What is Spring Boot and how does it simplify Spring applications?

Spring Boot does not replace Spring; it configures it. Auto-configuration inspects the classpath and existing beans, then supplies sensible defaults. Starters bundle compatible dependencies, and the embedded server means the application runs from a main method without an external container.

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

The pieces that matter

• Starters such as spring-boot-starter-web and spring-boot-starter-data-jpa
• Embedded Tomcat, Jetty or Undertow, configured through properties
• Actuator endpoints for health, metrics and environment inspection
• Profiles for environment-specific configuration
• A fat jar that contains the application and its dependencies

Convention over configuration is the point, but defaults must be understood. Auto-configuration backs off when you define your own bean of the relevant type. You can exclude a configuration or override properties when the default does not fit.