Spring Boot Introduction

Introduction

Spring Boot is an opinionated layer on top of the Spring Framework that removes 90% of the boilerplate Spring used to require. It bundles an embedded Tomcat/Jetty/Undertow server, auto-configures common components, and lets you ship a runnable JAR with one command: java -jar app.jar.

Where classic Spring needed XML and 30 lines of config to expose a single endpoint, Spring Boot needs three annotations.

Understanding the topic

What Spring Boot solves:

• Auto-configuration — sees you have spring-data-jpa + H2 on classpath → wires DataSource, EntityManager, transaction manager automatically.
• Starters — curated dependency bundles (spring-boot-starter-web, -data-jpa, -security) with versions that work together.
• Embedded server — no WAR, no external Tomcat. The JAR is the server.
• Production-ready — Actuator endpoints (/health, /metrics) ship out of the box.
• Convention over configuration — sensible defaults you can override.

Informative example

A complete Spring Boot REST API in 12 lines:

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

  @GetMapping("/hello")
  public Map<String, String> hello() {
    return Map.of("message", "Hello, backend world!");
  }
}

Real-world use

Spring Boot's auto-configuration + starter model is why teams at scale (Netflix, ING Bank, eBay) can spin up new microservices in hours, not weeks. Standardised dependencies = fewer bugs at the seams between services.

Best practices

• Use Spring Initializr (start.spring.io) to bootstrap every project.
• Pin the Spring Boot version in your parent POM — let it manage transitive versions.
• Don't fight the framework: if you're writing 200 lines of config, you're missing a starter.