts forth many options to handle exceptions, such as @ExceptionHandler annotations and global exception handlers.
- Spring MVC Exception Handling: Spring MVC provides several ways to handle exceptions in a Spring MVC app, such as ModelAndView objects and ExceptionHandlerExceptionResolver beans.
Spring Boot Exception Handling is the recommended way to handle exceptions in application code. It is more flexible and easier to use than Spring MVC Exception Handling.
To handle an exception using Spring Boot Exception Handling, you can add an @ExceptionHandler annotation to a method in your controller. The method that you annotate with @ExceptionHandler will be executed when an exception of the specified type occurs.
For example, the following code shows how to handle a SQLException using Spring Boot Exception Handling:
Java Code
@Controller
public class MyController {
@ExceptionHandler(SQLException.class)
public String handleSQLException(SQLException e) {
return "error";
}
}
If a SQLException occurs when a request is processed by the MyController class, the handleSQLException() method will be executed.
What is the role of Spring Boot DevTools in the development process?
Spring Boot DevTools is a tool that makes it easier to develop Spring Boot apps. It has a rich set of features, such as automatic restart and live reload, that can help developers to be more productive.
Spring Boot DevTools is enabled by default in Spring Boot apps. To disable Spring Boot DevTools, you can append the following property to your application.properties file:
spring.devtools.enabled=false
RestAPI allows your application to communicate with other systems. Check related Spring Boot interview questions with answers.
How can you create RESTful APIs in Spring Boot using annotations?
To create a RESTful API endpoint in Spring Boot, you’ll need a controller class and annotate it with the @RestController annotation. The @RestController annotation tells Spring Boot that the class is a REST controller.
Once you have created a REST controller class, you can create methods in the class to handle HTTP requests. To map an HTTP request to a method in a REST controller, try the @RequestMapping annotation. The @RequestMapping annotation specifies the HTTP method and the path of the request.
For example, the following code shows how to create a REST API endpoint that handles GET requests to the /users path:
Java Code
@RestController
public class UserController {
@RequestMapping(value = "/users", method = RequestMethod.GET)
public List<User> getAllUsers() {
// Get all users present in the database
return userRepository.findAll();
}
}
When a GET request is made to the /users path, the Spring Boot framework will execute the getAllUsers() method in the UserController class.
To return a response from a REST API endpoint, you can simply return an object or a collection of objects from the method. Spring Boot will automatically serialize the object or collection of objects to JSON or XML and return it to the client.
Spring Boot makes it easy to work with databases. Check out JPA-related Spring Boot interview questions and answers.
What is JPA (Java Persistence API) in Spring Boot, and how do you use it?
Spring Boot JPA is a tool that makes a programmer’s life easy to work with databases in Spring Boot apps. It is rich in features, such as object-relational mapping (ORM) and transaction management, that can help developers to be more productive.
To use Spring Boot JPA to work with databases, you need to add spring-boot-starter-data-jpa dep to your pom.xml file. Once you have added this dependency, you can create a JPA repository class to interact with the database.
A JPA repository class is an interface that extends the JpaRespository interface. The JpaRespository interface bundles a handful of methods for interacting with the database, such as save(), find(), and delete().
For example, the following code shows a JPA repository class for interacting with the User table:
public interface UserRepository extends JpaRepository<User, Long> {
}
Once you have created a JPA repository class, you can use it to interact with the User table. For example, the following code shows how to save a new User to the database:
UserRepository userRepository = new UserRepositoryImpl();
User user = new User();
user.setName("John Doe");
userRepository.save(user);
To find a User by ID, you can call the find() method:
User user = userRepository.find(1L);
To delete a User, you can call the delete() method:
userRepository.delete(1L);
Spring Boot JPA is quite friendly for developers as by using it they can use databases with ease in Spring Boot apps.
How does @Component differ from @Service and @Repository?
In Spring Boot, we use annotations to mark classes as beans. This allows Spring to automatically detect and manage these beans. There are several different annotations that we can use, depending on the purpose of the class.
here’s a concise comparison of @Component, @Service, and @Repository annotations in the context of the Spring Framework:
| Annotation | Purpose | Specialization | Example Usage |
|---|---|---|---|
@Component | Generic Spring bean marker | None | General-purpose beans |
@Service | Service class marker | Business logic layer | Service classes |
@Repository | Repository class marker | Data access layer | Data Access Object (DAO) classes |
In general, you should use the most specific annotation for your class. For example-
a) If your class provides business logic, you should use the @Service annotation in your code.
b) In case your class interacts with the database, the @Repository would be a better option.
c) On the other hand, if your class is a general Spring bean, it is best to use the @Component.
Next, we’ll see how to configure security using Spring Boot Security. Check security-related Spring Boot interview questions with answers.
What do you know about Spring Boot Security? How do you configure it?
Spring Boot Security is a framework that has a range of features for securing the application. These features include authentication, authorization, and session management.
To configure security for your SpringBoot application, you need to create a WebSecurityConfigurerAdapter class. This class comes with methods to tune up the security of your application.
For example, the following code shows how to configure basic authentication for your SpringBoot application:
public class MyWebSecurityConfigurerAdapter extends WebSecurityConfigurerAdapter {
@Override
protected void configure(HttpSecurity http) throws Exception {
http.authorizeRequests()
.anyRequest().authenticated()
.and()
.httpBasic();
}
}
Once you have created a WebSecurityConfigurerAdapter class, you need to register it with the framework. To do this, you can insert the following code to your application.properties file:
spring.security.web.configurer=com.example.MyWebSecurityConfigurerAdapter
Once you have registered the WebSecurityConfigurerAdapter class, Spring Boot will configure security for your application based on the methods that you have implemented in the class.
How does the Spring boot schedule tasks at specific intervals?
There are two ways to schedule tasks at specific intervals:
- Spring Boot Task Scheduler: Spring Boot provides a task scheduler to set up tasks at specific intervals. To use its task scheduler, you need to create a bean that implements the TaskScheduler interface.
- Spring Cron Expressions: Spring Boot supports cron expressions to set up tasks at specific intervals. To use cron expressions, you can add a @Scheduled annotation to a method in your SpringBoot application. The @Scheduled annotation specifies the cron expression for scheduling the task.
For example, the following code shows how to schedule a task to run every minute using the Spring-Boot task scheduler:
@Bean
public TaskScheduler taskScheduler() {
SimpleAsyncTaskScheduler taskScheduler = new SimpleAsyncTaskScheduler();
taskScheduler.setPoolSize(10);
return taskScheduler;
}
@Scheduled(fixedRate = 60000)
public void myTask() {
// Do something
}
For example, the following code shows how to schedule a task to run at 10:00 PM every day using a cron expression:
@Scheduled(cron = "0 0 22 * * *")
public void myTask() {
// Do something
}
What are Spring Boot Profiles, and how are they useful?
Spring Boot profiles are a way of managing configuration for different environments. For example, you might have one profile for development, one profile for testing, and one profile for production.
To create a profile, you can create a file with the .profile extension in the config directory of your classpath. For example, to create a development profile, you would create a file called development.profile in the config directory.
In the profile file, you can add properties that you want to configure for that profile. For example, the following code shows a development profile that configures the database connection URL:
spring.datasource.url=jdbc:postgresql://localhost:5432/my_database
To activate the profile, you can add the –spring.profiles.active=profile-name parameter to the command line when you start your application. For example, to activate the development profile, you would start your application with the following command:
java -jar my-app.jar --spring.profiles.active=development
You can also activate the profile using the environment variable SPRING_PROFILES_ACTIVE.
How do you customize the Spring Boot startup banner?
There are two ways to customize the Spring-Boot banner that is displayed during application startup:
- Using a text file: To customize the banner using a text file, create a file named banner.txt in the src/main/resources directory and paste the banner content into it.
- Using an image file: To modify the banner using an image file, create a file named banner.gif, banner.jpg, or banner.png in the src/main/resources directory.
Once you have created the banner file, start your SpringBoot application and the custom banner will be displayed during startup.
Learn how to write unit tests and integration tests. Check testing-related Spring Boot interview questions with answers.
How do you write unit tests in an app built using Spring Boot?
Spring Boot testing is a framework that provides different ways for testing Spring Boot apps. These features include JUnit integration, dependency injection, and mocking.
To write unit tests in Spring Boot, you can use its test annotation. It tells the framework to start the application in a test environment.
For example, the following code shows a unit test for the Spring application:
@SpringBootTest
public class MyControllerTest {
@Autowired
private MyController myController;
@Test
public void testGetUsers() {
List<User> users = myController.getAllUsers();
assertEquals(1, users.size());
}
}
When you run this test, Spring Boot will start the application in a test environment and inject the MyController bean into the MyControllerTest class. The test will then call the getAllUsers() method on the MyController bean and assert that the result contains 1 user.
Spring Boot testing is a powerful tool that has built-in support for testing the apps quickly and easily.
Summary: Spring Boot Interview Questions
These are just a few of the many questions that could be asked about Spring Boot. Spring Boot may host a lot of complexity inside, but it is also very easy to learn and use. If you are interested in learning more about Spring Boot, there are many resources available online and in libraries.
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