Introduction to Spring Framework and Spring Boot

Table of Contents

1. What is the Spring Framework?
2. Why Use Spring?
3. Core Concepts of Spring Framework
   • Inversion of Control (IoC)
   • Dependency Injection (DI)
   • Aspect-Oriented Programming (AOP)
4. Spring Modules Overview
5. Spring vs Traditional Java Development
6. Introduction to Spring Boot
7. Benefits of Spring Boot
8. Spring Boot Architecture
9. Key Annotations in Spring and Spring Boot
10. Spring Boot CLI and Initializr
11. Comparison: Spring vs Spring Boot
12. Conclusion

1. What is the Spring Framework?

Spring Framework is a powerful, feature-rich, and modular Java framework designed for building enterprise-level applications. It simplifies Java development by offering a comprehensive programming and configuration model for modern Java-based enterprise applications.

It is widely used to build web applications, RESTful APIs, microservices, data access layers, and more — and serves as a foundation for numerous other frameworks like Spring Boot, Spring Security, Spring Data, and Spring Cloud.

2. Why Use Spring?

Traditional Java development (especially with JEE/Java EE) can be cumbersome due to boilerplate code, tightly coupled components, and complex configurations.

Spring addresses these issues by:

• Reducing boilerplate code using Dependency Injection
• Supporting Aspect-Oriented Programming (AOP)
• Providing integration with other frameworks (Hibernate, JPA, JMS)
• Offering modularity and testability
• Supporting both XML and annotation-based configurations
• Simplifying unit testing via loose coupling

3. Core Concepts of Spring Framework

3.1 Inversion of Control (IoC)

IoC is a design principle where control of object creation and management is transferred from the program to the Spring container. This means you don’t instantiate classes directly; instead, Spring does it for you.

3.2 Dependency Injection (DI)

DI is the mechanism by which Spring achieves IoC. It allows you to inject dependencies (objects) into classes through:

• Constructor injection
• Setter injection
• Field injection

Example:

javaCopyEdit@Component
public class Car {
    private Engine engine;

    @Autowired
    public Car(Engine engine) {
        this.engine = engine;
    }
}

3.3 Aspect-Oriented Programming (AOP)

AOP enables separation of cross-cutting concerns (like logging, security, transactions) from business logic. Spring AOP allows you to define these concerns in reusable modules.

Example: Logging logic can be separated from core business logic and executed before/after certain methods using aspects.

4. Spring Modules Overview

Spring is divided into multiple modules such as:

• Spring Core: IoC and DI container
• Spring AOP: Aspect-oriented programming support
• Spring Data: Access and manage relational and NoSQL databases
• Spring MVC: Build web applications
• Spring Security: Authentication and authorization
• Spring Boot: Simplified Spring application setup and deployment

5. Spring vs Traditional Java Development

6. Introduction to Spring Boot

Spring Boot is an extension of the Spring Framework that simplifies the setup, configuration, and deployment of Spring applications. It eliminates boilerplate code and offers out-of-the-box features like:

• Embedded servers (Tomcat, Jetty)
• Auto-configuration
• Production-ready metrics and monitoring
• Opinionated starter dependencies

You can create a Spring Boot app with minimal setup and get running quickly, even for complex applications.

7. Benefits of Spring Boot

• No XML Configuration: Uses annotations and .properties/.yml files
• Standalone Applications: Run with java -jar command
• Embedded Servers: No need to deploy on external servers
• Auto-Configuration: Sensible defaults reduce manual configuration
• Spring Boot Starters: Pre-packaged dependencies for specific functionalities (e.g., spring-boot-starter-web, spring-boot-starter-data-jpa)
• DevTools: Built-in tools for hot reloading and faster development

8. Spring Boot Architecture

Spring Boot is built on top of the Spring framework. Key architectural components include:

• Spring Boot Starters: Dependency descriptors to simplify Maven/Gradle setup
• Spring Boot Auto Configuration: Automatically configures beans based on the classpath
• Spring Boot CLI: A command-line interface to run and test Spring Boot applications
• Embedded Web Servers: Tomcat/Jetty/Undertow bundled with the app

9. Key Annotations in Spring and Spring Boot

• @Component / @Service / @Repository: Marks classes as beans managed by Spring
• @Autowired: Injects dependencies automatically
• @Configuration: Declares a class as a source of bean definitions
• @Bean: Declares a bean method
• @SpringBootApplication: Combines @Configuration, @EnableAutoConfiguration, and @ComponentScan
• @RestController: Defines a REST controller
• @RequestMapping / @GetMapping / @PostMapping: Maps HTTP requests to handler methods

10. Spring Boot CLI and Initializr

Spring Boot CLI:

A tool to rapidly prototype applications using Groovy.

bashCopyEditspring run app.groovy

Spring Initializr:

A web-based tool to bootstrap a Spring Boot project.

• Website: https://start.spring.io
• Choose project metadata, dependencies, and generate the project structure.

11. Comparison: Spring vs Spring Boot

12. Conclusion

Spring Framework and Spring Boot are cornerstones of modern Java development. While Spring provides a flexible foundation for building enterprise applications, Spring Boot makes development faster and simpler through auto-configuration and production-ready defaults. Together, they form a powerful toolkit for building robust, scalable, and maintainable Java applications.

As you proceed with Spring development, focus first on mastering dependency injection, annotation-based configuration, and Spring Boot project setup. These are the foundation blocks that will make the rest of the journey seamless.