Introduction

🌱 What is Spring?

Spring is a powerful, lightweight Java framework used for building enterprise-level applications.

✅ Key Features:

1. Dependency Injection (IoC): Promotes loose coupling between classes

2. Aspect-Oriented Programming (AOP): Helps separate cross-cutting concerns like logging or security

3. Modular: You can use just what you need (Spring Core, Spring MVC, etc.)

4. Testable: Makes writing unit and integration tests easier

5. Spring provides the foundational tools to build robust and maintainable Java applications.

🚀 What is Spring Boot?

Spring Boot is a tool built on top of Spring that simplifies application development.

✅ Key Features:

1. Auto-configuration: Reduces boilerplate code and configuration

2. Standalone: Easily run apps without needing an external server (uses embedded Tomcat/Jetty)

3. Production-ready: Includes built-in metrics, health checks, logging, etc.

4. Opinionated defaults: Comes with sensible defaults for rapid development

5. Think of Spring Boot as the fastest way to get a Spring application up and running.

🔄 Spring vs Spring Boot

Feature	Spring (Core)	Spring Boot
Setup	Manual configuration	Minimal setup with auto-configuration
Web Server	Needs external configuration	Comes with embedded Tomcat/Jetty
Dependencies	Needs to be managed manually	Managed automatically via starters
Learning Curve	Steeper	Easier for beginners
Use Case	Full control, large enterprise apps	Rapid development, microservices, REST APIs

🧪 Example

Spring Boot Hello World

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

This alone starts a full web app with embedded server — no web.xml, no complex config.