Introduction to Spring Boot

What is Spring Boot?

Spring Boot is an extension of the Spring Framework that removes the boilerplate configuration needed to build production-ready Spring applications. It follows an opinionated, convention-over-configuration approach.

Core ideas:

• Auto-configuration — Spring Boot guesses sensible defaults based on the dependencies on your classpath (e.g. add spring-boot-starter-web and it configures an embedded Tomcat + Spring MVC automatically).
• Starter dependencies — curated dependency bundles (spring-boot-starter-*) that pull in everything needed for a feature (web, data-jpa, security, test...).
• Embedded servers — Tomcat/Jetty/Undertow ships inside the JAR, so you run java -jar app.jar instead of deploying a WAR to an external server.
• Production-ready features — metrics, health checks, externalized config via Actuator (covered later).

Why Spring Boot over plain Spring?

The Big Picture: Spring vs Spring Boot vs Spring MVC

• Spring Framework — the core: IoC container, dependency injection, AOP.
• Spring MVC — a module built on Spring for building web apps/REST APIs (DispatcherServlet, controllers, view resolvers).
• Spring Boot — a layer on top of both that auto-configures and packages everything so you can run a Spring app with minimal setup.

A Minimal Spring Boot App

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

@SpringBootApplication is a meta-annotation combining:

• @Configuration — marks the class as a source of bean definitions.
• @EnableAutoConfiguration — turns on auto-configuration.
• @ComponentScan — scans the current package (and sub-packages) for components.

Key Terms to Know Before Moving On

• Bean — an object managed by the Spring IoC container.
• Application Context — the container that holds and wires beans.
• Auto-configuration class — a class annotated with @Configuration that conditionally registers beans (e.g. DataSourceAutoConfiguration).
• Starter POM — a Maven/Gradle dependency that transitively pulls in a feature's dependencies.