Plain Spring gives you huge flexibility but requires a lot of manual XML/Java configuration. Spring Boot layers auto-configuration, starter dependencies and an embedded server on top, so a working app can be running in minutes.

• Auto-configuration — sensible defaults based on what's on the classpath
• Starter dependencies — one dependency pulls in everything a feature needs
• Embedded server — Tomcat/Jetty/Undertow bundled in, no separate deploy step
• Production-ready features — health checks and metrics via Actuator

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