Spring Boot Interview Questions

In the IT world, the demand for Spring Boot is growing continuously because of its ability to make application development faster. If you are a Java developer and if you also know Spring Boot then you can expect excellent career growth. However, understanding technology alone doesn’t land you the desired job. What matters most is – your performance in the job interview.

Top 10 Frequently Asked Spring Boot Interview Questions

Spring Boot Interview Questions And Answers

1. What is the Spring Boot?

Spring Boot is used to developing stand-alone Java-based applications, which you can just execute. It is a module of Spring, which makes life easier for Java developers. 

2. What are the major advantages of Spring Boot?

Some of the major advantages of Spring Boot include the following:

• • • It is easier to create stand-alone and production-ready applications.
    • You can use Spring Boot with minimum configurations. You don’t need to have the entire Spring configuration set up.
    • It reduces application development time and increases productivity.
    • It eliminates the need for WAR files. Because it contains Tomcat and Servlet containers jetty.
    • It enables the development and testing of applications by providing the CLI tool.
    • It enables the monitoring and management of applications in development and production environments through its multiple APIs.

Related Article: Spring Boot Tutorial

3. When a Spring Boot application is executed as “Run as Java application”, what will happen in the background?

The tomcat server will be launched in the background.

4. How does Spring Boot function?

Based on the dependencies added to the project, Spring Boot automatically configures the application by using the @EnableAutoConfiguration annotation. Next, it scans all the components included in the project using the @ComponentScan annotation.

5. What purpose does Spring Boot Starter Actuator dependency serve?

The Spring Boot Starter Actuator dependency serves the purpose of monitoring and managing the application. Here is the code for it:

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6. What for Spring Boot Starter Security dependency is used?

The Spring Boot Starter Security dependency is used for the security of spring.

Here is its code: 

<dependency>

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

   <artifactId>spring-boot-starter-security</artifactId>

</dependency>

7. Which dependency is used for test case writing?

The Spring Boot Starter Test dependency is used for test case writing. Here is its code:

<dependency>

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

   <artifactId>spring-boot-starter-test</artifactId>

</dependency>

8. Which dependency is used in the creation of web applications?

The Spring Boot Starter Thyme Leaf dependency is used in the creation of web applications.

9. How do you create a Spring Boot application using Maven?

There are different approaches to create a Spring Boot application using maven. Here are they:

• Spring Boot CLI
• Spring Starter Project Wizard
• Spring Initializr
• Spring Maven Project

Also Read: Spring Boot vs Spring MVC: What is the Difference?

10. What is Spring Boot CLI?

You can create Spring Boot applications using the Spring Boot CLI. The Spring Boot CLI is a command-line tool. In the command prompt itself, you can create, run, and test the applications.

11. How do you create a Spring Boot project using Spring Initializr?

We can create a Spring Boot project using Spring Initializr by performing the below steps:

• Select the Maven project and the required dependencies.
• Enter Group, Artifact, and then click on Generate Project.

The project is downloaded.

• Extract the project into your system.
• Use the Import option on the Spring Tool Suite IDE to import the project.

Note: Make sure choosing the project type Maven and the source project has a pom.xml file during importing the project.

The Spring Boot project is created with all the required dependencies.

12. What for “@RequestMapping” annotation is used in Spring Boot?

The @RequestMapping annotation is used to provide routing information. It is also used to let Spring know that HTTP request, if any, has to be mapped to the corresponding method.

13. What for “@RestController” annotation is used in Spring Boot?

By using the @RestController annotation, we can add @ResponseBody and @Controller annotations to the class.

14. Which are the build systems supported in Spring Boot?

Maven and Gradle are the build systems recommended in Spring Boot because they support dependency management. 

15. Why for Spring Framework used in Spring Boot?

The Spring Framework is used for defining the beans and their dependency injection. You can use @ComponentScan annotation to find beans and the corresponding injection using @Autowired annotation.

16. What is the advantage of Spring Data?

Spring Data makes it easier to use cloud-based data services, relational databases, and non-relational databases. Ultimately, using Spring Data, data access becomes easier.

17. What purpose do Application Runner and Command-Line Runner serve in Spring Boot?

Both Application Runner and Command-Line Runner are interfaces. They are used to execute the code once the Spring Boot application is started.

18. What is the purpose of @Value Annotation in Spring Boot?

The purpose of @Value Annotation in Spring Boot is to read the value of the environment or application property in Java code. The following is the syntax for this:

	@Value("${property_key_name}")

19. What is an auto-configuration in Spring Boot?

The auto-configuration automatically configures the required beans and controllers, etc. thereby making the creation of Java application easier.

Related Article: What is Bean in Java Spring

20. How do you write a unit test for a Rest Controller file in Spring Boot?

In Spring Boot, we can create a web application context using SpringJUnit4ClassRunner and MockMvc and write a unit test for a Rest Controller file. 

Spring Boot Question And Answers For Experienced :

21. How do you handle the exceptions in Spring Boot?

In Spring Boot, we can handle the exceptions using the @ExceptionHandler annotation. To handle the exceptions globally, we need to use @ControllerAdvice annotation.

22. How do you create non-web applications in Spring Boot?

We can create non-web applications in Spring Boot by:

• Removing the web dependencies from the classpath.
• Altering the way Spring Boot creates the application context.

23. Which object is used to intercept the HTTP requests and responses of an application?

The filter object is used for this purpose. It facilitates performing two operations in two instances. Here are they:

• Before sending the request to the controller
• Before sending a response to the client

24. How do you connect an external database?

We can connect an external database using the steps mentioned below:

• Add dependency for the external database (for example, MySQL) Connector to pom.xml.
• Remove H2 Dependency from pom.xml.
• Set up the external database (for example, MySQL) and configure the connection to it.
• Restart the project.

25. How do you create applications, which consume RESTful Web Services?

We need to use the Rest template to create applications that consume RESTful Web Services.

------          Also Read: Microservices With Spring Boot          ------

26. What is the major advantage of the YAML file? How do you upload the YAML file to Spring Boot?

The major advantage of YAML is – it is easier to debug issues since data is stored in a hierarchical format. We can upload the YAML file to Spring Boot by using the methods mentioned below:

• To load YAML as a map - we need to use YamlMapFactoryBean
• To load YAML as properties - we need to use YamlPropertiesFactoryBean

27. What is a Thymeleaf template and what it is used in Spring Boot?

A Thymeleaf template is used to create web applications in Spring Boot. It is a Java-based library, which converts the files into well-formed XML files. Some of the template types it contains include - XML, Valid XML, XHTML, Valid XHTML, HTML5, and Legacy HTML5.

28. What is Cross-Origin Resource Sharing (CORS) in Spring Boot?

Cross-Origin Resource Sharing (CORS) is a security concept. It provides restriction of resources that are implemented in web browsers and also works in preventing the JavaScript code in producing/consuming the requests against another origin.

29. What purpose do RequestMapping and GetMapping methods serve in Spring Boot?

Both RequestMapping and GetMapping methods serve the same purpose of supporting consumes. The consume options include the following:

consumes = “text/plain”

consumes = {“text/plain”, “application/*”}

30. Which scheduler is used to execute the tasks at a specific time in Spring Boot?

To execute the tasks at a specific time, a Fixed Rate scheduler is used in Spring Boot. The Fixed Rate scheduler doesn’t wait for the previous task to be completed. Here is a sample code for this:

@Scheduled(fixed-rate = 1000)

public void fixedRateSch() {

}

31. What is the fundamental difference between a Fixed Rate scheduler and a Fixed Delay scheduler?

Both the Fixed Rate scheduler and Fixed Delay scheduler serve the same purpose of executing the tasks at specific times. However, the Fixed Rate scheduler doesn’t wait for the completion of the previous task whereas the Fixed Delay scheduler waits for the completion of it.

32. How do you configure the HTTPS and the port 443 in the Spring Boot application?

We can configure the HTTPS and the port 443 in the Spring Boot application:

• By getting the SSL certificate

Note: You can create a self-signed certificate. Alternatively, you can get it from a certificate authority.

• By enabling HTTPS and 443 port

33. How do you add a custom JS code to Spring Boot?

The custom JS code can be added to Spring Boot using the below steps:

• Under the Resources folder, create a folder and name it Static.
• In the newly created Static folder, place the static content.

34.  What purpose does the Spring Initializer serve in Spring Boot?

The Spring Initializer, which is a web application, enables the creation of the internal project structure. There is no need for manual setup.  

35.  Which component provides secured endpoints for monitoring and managing a Spring Boot application?

The Spring Boot Actuator serves this purpose. All endpoints of the actuator are secured by default. To enable the Spring Boot Actuator, We will require the addition of starter actuator dependency of spring boot in the build configuration file.

36. Which feature of Spring Boot ensures application security?

In the applications developed using Spring Boot, the logging and security feature ensures security.

37. How do you monitor and manage the applications in Spring Boot?

We can monitor and manage the applications in Spring Boot using the Spring Boot Admin Server. Though Spring Boot Actuator Endpoint can be used here,  if there are multiple applications, it cannot serve the purpose properly. This is because each application has separate actuator endpoints.

38.  What are the build support and servlet container support requirements for Spring Boot?

The following are the build support and servlet container support requirements for Spring Boot:

Build Support

• Maven 3.3+
• Gradle 4.4+

Servlet Container Support

• Tomcat 9.0 – Servlet Version 4.0
• Jetty 9.4 –  Servlet Version 3.1
• Undertow 2.0 – Servlet Version 4.0

39.  In Spring Boot, what is the process to be followed to change the Tomcat server port?

The Tomcat server port can be changed by following the steps mentioned below:

• In the Application Properties file, add a property of the server. port and assign it to any port.
• The application properties file loads automatically by Spring Boot and the required configurations apply to the application.

40.  Which RESTful web service is used to send an email with Gmail Transport Layer Security?

We need to use Spring Boot RESTful web service to send an email with Gmail Transport Layer Security.