Spring Boot Interview Questions, Study notes of Architecture

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Quick Reference

• Q1. What is the Spring Boot?
• Q2. What are the advantages of Spring Boot?
• Q3. What are the different Spring Boot Components?
• Q4. What are Spring Boot Starters?
• Q5. Name some of the starter provided by Spring Boot?..................................................................................................
• Q6. What is Auto-Configuration in Spring Boot?
• Q7. Can we use Spring Boot for non-Spring application?
• Q8. What are the different options for creating the Spring Boot application
• Q9. What is the Spring Boot Initilizr?
• Q10. What are the advantages of Spring Boot Initializr?
• Q11. How can I reload my Spring Boot changes without restarting the server?
• Q12.What are the embedded containers supported by Spring Boot?
• Q13. What is the Spring Boot Actuator?...................................................................................................................................
• Q14. How to run Spring Boot application to custom port?
• Q16. How can we create a custom endpoint in Spring Boot Actuator?
• Q17. What logging support provided by Spring Boot? How can we control logging level in Spring Boot?
• Q18. How to implement security for Spring boot application?
• Q19. How to configure database using Spring Boot?
• Q20. How can we use Jetty instead of tomcat in our web application?
• Q21. Why do we need spring-boot-maven-plugin?
• Q22. How to disable specific auto-configuration in spring boot?
• Q23. What is the use of YAML in Spring Boot?
• Q24. What is new in Spring Boot 2.0?
• Q25. What is @SpringBootApplication annotation?
• Q26. How to include custom static content in Spring Boot application (e.g custom JS code)?
• Q27. How to use a profile with Spring Boot?........................................................................................................................
• Q28. How to generate a WAR file with Spring Boot?

Q3. What are the different Spring Boot Components?

1. Boot Initializer
2. Spring Boot Starter
3. Auto Configurator.
4. Spring Boot CLI.
5. Actuator.

Q4. What are Spring Boot Starters?

Spring Boot Starters are the set of convenient dependency descriptors which can

be easily included in any level of application. These starters work as a

bootstrapping process for the Spring related technologies, we no longer need to

worry about the dependencies and they will be automatically managed by

Spring Boot Starters.

The starters contain a lot of the dependencies that you need to get a project up

and running quickly and with a consistent, supported a set of managed transitive

dependencies. To summarize, Spring Boot Starters are just JAR files used by

Spring Boot for auto-dependency.

Read Spring Boot Starters for more detail.

Q5. Name some of the starter 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

For a complete list, read Spring Boot Starters List

Q6. What is Auto-Configuration in Spring Boot?

It takes a lot of configurations and boilerplate code create a simple Spring MVC

application without Spring Boot_._ Spring Boot Auto Configuration provides an

opinionated approach to bootstrap your application. Auto-Configuration will

attempt to automatically try to set up our application with default behaviour

based on the jars in the classpath.

For example, if Spring Boot finds HSQLDB in our classpath, it will automatically

configure an in-memory database for us. Think of the auto-configuration as an

intelligent system which can provide ready to use the application to us based on

the configured jars in our classpath. For detail information please read our

article Spring Boot Auto Configuration

Q10. What are the advantages of Spring Boot Initializr?

Spring Boot Initializr provides a simple interface to quickly bootstrap a Spring

Boot application. Here are some of the benefits or advantages of using Initilizr.

● Spring Initializr provides an extensible API to generate quick start projects. ● Reduce time to create an application setup. Application setup can be created using a few clicks. ● It increases Productivity ● Initializr offers a configuration structure to define all the aspects related to the project to generate: list of dependencies, supported java and boot versions.

Q11. How can I reload my Spring Boot changes without

restarting the server?

This is achievable by Spring Boot Dev Tools module. It’s a powerful tool for

development. It helps developers to shorten the development cycle and enable

easy deployment and testing during development.

To enable this feature, add the following dependency to the Maven POM file.

org.springframework.boot spring-boot-devtools

Read Spring Boot Dev Tools for different features of Dev Tools.

Q12.What are the embedded containers supported by Spring

Boot?

Spring Boot includes support for the following embedded containers

1. Tomcat
2. Jetty
3. Undertow.

Use the right “Starter” to configure the embedded container.

Q13. What is the Spring Boot Actuator?

The actuator provides production-ready features for Spring Boot application. It

will help us to check and manage our application in the production environment.

We don’t need any code to get these features since they are available once the

actuator dependency is in the class-path. The actuator provides features like

auditing, health, metrics, environment information, thread dump etc. using

HTTP endpoints. Read Spring Boot Actuator for more detail.

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

Use the application.properties file to configure a custom port for Spring Boot

application. To change the server port, use server.port property.

server.port= 9001

Read Spring Boot Web Application Configuration for more detail.

Q1 6. How can we create a custom endpoint in Spring Boot

Actuator?

To create a custom endpoint using Spring Boot 1.x, we should expose the

instance of the custom endpoint class as a bean. We need to implement

Endpoint interface.

@Component public class CustomEndpoint implements Endpoint { //methodimplimentation }

Spring Boot 2.x changed it completely by introducing @Endpoint annotation.

Spring Boot expose endpoints with @Endpoint, @WebEndpointor and

@WebEndpointExtension over HTTP using Jersey, Spring MVC, or Spring Web

Flux. Read Custom Endpoint in Spring Boot Actuator for more detail.

Q17. What logging support provided by Spring Boot? How

can we control logging level in Spring Boot?

Spring Boot provides options to use all popular logging API using the relevant

starter, by default Spring Boot use Commons Logging for its internal logging. If

we are using Spring Boot Starters for our application, Logback will be used for

logging by default unless we want to use any other logging API. To use any other

logging API, we need to add the correct starter in our application. In case we like

to use Log4j2 for logging configuration, all you have to add the log4j2 starter in

your application (You may have to exclude Logback using pom.xml file).

Spring Boot provides an easy way to configure and set logging levels for your

application. We can use application.properties file to configure the desired

Logging level for our application by using ‘logging.level.*=LEVEL’. Here is an

example for the same. Read Spring Boot Logging for more detail.

logging.level.com.javadevjournal.rest=WARN

Q18. How to implement security for Spring boot

application?

Use the spring-boot-starter-security starter to enable the Spring security

support in your Spring Boot application.

< dependency > < groupId >org.springframework.boot</ groupId > < artifactId >spring-boot-starter-security</ artifactId > </ dependency >

Q19. How to configure database using Spring Boot?

The Spring Framework provides extensive support for working with SQL

databases, from direct JDBC access using JdbcTemplate to complete “object-

relational mapping” technologies such as Hibernate. To connect configure the

database for your Spring Boot application, use the spring-boot-starter-jdbc or

spring-boot-starter-data-jpa starters. For datasource configuration, use the

application.properties file in your application.

spring.datasource.url = jdbc:mysql://localhost/javadevjournal spring.datasource.username = root spring.datasource.password = spring.datasource.driver-class-name = com.mysql.jdbc.Driver

Above example is to configure MySQL in your application. For more information

read Configuring MySQL for Spring Boot Application

Q21. Why do we need spring-boot-maven-plugin?

Spring Boot Maven plugin provides Spring Boot support in maven. This plugin

provides options to create an executable jar or war files. Here are some of the

goals for this plugin.

● boot: run runs your Spring Boot application. ● spring-boot:repackage repackages your jar/war to be executable. ● spring-boot:start and spring-boot:stop to manage the lifecycle of your Spring Boot application (i.e. for integration tests). ● spring-boot:build-info generates build information that can be used by the Actuator.

To include this plugin in your project, add XML in the plugins section of your

pom.xml

< plugins > < plugin > < groupId >org.springframework.boot</ groupId > < artifactId >spring-boot-maven-plugin</ artifactId > < version >2.0.5.RELEASE</ version > < executions > < execution > < goals > < goal >repackage</ goal > </ goals > </ execution > </ executions > </ plugin > </ plugins >

Q22. How to disable specific auto-configuration in spring

boot?

To exclude specific auto-configuration classes, use the exclude attribute of

@EnableAutoConfiguration to disable them. Here is a sample code for the same.

@Configuration @EnableAutoConfiguration(exclude={DataSourceAutoConfiguration. class }) public class CustomConfiguration { }

Q23. What is the use of YAML in Spring Boot?

YAML is a superset of JSON.Spring Boot YAML as an alternative to the

application.properties file to define your project properties. The

SpringApplication class automatically supports YAML as an alternative to

properties whenever you have the SnakeYAML library on your classpath.

Let’s take the following example of the application.properties file.

environments.dev.url = https://dev.javadevjournal.com environments.dev.name = Developer Setup

This can be represented in the YAML files as follows.

environments: dev: url: 'https://dev.javadevjournal.com' name: 'Developer Setup'

Q25. What is @SpringBootApplication annotation?

This is one of the most important and core annotations from Spring Boot. We

use this annotation to mark the main class of our Spring Boot application.

@SpringBootApplication public class SpringOrderAnnotationApplication { public static void main(String[] args) { SpringApplication.run(SpringOrderAnnotationApplication. class , args); } }

@SpringBootApplication is a convenience annotation that is equal to

declaring @Configuration, @EnableAutoConfigurationand

@ComponentScan with their default attributes.

You have the option to use @Configuration,

@EnableAutoConfiguration, and @ComponentScan individually but the

recommendation is to @SpringBootApplication annotation. For more

detail, please read Spring Boot Annotations.

Q26. How to include custom static content in Spring

Boot application (e.g. custom JS code)?

Spring Boot search specific location in the project for serving static contents. By

default, Spring Boot serves static content from a directory called /static (or

/public or /resources or /META-INF/resources) in the classpath or

from the root of the ServletContext.

We can put our custom static content in any of the above folders. For example,

put the custom.js file under /resources/static/custom.js. To refer to

this file in the view, simply use the following code

Q27. How to use a profile with Spring Boot?

Spring Boot provides multiple ways to active profile. We can pass profile

information through the command line or use application.properties,

Spring Boot also provide a way to set profile programmatically.

Use profile specific configuration files in out Spring Boot application. We need

to the naming convention of application-{profile}.properties where

the profile defines the name of the intended profile. Profile specific files will be

loaded from the same location as application.properties file. Read

Introduction to Spring Profiles Using Spring Boot for more detail.

Q28. How to generate a WAR file with Spring Boot?

We can control the package type generation in our Spring Boot project using

spring-boot-maven-plugin to build a war file, we need to follow these 2

steps.

1. Set the packaging type as a war in our pom.xml file.
2. Mark the embedded container dependencies as “ provided ” (To build a war file that is both executable and deployable into an external container.)

Here is a snapshot from pom.xml