Spring Boot Interview Questions

Spring Boot is an open-source Java-based framework used to create stand-alone, production-grade Spring-based applications. It is a project within the larger Spring Framework ecosystem, designed to simplify the setup, configuration, and deployment of Spring applications. Spring Boot is highly popular for its ability to enable developers to build applications quickly with minimal boilerplate code and configurations.

Main Features of Spring Boot

1. Auto-Configuration:

   • Spring Boot can automatically configure your application based on the dependencies you have added to the project.
   • This feature reduces the need for extensive configuration files (e.g., XML).

2. Standalone Applications:

   • Spring Boot applications are typically packaged as self-contained JAR files with an embedded web server (such as Tomcat, Jetty, or Undertow).
   • This makes it easy to deploy and run applications with minimal setup.

3. Spring Initializr:

   • A web-based tool (available at start.spring.io) that allows you to generate a Spring Boot project with dependencies pre-configured.
   • You can choose the required dependencies, project metadata, and generate a ready-to-use project.

4. Production-Ready Features:

   • Spring Boot includes several features to help you build production-ready applications, such as metrics, health checks, and externalized configuration.
   • The Actuator module provides endpoints for monitoring and managing your application.

5. Opinionated Defaults:

   • Spring Boot follows convention over configuration, providing sensible defaults to speed up development.
   • It pre-configures many aspects of the application to help developers get started quickly.

6. Embedded Web Server:

   • Supports embedded web servers like Tomcat, Jetty, and Undertow, allowing you to run web applications without needing to deploy to an external server.
   • You can switch the embedded server or customize its configuration easily.

7. Spring Boot Starters:

   • Starters are a set of convenient dependency descriptors that you can include in your project. They bring in all the necessary dependencies for a particular functionality (e.g., spring-boot-starter-web for web applications).
   • This simplifies dependency management by bundling common dependencies into a single starter.

8. Externalized Configuration:

   • Supports externalized configuration via properties or YAML files, environment variables, and command-line arguments.
   • This allows you to have different configurations for different environments (e.g., development, staging, production).

9. Microservices Support:

   • Spring Boot is often used to develop microservices due to its simplicity and production-ready features.
   • Integrates well with Spring Cloud to provide solutions for distributed systems, including configuration management, service discovery, and circuit breakers.

10. Testing Support:

    • Provides comprehensive support for testing Spring applications, including utilities and annotations to simplify writing unit and integration tests.
    • Built-in support for mocking, web tests, and loading specific application contexts for tests.

Example of a Simple Spring Boot Application

Step 1: Create a Spring Boot Project

You can create a new Spring Boot project using Spring Initializr (https://start.spring.io).

1. Go to https://start.spring.io.
2. Choose your project metadata (e.g., group, artifact, name).
3. Select dependencies such as Spring Web for a web application.
4. Generate and download the project.

Step 2: Write a Simple Controller

Create a simple REST controller to handle HTTP requests.

package com.example.demo;

import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class HelloController {

    @GetMapping("/hello")
    public String hello() {
        return "Hello, Spring Boot!";
    }
}

Step 3: Run the Application

Run the application using your IDE or command line:

./mvnw spring-boot:run
# or
./gradlew bootRun

Alternatively, you can package the application as a JAR and run it:

./mvnw package
java -jar target/demo-0.0.1-SNAPSHOT.jar

Visit http://localhost:8080/hello in your browser to see the output.

Summary

• Spring Boot: A framework that simplifies the development of Spring-based applications by providing auto-configuration, embedded servers, and opinionated defaults.
• Main Features:
  • Auto-Configuration
  • Standalone Applications
  • Spring Initializr
  • Production-Ready Features (Actuator)
  • Opinionated Defaults
  • Embedded Web Server
  • Spring Boot Starters
  • Externalized Configuration
  • Microservices Support
  • Testing Support

Spring Boot is designed to streamline the development process, allowing developers to focus on writing business logic while the framework handles the infrastructure and configuration details.