Are you a Java Spring Boot developer looking forward to acing an upcoming interview but are not sure what questions to expect? We are here to help!

This article will help you adequately prepare by outlining several frequently asked Spring Boot interview questions and answers that interviewers can use to test you.

Interviewers use strategic Java Spring Boot questions to test the interviewees’ skill levels relevant to their designated role. Therefore, you need to prepare with relevant questions and know how to answer them.

Before jumping right to the interview questions and their corresponding answers, let us cover a basic overview of what Spring Boot is and how helpful it is for Java developers.

What is Java Spring Boot?

This Java framework is a creation by the pivotal team in 2014. Spring Boot, which is an open-source framework, efficiently develops applications that are independent, production-grade, and can also run on a Java Virtual Machine(JVM).

Java developers prefer it for web applications and microservices development for its fast and easy setup process and safe configuration time.

The easy setup and configuration of the Spring-based applications by Spring Boot are possible with its three core capabilities which include:

  • Autoconfiguration – which is an automatic configuration of the Spring application.
  • Spring Boot provides an opinionated approach to the configuration defaults to use and the packages to install for the required dependencies. This opinionated approach helps in the fast setup of the projects.
  • Sprsetupoot lets you independently run your application without the need for a web server.

How is Spring Boot helpful to Java developers?

For one, Java developers using Spring Boot have it easier with the auto-configuration of all the components required to develop a production-grade Spring application. This, in the long run, reduces the development time and eventually boosts their efficiency.

Spring Boot also easily integrates with Spring’s ecosystem, which includes Spring JDBC, Spring Data, Spring Security, and the Spring ORM.

Java developers can also connect Spring Boot with different databases like Oracle, MySQL, PostgreSQL, and MongoDB, among others.

Of course, flexible configurations with XML configurations, Java Beans, and Database transactions are among other useful features.

Therefore, now that you have a basic overview of Spring Boot let us consider some of the frequently asked Spring Boot interview Questions and answers that will help you prepare for your interview.

Spring Boot Interview Questions and Answers

Spring  Boot interview questions

What are some features of Spring Boot?

Some of these popular features include:

  • The Spring Boot CLI provides Groovy for writing the Spring Boot application; in the long run, boilerplate code is avoided.
  • Spring Boot provides logging and a security feature that easily secures your application from potential security threats.
  • It provides auto-configuration of relevant components for your project, thus avoiding the risk of unnecessary WAR files.
  • The starter Initializer lays down a default internal project structure for you. This way, you do not have to manually set up the project structure.
  • The Spring Boot actuator feature gives access to insights and metrics as the application runs.
  • Of course, one of the key Spring Boot features, Starter Dependency, helps to aggregate a particular feature’s commonly used dependencies.

What are Spring Boot Starters?

Spring Boot starters are dependency descriptors that include a set of dependency management providers that enable the application’s dependencies. They provide the framework with Auto-Dependency Resolution. Starters enhance easy and rapid development.

What is an Actuator in Spring Boot, and what are its advantages?

The actuator is one of the Spring Boot features that lets you monitor what happens inside an application as it runs.

During debugging, for instance, you can use the actuator for analyzing logs by it allowing access to features like CPU usage and identification of beans.

Additionally, the actuator not only provides easy access to the production-ready REST endpoints, which monitor and manage information but also retrieves data from the web.

What is thymeleaf, and how to use thymeleaf?

Thymeleaf is Java’s server-side template that creates a natural template layout for both Spring and HTML5 Java web applications.

Spring Boot will perform an automatic configuration of thymeleaf using the spring-boot-starter-thymeleaf dependency in pom.xml file to serve the dynamic web content.

To allow Spring Boot to read and render the thymeleaf templates or HTML files, place the templates in src/main/resources/templates.

Thymeleaf then parses the index.html file and uses the actual values you pass from the controller class in place of the dynamic values available in the index file.

After this, the message renders in the web browser as soon as the Spring Boot application runs.

org.springframework.boot spring-boot-starter-thymeleaf

Describe the process of creating a Spring Boot project using Spring Initializer.

Spring Initializr, which is a Spring web tool, lets you create a Spring Boot project using a few steps by providing the details of the project.

  1. Head over to Spring intializr and fill in the input fields.
  2. Clicking the Generate button will start the project download.
  3. Extract the downloaded project from the zip file and open it from your IDE. From the IDE, navigate to File->New->Project from existing sources->Spring-boot-app, then select the pom.xml file. Click on the import changes prompt so that the project syncs. After this, remember to go to the application.properties file and edit the server.port number to server.port=7000.
  4. Now, run the application from src->main->java->com.gfg.Spring.boot.app

What is JPA in Spring Boot?

This is a specification in Java that uses Object-Relation Mapping(ORM) to manage relational data and allows access to data between the Java object or the Java class and the application’s relational database.

JPA uses the Java Persistent Query Language(JPQL), an object-oriented query language that is also platform-independent.

JPA allows query processing and object transactions against the database using the Entity Manager API it provides.

What is auto-configuration in Spring Boot?

Auto-configuration seeks to automate the Spring Boot application configuration using the jar dependencies you add to the applications.

Depending on the available dependencies in the Classpath of the application, auto-configuration will declare the spring-specific module’s built-in objects, including JPA, and spring security, among others.

What are Spring Annotations?

Spring annotations refer to metadata offering information about a program snippet, and they add supplemental data to that program. Code components, including classes and methods, are often associated with annotations.

Annotations do not directly affect the program’s operation or the compiled code’s subsequent action.
Their syntax begins with the ‘@‘ symbol.

Spring Boot provides six main annotations types that include:

  • Spring Core Annotations
  • Spring Data Annotations
  • Spring Bean Annotations
  • Spring Web Annotations
  • Spring Scheduling Annotations
  • Spring Boot Annotations

What does Spring Data REST mean?

Spring Data REST exposes the resources in RESTful that are around Spring Data Resources using minimal code.

The following example uses the POST method to request content using http://localhost/example as the URL and Content-Type: application/json as the Header.

Request Content:

{
    "name": "Jimmy",
    "Gender": "Male",
    "Age": 23
}

Response Content:

{
    "name": "Jimmy",
    "Gender": "Male",
    "Age": 23
    "_links": {
        "self": {
            "href": "http://localhost:8080/example/1"
        },
        "person": {
            "href": "http://localhost:8080/example/1"
         }
    }
}

What is the need for Spring Boot DevTools?

These are a profound set of predefined tools whose properties are applied to the respective development environments to make development easier and saves development time.

Whenever you change code in the Spring Boot application, the Spring Boot DevTools feature automatically restarts. Therefore, it saves you the trouble of manually restarting your application every time you alter your code.

What is Spring Data?

Spring data seeks to give developers easy access to data access technologies like relational and non-relational data and cloud-based data services as it continues to hold the underlying data store’s special traits.

How to tell an auto-configuration to back away when a bean exists?

Here you will be using the @ConditionalOnMissingBean annotation, which includes the name and value attribute as follows.

  • value attribute stores the bean type to check
  • name attribute that names the bean to check

How to fetch data from the database in Spring Boot?

We can access data from a MySQL database to our Spring Boot application using the following steps.

Step 1: Use the create DATABASE person command to create the database in MySQL.

Step 2: Within the database, create a table:

CREATE TABLE person(id INT PRIMARY KEY NOT NULL AUTO_INCREMENT, name VARCHAR(255));

Step 3: Now create a Spring Boot application, then add to it the JDBC, MySQL, and the required web dependencies.

Step 4: Configure the database from the application.properties file like below.

spring.datasource.url=jdbc:mysql://localhost:3306/personDetails
spring.datasource.username=example123
spring.datasource.password=example123
spring.jpa.hibernate.ddl-auto=create-drop

Step 5: Next, let’s handle requests in the controller class:

package com.person;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.jdbc.core.JdbcTemplate;
import org.springframework.web.bind.annotation.RestController;
@RestController
public class JdbcController {
   @Autowired
   JdbcTemplate jdbc;
   @RequestMapping("/save")
   public String index(){
      jdbc.execute("insert into person (name)values(Trial)");
      return "Name entered Successfully";
   }
}

Lastly, run your application as you check the database entry to see the data accessed.

Why do we need Spring Profiles?

Spring Profiles allow the segregation of an application’s configuration of different parts and avail them for specific developments.

Spring Profiles also saves the developer the pain of managing environment-specific external configurations if the Spring Profiles were not available.

Additionally, this would make it hard to keep in sync and would mean the extra need to write several factory-like components that would avail certain required things depending on particular environment-specific parameters.

Can we change the port of the embedded Tomcat server in Spring boot?

Yes, we can.

This is done by manipulating the application.properties file to include the server.port property and assigning to it a port of your choice. Spring Boot automatically loads the application properties file and applies the required configurations to the application.

For instance, you can change the server.port number from the default value of 8080 to server.port= 8081.

How do you configure Log4j for logging?

With these few simple steps, we can configure Log4j for logging:

  1. First, create your Java project, then right-click the project. Navigate to MyEclipse->File->New->Java Project to name the project and click finish.
  2. Next, right-click your Java project name and select Build Path -> Configure Build Path. This step will add the log4j file.
  3. Navigate to the library and click the Add External JARS button, and select the log4j file from the drop-down menu that appears. Then click OK.
  4. Create a new java file you will call log4j.properties file, then click finish and add this file to the Classpath.
  5. Click Advanced from the Classpath, then select the Add Folders option, and remember to click OK.
  6. You can now search for the log4j.properties file, click OK, and run the project.
  7. Check the console for the output below.
[main] DEBUG Example – Hello this is a debug message
[main] INFO Example – Hello this is an info message

What is an IoC Container?

The IoC(Inversion of Control) container is a core Spring container that automatically implements dependency injection. It instantiates the class’s application and is responsible for the objects’ configuration and assembling of the necessary dependencies.

It also manages the object’s life cycle from its instantiation to its destruction.

IoC performs these tasks using metadata configuration in Java code, XML, and Java annotations.

The container is referred to as an Inversion of Control because it controls the Java objects and these objects’ lifecycles. This is otherwise a developer’s task.

Explain how to create a Spring Boot application using Maven

This process entails a series of steps.

Step 1: Select the type of project.

Step 2: Name your project to configure it, then click the finish button to create the project.

Step 3: Now, we will configure the pom.xml file from the Maven project to create a Spring Boot project out of it.

pom.xml file:

<project xmlns="https://maven.apache.org/POM/4.0.0" xmlns:xsi="https://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="https://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">  
  <modelVersion>4.0.0</modelVersion>  
  <groupId>com.javatpoint</groupId>  
  <artifactId>spring-boot-example</artifactId>  
  <version>0.0.1-SNAPS<name>JavaTpoint Spring Boot Example</name>  
</project>  

The configuration involves the addition of a parent to the Maven project. This will declare the Maven project as a child project to the parent project.

<parent>  
    <groupId>org.springframework.boot</groupId>  
    <artifactId>spring-boot-starter-parent</artifactId>  
    <version>1.4.2.RELEASE</version>  
</parent>  

Step 4: Next, add the web dependency, spring-boot-starter-web, to the pom.xml.

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

Step 5: Add the project’s Java version.

<properties>  
    <java.version>1.8</java.version>  
</properties> 

Step 6: Note that every time you add new dependencies, you need to update the Maven project.

Step 7: Make the Maven project runnable by creating a Java class within the src/main/java package.

Step 8: Next, call the Spring Application’s class static run method.

Step 9: Lastly, run the class as a Java application.

What are the advantages of Spring Boot over Spring?

  • Spring Boot’s bootstrapping capability to compile the source language using Boot initializer, a technique called bootstrapping, allows space-saving on users’ devices and also reduces the application’s load time.
  • Unlike Spring, Spring Boot allows dependencies management after adding the spring-boot-dependencies without depending on the parent POM(parent object model) or XML file.
  • Spring Boot also allows developers to either use annotations or XML configurations without the need to use XML configurations.
  • Developers prefer Spring Boot for its decreased boilerplate code required to set up an application. This is because Spring Boot comes with an in-memory database and an embedded Tomcat server, decreasing the boilerplate code. Spring, on the other hand, has more boilerplate code.
  • Spring Boot does not necessarily require WAR(web application resource) files and can only rely on the JAR(Java Resource), which has a small and simpler structure and therefore is more useful to users and developers.
  • Spring Boot also automatically embeds servers like Tomcat and Jetty; therefore, the developer does not need to manually set up the server like you are supposed to do in Spring.

How to do pagination in Spring Boot?

The pagination process divides data into sections to save resources. It entails two fields, the page size, and the page number.

The process involves a few steps, including:

Step 1: Initial setup
Consisetupn entity we will name Person as the domain class.

@Entity 
public class Person {
    @Id
    private long id;
    private String name; 
}

Step 2: Repository creation
Next, use a PersonRepository extends PagingAndSortingRepository to be able to get the findAll(Pageable pageable) and findAll(Sort sort) methods for paging and sorting, respectively.

public interface PersonRepository extends PagingAndSortingRepository<Person, Integer> {
    List<Product> findAllByPrice(double price, Pageable pageable);
}

Step 3: Pagination step
The first step here involves creating a PageRequest object; by passing the page number and the page size as requested that implements the Pageable interface.

Pageable firstPageWithTwoElements = PageRequest.of(0,2);
Pageable secondPageWithThreeElements = PageRequest.of(1,3);

Then pass this PageRequest object to the repository method as a parameter.

Page<Person> allProducts = personRepository.findAllByPrice(findPageWithTwoElements);
List<Items> allTwoDollarItems = itemsRepository.findAllByPrice(2, secondPageThreeElements) 

By default, the findAll(Pageable pageable) method will return a Page<T> object.

Explain how to register a custom auto-configuration

Under the @EnableAutoConfiguration key META-INF/spring.factories file, mention the fully-qualified name. This step registers the auto-configuration class.

org.springframework.boot.autoconfigure.EnableAutoConfiguration=com.baeldung.autoconfigure.CustomAutoConfiguration

Building the project using Maven will require you to place the file in the resources/META-INF directory.

What is bootstrapping in Spring Boot?

Bootstrapping is the process of executing logic in the Spring Boot application on start-up.
The Boot initializr compiles the source language in Spring Boot. This process saves the device space and also reduces the application’s loading time.

Final Words 👨‍💻

Well, this article covered some Spring Boot questions interviewers will probably ask you during your interview and the answers to help you confidently ace it. We hope you land that dream job!

You may also want to learn a few relevant tips from questions asked during a Java interview.

Best of luck!🙂