Java Spring Boot Interview Questions & Answers (2025)

Spring Boot is a system from "The Spring Team" to facilitate the bootstrapping and development of new Spring Applications. It gives defaults to code, and annotation configurations to snappy begin new spring projects at no time. It takes after the "Opinionated Defaults Configuration" Approach to escape from a lot of standard code and configuration to enhance Development, Unit Test, and Integration Test Process.

Here are some of the various advantages of using Spring Boot:

• It is quite easy to create Spring Based applications with Java or Groovy.
• It lessens lots of improvement time and expands profitability.
• It abstains from writing lots of standard Codes, Annotations, and XML Configuration.
• It is quite easy to coordinate Spring Boot Application with its Spring Ecosystem like Spring JDBC, Spring ORM, Spring Data, Spring Security and so forth.
• It takes after the "Opinionated Defaults Configuration" Approach to diminish Developer effort
• It gives Embedded HTTP servers like Tomcat, Jetty and more to create and test our web applications effectively.
• It gives CLI (Command Line Interface) tool to create and test Spring Boot (Java or Groovy) Applications from commanding prompt very easily and rapidly.
• It gives lots of modules to create and test Spring Boot Applications effectively utilizing Build Tools like Maven and Gradle
• It provides loads of plug-ins to work with implanted and in-memory Databases effortlessly.

Various Spring Boot Features are as follows:

• Web Development
• Spring Application
• Application occasions and listeners
• Admin highlights
• Externalized Configuration
• Properties Files
• YAML Support
• Type-safe Configuration
• Logging
• Security

The reason behind to have Spring-boot-maven module is it gives a couple of charges which empower you to package the code as a container or run the application

• spring-boot: run operates your Spring Boot application.
• spring-boot: repackage it repackages your jug/war to be executable.
• spring-boot: start and spring-boot: stop to deal with the lifecycle of your Spring Boot application (i.e., for joining tests).
• spring-boot: build-data creates build data that can be utilized by the Actuator.

The Spring Initializer is a web application that can produce a Spring Boot project structure for you. It doesn’t create any application code. However, it will give you an essential project structure and either a Maven or a Gradle build specification to fabricate your code with. You should simply compose the application code.

Spring Initializer can be utilized a few different ways, including:

• An online interface.
• Via Spring Tool Suite.
• Using the Spring Boot CLI.

Spring boot accompanies Dev Tools, which is acquainted with increase the profitability of designer. You don’t have to redeploy your application each time you influence the changes. The developer can reload the progressions without restart of the server. It maintains a strategic distance from the agony of redeploying application each time when you roll out any improvement. This module will can’t be utilized in a production environment.

Starters are an arrangement of advantageous reliance descriptors that you can incorporate into your application. The starters contain a considerable amount of the dependencies that you have to get a task up and running rapidly and with a steady, supported a set of managed transitive conditions.

The starter POMs are helpful reliance descriptors that can be added to your application’s Maven. In another word, if you are building up a project that utilizes Spring Batch for batch preparing, you need to incorporate spring-boot-starter-bunch that will import all the required conditions for the Spring Batch application. This decreases the burden of looking at and designing all of the conditions required for a structure.

Spring Boot Actuator is a sub-task of Spring Boot. It adds a few creation review administrations to your application with little exertion on your part. There are also has numerous features added to your application out-of-the-case for dealing with the administration in a production (or other) condition. They’re basically used to uncover diverse kinds of data about the running application – health, measurements, information, dump, env and so on.

The configuration record utilized as a part of spring boot ventures is an application. Properties. This record is imperative where we would overwrite all the default designs. Regularly we need to hold this document under the assets envelope of the project.

It takes after "Opinionated Defaults Configuration" Approach to lessen Developer exertion. Because of the Opinionated perspective of spring boot, what is required to begin yet additionally we can get out if not appropriate for the application. Spring Boot utilizes sensible defaults, “opinions,” for the most part in light of the classpath substance.

Spring Boot gives different properties, which can be indicated in our project’s application. Properties record. These properties have default values, and you can set that inside the properties record. Properties are utilized to set qualities like a server-port number, database association configuration and much more.

The configuration file name, which is utilized as a part of spring boot projects is application.properties. This document is very important where we would overwrite all the default setups. Ordinarily, we need to hold this document under the assets folder of the project.

No, it isn’t conceivable starting at now. Spring boot is restricted to Spring applications only.

Configuration file name which is utilized as a part of Spring boot ventures is known as application. Properties. It is vital to document as it is utilized to abrogate all default configurations.

Usage of spring security in Spring boot application requires quite a little configuration. You have to include spring-boot-starter-security starter in pom.xml. You need to make spring config class, which will expand WebSecurity Configure Adapter and override expected strategy to accomplish security in Spring boot application.

Yes, we can control logging with spring boot.

There is no force to go containerless

• The embedded container is only one component of Spring Boot
• Traditional WAR additionally benefits a considerable measure from Spring Boot
• Automatic Spring MVC setup, including Dispatcher Servlet
• Sensible defaults in light of the class-path content
• The embedded container can be utilized during improvement.

Spring Security is a groundbreaking and very adjustable authentication and access-control structure. It is the true standard for securing Spring-based applications. Spring Security is a system that spotlights on giving both authentication and approval to Java applications. Like all spring ventures, the genuine power of Spring Security is found in how effectively it can be reached out to meet custom prerequisites.

Aspect Oriented Programming (AOP) supplements Object-Oriented Programming (OOP) by giving another mindset about program structure. The key unit of measured quality in OOP is the class, while in AOP the unit of particularity is the viewpoint. Angles empower the modularization of concerns, for example, transaction management that cut over numerous sorts and questions.

Various spring sub-projects are as follows:

• JDBC: this module empowers a JDBC-deliberation layer that evaluates the need to do JDBC coding for particular vendor databases
  Read Best JDBC Interview Questions
• Core: a key module that gives basic parts of the system, such as IoC or DI
• Web: a web-situated joining module, giving multipart document upload, listeners members, and web-arranged application context functionalities
• ORM integration: gives mix layers to well-known protest object-relational mapping APIs, for example, JPA, JDO, and Hibernate
• AOP module: perspective oriented programming execution is permitting the meaning of clean strategy interceptors and pointcuts.
• MVC system: a web module executing the Model View Controller configuration design

JPA is a specification/Interface whereas Hibernate is one of the JPA implementations.

It is done in the following steps.

Step 1 -

The first step to connect the database like Oracle or MySql is adding the dependency for your database connector to pom.xml.

Step 2 -

The next step is the elimination of H2 Dependency from pom.xml

Step 3 -

Step 3 includes the schema and table to establish your database.

Step 4 -

The next step is configuring of the database by using Configure application.properties to connect to your database.

Step 5-

And the last step is to restart your device and your connection is ready to use.

/src/main/resources/static is the suggested folder for static content in Spring boot.

You can create a JS file for sending an alert by creating a custom file named custom.js in /src/main/resources/static/js/ directory with below code

alert("I'm active");

Spring Boot 1.5.10. RELEASE requires

• Java 7 +
• Spring 4.3.13 +

For build support

• Maven 3.2+
• Gradle 2.9+

Container Support

• Tomcat 7+
• Jetty 8+ (Jetty 9.3 requires JDK 8 +)

Autoconfiguration is way in Spring Boot to configure a spring application automatically on the basis of dependencies that are present on the classpath. It makes development easier and faster.

You can create a custom configuration for a MySQL data source in spring boot as

@Configuration 
public class MySQLAutoconfiguration {
 
//... 

}

You can enable auto-reload/LiveReload of spring boot application by adding the spring-boot-devtools dependency in the pom.xml file.

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-devtools</artifactId>
    <optional>true
</dependency>

Note: please restart your application for immediate effects.

You can enable HTTP/2 support in Spring Boot as follows: server.http2.enabled=true

Example:-

	
@Bean public ConfigurableServletWebServerFactory tomcatCustomizer() {

    TomcatServletWebServerFactory factory = new TomcatServletWebServerFactory(); 
   factory.addConnectorCustomizers(connector -> connector.addUpgradeProtocol(new Http2Protocol())); 

	return factory; 

}

To enable HTTP response compression in spring boot using GZIP you have to add below settings in your application.properties file.

# Enabling HTTP response compression in spring boot
server.compression.enabled=true
server.compression.min-response-size=2048
server.compression.mime-types=application/json,application/xml,text/html,text/xml,text/plain

Both @GetMapping and @RequestMapping are annotations for mapping HTTP GET requests onto specific handler methods in Spring boot. @GetMapping is a composed annotation that acts as a shortcut for @RequestMapping. @GetMapping is the newer annotation.

Actuator is a tool in Spring Boot for monitoring and managing our application. Actuator Monitors our app, gathers metrics, understands traffic or the state of our database. It uses HTTP endpoints or JMX beans to enable us to interact with it. An actuator is available to use from the first release of Spring Boot.

Here is a youtube video by Java Brains to understand Spring Boot Actuator

@SpringBootApplication annotation was introduced in Spring Boot version 1.2.0. It is a convenience annotation which is used in spring boot application to enable additions of beans using the classpath definitions.

You can configure error logging/debugging in Spring boot application by applying the following settings in application.properties or application.yml file.

logging.level.org.springframework.web: DEBUG
logging.level.org.hibernate: ERROR

Spring Boot Initilizr is a web interface which to rapidly create spring boot projects. Using this tool you can create Maven and Gradle projects. You can find Spring Boot Initilizr tool on https://start.spring.io/