Spring Boot Interview Questions and Answers

Spring Boot Interview Questions and Answers

Are you willing to be a big expert and wish to prepare for the spring boot interviews? If your answer is yes, then below are the set of questions you need to prepare before you attend any interviews for spring boot concepts. The list of questions below are delicately tuned and prepared by highly practiced spring boot experts. The concepts explained and level of questions jotted down will give you a detailed overview of available concepts with spring boot. The wide range of questions given covers all the important topics that are frequently asked in the interview process. Some of the major concepts that these questions contain are IO platforms, AMQP, spring session, security, spring cloud, various spring framework and many. Java Full Stack Developers, Lead Architects, Java Architect are some of the professionals who can easily crack the interviews by going through the provided question and answers.

Best Spring Boot Interview Questions and Answers

In case you’re searching for Spring Boot Interview Questions and Answers for Experienced or Freshers, you are at the correct place. GangBoard offers Advanced Spring Boot Interview Questions and Answers that assist you in splitting your Spring Boot  interview and procure dream vocation as Spring Boot Developer. Below are some of the most important Spring Boot Interview Questions and Answers frequently asked to tech aspirants. Our advanced list of Spring Boot Interview Questions contains all the necessary information for both freshers and experienced job seekers to crack an interview and begin an auspicious career as a Spring Boot Developer.

Q1) What is Spring Boot?

Answer: Earlier, while working with huge enterprise computing softwares, developers had to focus both on the coding part and on the mass amount of configurations. Consequently, this resulted in a problem where developers could not dedicate the needful amount of time to coding. Therefore, Spring Boot came into picture. Spring Boot is an architecture built on top of the conventional spring framework. It allows developers to create deployment ready applications with configurations and linked jar files.
Below are the 4 key Spring Boot components:

• Spring Boot AutoConfigurator
• Spring Boot Starters
• Spring Boot Actuator
• Spring Boot CLI

Q2) Why do we need Spring Boot?

Answer: This is one of the most frequently asked Spring Boot Interview Questions and Answers that you must be aware about. While Spring framework provides developers with an ideal environment to build large applications, it often involves a number of jar files, configurations, server establishment, dispatcher servlet, component scan, view resolver, and much more, which results as a hindrance to the development.
Spring Boot is designed to relieve developers from this rattling problem. It provides with features such as starter projects where developers can find pre built projects for further development, auto configurations, etc., so that the application developers can focus on the conventions.

Q3) How is Spring Boot architecture? Is it the same as Spring MVC?

Answer: Although Spring Boot is built as an architecture to Spring framework, it is not the same as Spring MVC, nor is a substitution to the latter one.
In simple words, Spring Boot is a mediator that helps a developer to connect, configure, and develop more easily and efficiently with the Spring framework.
Some of the auto configuration files provided by Spring Boot are database config, security config, and security config, which saves essential development time. Moreover, there are features such as Spring Boot Starters, which cannot to found in Spring MVC.

Q4) What is Spring Boot Starters?

Answer: Moving ahead with the Spring Boot Interview Questions and Answers, it is important to know about Spring Boot Starters, which is one of the 4 major components of Spring Boot. To build a single application, there are a lot of dependencies in the Spring framework. Spring Boot Starter POMs are designed to reduce these dependencies into a single one.
Therefore, instead of going through a lot of data to find a sample code and copy the dependencies, Spring Boot Starters provides developers with a ready to use all in one set of dependencies.
Some of the Spring Boot Starters are Web Starter, Test Starter, Mail Starter, Data JPA Starter.
Jar dependencies can be added to Maven’s pom.xml or Gradle’s build.gradle file.

<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>1.4.0.RELEASE</version>
</parent>

Q5) What is Spring Boot AutoConfiguration, and why do we need AutoConfiguration?

Answer: Spring Boot autoconfigurator is one of the 4 key components of Spring Boot. It uses defined jar dependencies to automatically add configurations to your Spring MVC application.

@Configurationpublic class MySQLAutoconfiguration {
}
Further, a class is registered under org.springframework.boot.autoconfigure.
EnableAutoConfiguration key in the location resources/META-INF/spring.factories:
This class acts as an auto configuration candidate.
org.springframework.boot.autoconfigure.
EnableAutoConfiguration=\
com.training.springboot.autoconfiguration.
MySQLAutoconfiguration

Q6) What is Spring Boot CLI?

Answer: CLI stands for the Command Line Interface. Spring Boot CLI, as the name suggests, is used to begin quickly with the development using the Spring framework. Often, developers have to spend a lot of time after writing boilerplate code, which is nothing but a few lines of code that has to be included time by time with a little bit of modification.
Groovy scripts provided by Spring Boot CLI makers sure that app developers can spend time after conventional coding parts and business logic. Such a set up makes sure Spring application is developed and deployed more quickly and efficiently.

Q7) What is Spring Boot Actuator?

Answer: Once the application is deployed, Spring Boot Actuator allows you to bring production-ready features to it. Features for monitoring application, traffic patterns, metrics, health, env, and other operation-related insights are provided by the Spring Boot Actuator. It makes use of HTTP endpoints to enable the interaction, which can be extended further in multiple ways same as other components of Spring Boot.

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

Note: Regardless of the Spring Boot version, the above setup remains true just as specified in the BOM(Spring Boot Bill of Materials).

Q8) How to create a Spring Boot Project?

Answer: While facing Spring Boot Interview Questions and Answers, a candidate might be asked to create a simple Spring Boot project, which can be easily accomplished following below guideline or one may create a Spring Boot project following the guidelines provided on https://start.spring.io/

Folder Structure:

The main method is the heart of the Spring boot application to run the application.
@SpringBootApplication:
The @SpringBootApplication annotation is the same as using @EnableAutoConfiguration,

@Configuration, and @ComponentScan with default attributes.
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@SpringBootConfiguration
@EnableAutoConfiguration
@ComponentScan(excludeFilters = {
@Filter(type = FilterType.CUSTOM,
classes = TypeExcludeFilter.class),
@Filter(type = FilterType.CUSTOM,
classes = AutoConfigurationExcludeFilter.class) })
public @interface SpringBootApplication {
}

Q9) What is @Configuration and why is it needed?

Answer: @Configuration is a Spring annotation that is used to indicate @Bean method declaration by a class. It can be processed by Spring container in order to create service requests and bean definitions during runtime.
@Configuration is:
Required, only when the annotated class is defined in the @ComponentScan annotation but is not passed explicitly.
Not Required, if the annotated class is passed in the source parameters while calling SpringApplication.run().

Q10) What is @RestController annotation?

Answer: @RestController is a specialized controller that includes @ResponseBody and @controller annotations. @RestController is mainly used to simplify the controller implementation.

@RestController
public class HelloController {
@RequestMapping("/hello")
public String greeting() {
return"HelloWorld";
}
}

Q11) What is @RequestMapping annotation?

Answer: It is not unusual to be asked regarding various annotations while facing Spring Boot Interview Questions and Answers. However, do not hesitate and give your answer in simple terms using technical information such as below.
@RequestMapping is used to map class-level and method-level annotations.

• It maps class-level annotations with the controller in the requested pattern or path.
• Further, @RequestMapping specifies mappings to handler methods with method-level annotations.

Q12) What is @RequestBody annotation?

Answer: @RequestBody annotation is used to bind a method parameter to incoming HTTP requests with the mentioned URL in @RequestMapping annotation.
Here, HTTP message convertors are used to map HttpRequest body to a domain object, which consequently helps to automatically deserialize the body to a Java object based on header present in the request.

Q13) What is @ResponseBody annotation?

Answer: The task of @ResponseBody annotations is to inform the controller that the returned object has been serialized into Json, the returned value will be bound to HttpResponse body.
Here, Spring HTTP message converters serialize the return value to the type specified in HTTP header.

Q14) What is @ResponseEntity annotation?

Answer: @ResponseEntity, as the name suggests, is an annotation that represents the HTTP response entity. @ResponseEntity contains constructors that allow you to specify status code, body, header, and other information.

Q15) What is @pathVariable?

Answer: @PathVariable annotation is used to directly extract information from the URI.

Q16) What is MediaType?

Answer: MediaType is used to specify the type of data that is to be produced or consumed by the controller. This narrows down and aids with mapping.

Q17) What is REST API?

Answer: Restful API is one of the favorite Spring Boot Interview Questions and Answers of recruiters to interrogate a fresher candidate.
REST API or RESTful API is used to transfer HTTP requests such as Get, Post, Put, and Delete. REST or Representational Transfer is a technology that imitates the communication style used for web services.

Q18) What are the types of HTTP methods and Corresponding RestTemplate methods?

Answer:
GET: Read operations
Use: To retrieve the list of customers and use sorting, pagination, and filtering to navigate big lists.
Status codes: 200 – (OK) valid request, 404 – (Not Found) Invalid request.
POST: Location header with link to /customers/{id} containing new ID
Use: To create the newrecord with new id.
Status codes: 201 (Created), 404 (Not Found), 409 (Conflict) if resource already exists.
PUT: To update/replace every resource in the entire collection.
Use: To update/replace data
Status codes: 405 (Method Not Allowed), 200 (OK), or 204 (No Content), 404 (Not Found), in case of ID invalid or not found.
PATCH: unless you want to modify the collection itself.
Use: To update/modify data
Status codes: 405 (Method Not Allowed), 200 (OK), or 204 (No Content), 404 (Not Found), in case of ID invalid or not found.
DELETE: To completely delete the collection – often not desirable
Use: To perform deletion
Status codes: 405 (Method Not Allowed), 200 (OK), or 204 (No Content), 404 (Not Found), in case of ID invalid or not found.

Q19) Difference between POST and PUT methods?

Answer: Basically, Put is used to replace all the target resources with the selected/requested payload. On the other hand, Post method is used to submit or send data to the specific server or resource such as file upload, information, or changing the current status.
An explicitly created object suggest use of the Put method while server-specified name shows the use of Post method.
Put allows you to Put objects more than a single time and also allows creation or updation of resources using the exact object or URL.
On the other hand, Post allows multiple requests at the same time to make changes to an object or URL.

Q20) What is @Autowired annotation and its usage?

Answer: Same as the @Required annotation, @Autowired annotation can be used to bind or autowire bean with the setter method. In other words, one can implicitly define object dependency. It provides developers with control regarding autowiring.

Q21) How many ways the autowired can mode?

Answer:

• No: It’s the default option. Defining not to auto-wire, which is set using ref attribute.
• byName: This makes use of property name for auto wiring. If bean name matches other bean property name, auto wiring is done.
• byType: Same way as the byName mode, if the bean data type is shown to be compatible with other bean property, auto wiring is done.
• Constructor: byType mode defined in the constructor.
• Autodetect: Finds the default constructor for auto wiring. If not found, byType autowiring is performed.

Q22) What are the limitations of autowiring mode?

Answer:

• If the constructor contains explicit dependencies, they will override autowiring instructions.
• Possibilities of Overriding: Dependencies can be easily defined using constructor-arg or property tags to override the auto wiring.
• String, integer, and similar data type properties have to be defined manually and cannot be autowired.

Q23) What is spring-boot-starter-data-jpa?

Answer: Spring Boot provides spring-boot-starter-data-jpa, which is one of the Spring Boot Starters, to easily connect relational database with Spring MVC applications.

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

Q24) How does JPA Work?

Answer: JPA stands for Java Persistence API, which is used as an API that allows the developers to work with objects. When you deal with a relational database, you have to make use of SQL statements in order to retrieve information for certain queries. JPA eliminates the need of using SQL statements and allows the developers to deal with objects without SQL statement requisite. Developers can perform actions such as accessing, modifying, managing, and persisting information.
A JPA persistence provider can create a database schema by following the information provided in metadata. Here, JPA metadata has to be defined in the Java class. Metadata can also be defined using XML. JPA can handle both static and dynamic object-based queries.

Q25) What is the difference between JPA and Hibernate?

Answer: While JPA and Hibernate both are completely different entities, they are interconnected in certain ways. JPA is an API that provides developers with specifications and guidelines for implementation. However, it is not implementation and will require a tool that can implement the specifications.
Consequently, Hibernate comes into picture, which is nothing but a tool that follows the guideline as well as compulsory and optional specifications defined by JPA and makes it functional.
Using Hibernate for JPA implementation also allows you to switch over other implementation tools easily, which is not possible if used Hibernate alone.

Q26) What is the spring-boot-starter-test?

Answer: Spring-boot-starter-test is the dedicated testing module of the Spring Boot. It brings the Starter Test Modules and a certain number of libraries to test your application.
Following is the list of libraries in the Spring-boot-starter-test module:

• Hamcrest
• JsonPath
• JUnit
• AssertJ
• Mockito
• Spring Test & Spring Boot Test
• JSONassert

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

Q27) How to test the Controller class in Spring Boot?

Answer: To test the controller class in Spring Boot, developers have the following 2 alternatives:

• To use the mock environment or
• To use an embedded Servlet container.

Q28) What is @RunWith(SpringJUnit4ClassRunner.class)?

@RunWith is an annotation used to define if a class should run along a specific runner class. SpringJUnit4ClassRunner.class is used as Spring Boot makes use of the Spring test. A developer can choose from multiple of runners based on the test.

Q29) What is @ContextConfiguration annotation?

Answer: In order to configure ApplicationContext for tests such as integration, @ContextConfiguration annotation is used. It shows the ApplicationContext resource and classes utilized to load it.
@ContextConfiguration calls ClassPathContextConfiguration, which helps to identify the Java classes and ContextLoader to run on JVM.
Same way, AnnotationConfigContextLoader.class is a ContextLoader used to determine the classes to load.
If you are asked to provide an example for @ContextConfiguration during Spring Boot Interview Questions and Answers, use the below code.
A simple example for the @ContextConfiguration annotation:

@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration(classes = Sample.class,
loader = AnnotationConfigContextLoader.class)
public class JUnitSpringExample {}
Class file:
@Configuration
public class Sample {
@Bean
public SampleService getSampleService() {
return new SampleServiceImpl();
}}

Q30) What is Swagger2?

Answer: Swagger is used to describing the structure of APIs. Swagger 2 is an open-source service provided in Spring Boot that makes it easier for the machines to identify the structure of APIs such as RESTful Web services.

<dependency>
<groupId>io.springfox</groupId>
<artifactId>springfox-swagger2</artifactId>
<version>2.9.2</version>
</dependency>

Q31) How to integrate the Swagger2?

Answer: Below is a sample for the integration of Swagger2 with docket:

@Configuration
@EnableSwagger2
public class SwaggerConfig {
@Bean
public Docket api() {
return new Docket(DocumentationType.SWAGGER_2)
.select()
.apis(RequestHandlerSelectors.any())
.paths(PathSelectors.any())
.build();
}
}

@EnableSwagger2 annotation is used to enable Swagger 2.
Once Docket bean is specified, the select method returns an ApiSelectorBuilder instance. This instance is used to determine how to control the exposed endpoints.
RequestHandlerSelectors and PathSelectors are used to configure predicates for of RequestHandler selection. Lastly, any() method will facilitate the documentation using Swagger.
The above configuration can be used to integrate Swagger2 with a Spring Boot Application.

Q32) What are the advantages or features of Spring boot?

Answer: Below are listed features and advantages of Spring boot Starter dependency and In built-in configuration – This feature provides common dependencies and it helps to improve productivity.
Auto-Configuration –
This is one of the best features in Spring Boot Which helps to write loosely coupled code. To develop Web Application Spring boot contains Spring web application and Thymeleaf on the classpath so it can configure automatically template resolver and other settings.
Spring Initializer – Initial project structure can be done with Spring boot in a very simplified way.
Spring Actuator –  This feature also very useful to find out beans creation in the Spring application context and request mapping with a controller.
Spring CLI – This is also one of the good features of Spring boot which makes spring boot development to reach the next level and it’s allowed to concise code.

Q33) What is Spring Boot Starter in Spring Boot Framework?

Answer: This is just Spring Boot Starters JAR Files. It’s used for auto dependency resolution.

Q34) What is AutoConfigurator in Spring Boot Framework?

Answer: This Framework contains AutoConfigurator Which is used to provide Auto-Configuration.

Q35) What is the Actuator in Spring Boot Framework?

Answer: Spring Boot Framework used Actuator which provides to see the health of the application and EndPoints information internally.

Q36) How Spring Boot Application runs on custom Port?

Answer: You can change the port in application.properties to run the application on a custom port.
server.port = 8090

Q37) How to spring security embedded with Spring Boot?

Answer: We have to add spring security starter in the boot application
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-security</artifactId>
</dependency>

Q38) What are the in build containers Which work with Spring Boot?

Answer: Tomcat, undertow, and jetty server are embedded with the Spring boot.

Q39) How custom JS embedded with Spring Boot?

Answer: As per project standard, We can create a package that will contain static content.
resources/static/javaScript/App.js
Above one can be referred to JSP like below
<script src=”/javaScript/App.js”></script>

Q40) Transaction start on which layer?

Answer: Basically recommendation to use this in the service layer and if there are a number of transaction which are part business it should rely on the business or service layer.

Q41) What is the use to maintain profile in Spring boot?

Answer: Most of the Enterprise application development is required in multiple environments to complete the development and testing of the same. Profile help to main multiple environments configuration.
Development
Integration Environment
UAT Environment
Pre-Production Environment
Production Environment

Q42) How to write Test cases using Spring Boot?

Answer: @SpringBootTest annotation used for writing test cases in Spring boot.

Q43) What is YAML?

Answer: This is a configuration file and it’s human-readable. The YAML file is much structured and looks easy to understand the configuration, It contains hierarchical configuration data.

Q44) How Exception Handling implement using Spring Boot?

Answer: Spring boot has a very useful way to do this. ControllerAdvice used to handle exceptions in Spring Boot. This will be implemented everywhere where it handles all exceptions thrown by the controller class.

Q45) What is @SpringBootApplication in Spring Boot?

Answer: This annotation is equal to @ComponentScan, @Configuration, @EnableAutoConfiguration.

Q46) How we can run spring boot application in debug mode?

Answer: Need the executions of below
Java -jar my App-0.0.9-SNAPSHOT.jar –debug

Q47) How JSON REST service implemented in spring boot?

Answer: @RestController annotation used to implement and spring application render default JSON response as Jackson is on the classpath.

Q48) How an application can be shut down with an actuator?

Answer: The application can be shut down properly with the shutdown endpoint configuration. By default it is disabled. It can be enabled in application.properties.

Q49) What is docker in Spring Boot?

Answer: This is a tool that is used to create, deploy, run a project by using containers.

Q50) What is an aspect?

Answer: This is required for cross-cutting requirements.

Q51) What are the Spring Boot Starters, list out some of them?

Answer: Below is the starters in Spring Boot.
Freemarker
web
Security
Thymeleaf
Parent

Q52) What is Spring Boot?

Answer: Spring boot is a web software framework primarily based on Java.
Spring boot is a module of Spring affords equipment and libraries to create a custom-designed web application
Spring boot to create a Spring application task that could just run/ execute
Spring is greater complicated than Spring Boot
Spring Boot is less complex than the Spring framework.

Q53) what happens in the background when a Spring Boot Application is executed as “Run as Java Application”?

Answer: while a Spring Boot app is executed as “Run as Java Application, then it routinely launches up the tomcat server and deploys the application automatically.

Q54) Mention the requirements for a Spring boot application?

Answer: For Spring Boot 2.1.7.RELEASE requires
Java 8 and above
Spring Framework 5.1.9 above
Build tools:
Maven 3.3 above
Gradle 4.4 above
Servlet Container:
Tomcat 9.0 – Servlet Version 4.0
Jetty 9.4 –  Servlet Version 3.1
Undertow 2.0 – Servlet Version 4.0

Q55) How to enable HTTP/2 support in Spring Boot

Answer: you may allow the HTTP/2 assist in Spring Boot by way of server.http2.enabled=true

Q56) From which layer transaction starts in SpringBoot?

Answer: The transaction starts from Service Layer as the implementation for the business is present in the service layer itself.

Q57) H2 database configured by Spring Boot is called?

Answer: The default H2 database: testdb.
In the Configuration file:
spring.datasource.name=testdb

Q58) List out the features of Spring Boot?

Answer: Few are the important features in Spring Boot
Spring initializer
Starter dependency
Auto-configuration

Q59) Is it possible to use Spring Boot with an application not having Spring?

Answer: It’s not possible as it’s work or limited to Spring apps.

Q60) @pathVariable What is the use of this annotation in spring boot?

Answer: This annotation helps to extract information from the given path variable URI.