♦ 11 Spring boot interview questions & answers

11 Spring boot interview questions & answers with tutorials for easy setup of new Spring applications. Spring boot helps you get started quickly.

Q1. What is the key benefit of using Spring boot?
A1. The key benefit is that you can “build a production ready application from scratch in a matter of minutes”.

Q2. How does spring boot enable you to “build a production ready application from scratch in a matter of minutes”?
A2. It takes the approach of “convention over configuration“.

1) The Spring jars dependency management and versioning are simplified as demonstrated in the spring boot example – Simple Spring Boot Tutorial in 8 steps

Spring Boot’s main benefit is its ability to configure resources based on what it finds in your classpath. If your Maven POM includes JPA dependencies and a PostgreSQL driver, then Spring Boot will setup a persistence unit based on PostgreSQL. If you’ve added a web dependency, then you get Spring MVC configured with sensible defaults.

2) Spring boot is based on an HTTP server. Spring Boot has an embedded version of Tomcat by default, but gives you a way to opt for Jetty server if you wish. This is demonstrated via Simple Spring Boot Restful Web Service Tutorial

Q3. How do you specify dependencies in Spring boot?
A3. Via spring-boot-starter-xxxxx.

Since “h2” database dependency is used, Spring boot will configure JPA persistence unit for H2 rather than the HSQLDB, which is the default. This approach is known as the “Opinionated Defaults Configuration

Q4. How will you get Spring boot to use Jetty server instead of Tomcat, which is the default?
A4. By adding the jetty server dependency “spring-boot-starter-jetty” in the pom.xml file.

Q5. What documentation would you be using to get started with your enterprise Spring boot application?
A5. “https://spring.io/docs” has lots of getting started guides [http://spring.io/guides] & tutorials.

Q6. What is Spring Boot CLI?
A6. CLI stands for Command Line Interface, which is a Spring Boot software to run and test Spring Boot applications from command prompt. When you run Spring Boot applications using CLI, then it internally uses Spring Boot Starter and Spring Boot AutoConfigurate components to resolve all dependencies and execute the application. It internally contains Groovy and Grape (JAR Dependency Manager) to add Spring Boot Defaults and resolve all dependencies automatically.

Q7. What are the different ways to generate a Spring boot project?

1) Using Maven as demonstrated in Simple Spring Boot Tutorial in 8 steps

2) Via online Spring Initializr – “http://start.spring.io/“. More info at “http://spring.io/”.

3) Via Spring Boot CLI.

4) Via Spring Boot IDE.

Q8 What is the difference between Spring IO & Spring Boot?
A8. Spring IO Platform is all about “list of dependencies and their versions that work well together”. It is implemented as a Maven POM file via Maven Bill-of-Materials dependency that you can import into your projects to set the versions for dependencies. Spring IO tutorial in 6 steps

Spring Boot is built on top of the “Spring IO” platform. Spring Boot makes it easy to create stand-alone, production-grade Spring applications that you can just run as covered in “Simple Spring Boot Tutorial in 8 steps” and Simple Spring Boot Restful Web Service Tutorial.

Q9 What are the key components of Spring Boot framework?
A9. Spring Boot has 4 key components.

1) Spring Boot Starter: is responsible for combining a group of common or related dependencies. E.g. spring-boot-starter-actuator, spring-boot-starter-web, spring-boot-starter-data-rest, spring-boot-starter-hateoas, spring-boot-starter-jdbc, spring-boot-starter-tomcat, etc.

2) Spring Boot AutoConfigurator: is responsible for simplifying the wiring up of Spring components. One of the common criticisms of Spring IO framework is that it requires lot of XML or Java based configurations. The Spring Boot AutoConfigurator component will take the burden of wiring up the Spring components. It also reduces the number of annotations. For example, @SpringBootAnnotation = @Configuration + @ComponentScan + @EnableAutoConfiguration.

3) Spring Boot CLI: is responsible for running & testing a Spring Boot application from a command prompt. It internally uses the components “Spring Boot Starters” and “Spring Boot AutoConfigurator”. You can also run Spring Web Applications from a command prompt.

4) Spring Boot Actuator: is responsible for providing production-ready features to a Spring Boot application without having to actually implement these things yourself. it exposes different types of information about the running application – health, metrics, info, env etc. This is not a replacement for a production-grade monitoring solution, but is a good starting point from a development & testing perspective.

Q10 How does Spring Boot work under the hood to simplify the build dependency & configuration?
A10. Spring Boot internally uses Groovy to tap into its features such as JAR dependency resolver engine (i.e. GRAPE) and default import statements.

Q11 What are the benefits of using Spring Boot in your next micro-service application?
A11. You can quickly build a stand-alone production ready application. It reduces lots of development time and increases the overall productivity due to

1) Lesser dependency management effort.

2) Lesser boiler plate code to wire up Spring components.

3) Easier to integrate within Spring ecosystems like spring-jdbc, spring-web, spring-orm, spring-data, spring-security, etc.

4) It follows “Opinionated Configuration Defaults” approach.

5) It provides embedded HTTP servers like Tomcat and Jetty to test your applications.

6) It provides lots of plugins to develop & test Spring applications with Maven & Gradle. For example, “spring-boot-maven-plugin” to create uber jars that can be deployed to a web server.

7) Spring Boot CLI tool helps to develop & test from a command line.

Spring boot key links

1. Spring Boot Web & Actuator Beginner Tutorial Step by Step.


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Arulkumaran Kumaraswamipillai
Mechanical Engineer to freelance Java developer within 3 years. Freelancing since 2003 for the major banks, telecoms, retail & government organizations. Attended 150+ Java job interviews, and most often got 3-6 job offers to choose from. Published Java/JEE books via Amazon.com in 2005, and sold 35K+ copies. Books are outdated and replaced with this online Java training. Join my LinkedIn group. 1,350+ paid memberships.

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