Most Asked Spring Boot Interview Questions and Answers

Spring boot is one of the prime topics of discussion in most IT job interviews, especially when it comes to developing Java applications. Due to its fast, low configuration, inbuilt server, and self-monitoring features, spring boot helps create independent java-based applications with a robust and maintainable structure.

This write-up will take you through all the spring boot questions, both for fresher and advanced-level interviews.

What is spring boot?

Spring boot is a Java-based framework primarily used for building independent microservices or Rapid Application Development. It comes with added auto-configuration support and embedded servers for Jetty and Tomcat applications.

Technically speaking, spring boot refers to a micro open-source framework maintained by an enterprise – Pivotal. This framework is a platform for Java developers to create production-grade and auto-configurable spring applications. Java developers using spring boot can efficiently prepare and configure all their spring applications.  

What makes spring boot unique?

Spring boot stands out  from its other counterparts because:

  • It helps develop standalone spring applications with minimum configuration needs.
  • It offers starter dependencies to streamline and simplify the build configuration.
  • It allows you to embed Jetty, Tomcat, etc., without deploying WAR files.
  • It includes many production-ready features, including health checks, metrics, and external configuration systems.

What has popularised spring boot to such a great extent? 

Spring boot uses Java, one of the most sought-after programming languages loved by developers worldwide. It is an excellent tool that helps Java developers run and maintain enterprise-grade apps without worrying about configuration requirements and safety checks. Also, the spring boot community is expansive and highly resourceful. The readily accessible information about this framework further helps boost its popularity. 

Additionally, using spring boot gives you other benefits like:

  • It decreases development time while escalating the development team’s productivity.
  • It includes an auto-configuration feature for all components for designing production-grade applications.
  • It has a default setup for integration and unit tests, making it a solid platform for Java developers.
  • It doesn’t require numerous boilerplate codes, XML configurations, or annotations. 
  • It has an embedded HTTP server like Jetty to test web-based applications.
  • It includes various plugins to enable developers to work smoothly in memory and embedded databases. 
  • It allows users to quickly connect with queue services and databases like Oracle, MySQL, PostgreSQL, ActiveMQ, MongoDB, Solr, Redis, Rabbit MQ, etc.

Top spring boot interview questions – Freshers

Here are some of the most popularly asked questions for spring boot fresher level interviews:

1. Mention the advantages of creating apps through spring boot?

Ans. The significant advantages of using spring boot for app development are:

  • Very simple to understand while developing spring-based applications.
  • It is an already existing framework with an embedded annotation configuration and an HTTP server. These two aspects make it easy to understand.
  • It improves productivity while decreasing the development time.
  • It requires minimal configuration.
  • Users need not write any XML configuration, apart from some design-related parts.

2. Can you tell us about the critical components of spring boot?

Ans. The essential components of spring boot are:

  • Auto-configuration setup of spring boot
  • Starter spring boot POMs
  • CLI spring boot
  • Spring boot actuator framework

3. Why do Java developers prefer using spring boot over spring?

Ans. Most java developers indeed prefer using spring boot over spring. This is so because of the following features:

  • Version management
  • Starter POM
  • Auto configuration
  • Embedded server
  • Actuators
  • Component scanning
  • InMemory DB.

4. What are the different starter dependency modules of spring boot?

Ans. The most frequently used starter dependency tools are:

  • Test starter
  • Data JPA tool
  • Security starter
  • Mail starter
  • Web starter
  • Thymeleaf starter

5. Can you tell us how exactly Spring Boot works?

Ans. Spring boot framework automatically configures the application based on the dependencies input by the Java developer to the application project and annotation configuration. The starting point of any spring boot application contains “@SpringBootApplication” configuration annotation along with the main methodology.

Spring Boot also automatically scans all the project components with “@ComponentScan annotation.

6. Can you tell us what the annotation of @SpringBootApplication does internally?

Ans. The annotation of “@SpringBootApplication” is the same as using “@Configuration, @EnableAutoConfiguration,” and “@ComponentScan” along with all the default attributes of these annotations. Spring boot framework allows Java developers to use a single annotation rather than multiple ones.

7. What’s the purpose of using @ComponentScan annotation in the class file?

Ans. The spring boot framework scans all the package declarations and beans upon the initialization of the application. After this, we need to embed the @ComponentScan configuration annotation. This will allow the class files to scan all components added to the project.

Top spring boot interview questions – Advanced

Here are some popular questions asked in a Spring Boot professional level interview:

1. How would it be possible to override all the default properties within any Spring boot application?

Ans. Spring boot provides multiple properties that can be overwritten. You can do this by specifying the changes within the application properties. For instance, if you need to specify any prefix or suffix in a Spring MVC application, you can do it by embedding the following properties within the application.properties file:

  • “spring.mvc.view.suffix:”
  • “.jsspring.mvc.view.prefix: /WEB-INF/”

2. How would you run a Spring boot application on a custom port?

Ans. To run a spring boot application in a custom port, you only need to put the server. port features within the application properties. For example:

server.port=8050″

3. Why have you opted for spring boot modules in your java applications?

Ans. Using spring boot modules makes it simpler for us to create Spring-based applications. This helps you save significant time and effort. 

Let’s say you want to develop a spring boot project by using an ActiveMQ. For this, you can simply embed “spring–boot–starter–activemq” as an artifact code. It will automatically take the defaults by creating ActivemQ based spring application. 

However, let’s assume you don’t want to use an inbuilt ActiveMQ. Here, you can simply override “spring.activemq.broker-URL” within the application_properties to use an external ActiveMQ.

4. Tell us about the use of DevTools in modules of Spring boot?

Ans. Spring boot comes with embedded DevTools, which increases the overall productivity of developers. The most significant advantage of DevTools is that you need not redeploy the application each time you make a change. Usually, developers can just reload the respective changes without restarting the server. This avoids the pain of redeploying applications every single time a change occurs. 

5. What do you mean by an actuator in modules of spring boot?

Ans. A spring boot actuator is the most crucial feature of a spring boot. It is used to access the current form of running applications in the production environment. Additionally, you can use several metrics to check the current state of the java application.

Spring boot actuators provide smooth web services with endpoints that can simply check the required metrics. For example, the “/metrics:” endpoint shows metrics like processors, free memory, uptime, and other properties.

This way, the spring boot actuator lets developers monitor the application in the production environment. These RESTful endpoints are pretty sensitive, meaning they offer restricted access exclusively to authenticated users. However, you can override the in-app.properties to change this feature.

6. How will you be able to implement the Spring security system in any Spring boot-based application?

Ans. Implementing spring security in any spring boot application one requires minimal configuration. You just need to enter the spring-boot-starter-security-starter in the pom.xml. After this, you must input a configure class that will extend to the WebSecurityConfigurerAdapter by overriding all methods to achieve the required security in any Spring boot application.

7. Tell us about the difference between @Controller and @RestController in a Spring Boot module?

Ans. The @RestController model simply returns the objects as well as the object data. Both these are directly written using HTTP response as XML or JSON.

On the other hand, the @Controller Map of the spring boot model allows one to view the project in a template form and make it readable for humans.

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Conclusion

Spring boot is a trendy and necessary add-on for Java developers. Today, many software development job posts demand developers to possess spring boot knowledge. After all, it makes Java-based app development an easy and hassle-free affair. Whether you’re a fresher or an experienced developer, being well-versed with the nitty-gritty of spring boot will give you an upper hand over your competitors.

Can spring boot be used with non-spring applications?

No, this isn't possible because spring boot is strictly limited to all Spring-based applications only.

Is spring boot used to develop only REST APIs?

No, spring boot isn't only for REST-based APIs. It instead is an autoconfiguration mechanism for Java-based apps. Hence, you can use it for both the back-end and front-end.

What are the disadvantages of Spring boot?

The major disadvantages are:

1. While it’s excellent for microservices, it is unsuitable for large-scale projects.
2. It is pretty time-consuming to convert a legacy app or an existing Spring project into a spring boot app.
3. It often leads to numerous unnecessary dependencies, increasing the size of the deployment file.

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