Spring Boot Handbook

First, the Basics

• Spring Framework (a.k.a Spring):
  A comprehensive framework for building Java applications.
  It provides dependency injection, aspect-oriented programming, data access, web MVC, security, etc.
  But it requires a lot of manual configuration.

• Spring Boot:
  A framework built on top of Spring that makes development faster, easier, and less error-prone by removing configuration overhead.
  It comes with auto-configuration, starter dependencies, embedded servers, and production-ready features.

• Spring = Buying raw ingredients and cooking everything yourself.

• Spring Boot = Ordering a ready-made meal kit that comes pre-measured, half-cooked, and ready in 10 minutes.

Key Differences 

Example — Building a Simple REST API

(A) Using Spring Framework

Steps:

1. Configure DispatcherServlet in web.xml.

2. Set up Spring Beans in applicationContext.xml.

3. Configure Tomcat/Jetty server.

4. Create Controller.

<!-- web.xml -->
<web-app>
  <servlet>
    <servlet-name>dispatcher</servlet-name>
    <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
    <load-on-startup>1</load-on-startup>
  </servlet>
  <servlet-mapping>
    <servlet-name>dispatcher</servlet-name>
    <url-pattern>/</url-pattern>
  </servlet-mapping>
</web-app>

<!-- web.xml -->
<web-app>
  <servlet>
    <servlet-name>dispatcher</servlet-name>
    <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
    <load-on-startup>1</load-on-startup>
  </servlet>
  <servlet-mapping>
    <servlet-name>dispatcher</servlet-name>
    <url-pattern>/</url-pattern>
  </servlet-mapping>
</web-app>

@Controller
public class HelloController {
    @RequestMapping("/hello")
    @ResponseBody
    public String sayHello() {
        return "Hello from Spring!";
    }
}

Needs external Tomcat, WAR deployment.

(B) Using Spring Boot

Steps:

1. Add spring-boot-starter-web dependency.

2. Write Controller.

3. Run the app.

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

@RestController
public class HelloController {
    @GetMapping("/hello")
    public String sayHello() {
        return "Hello from Spring Boot!";
    }
}

Just run → http://localhost:8080/hello works immediately. No XML. No server setup.

When to Use What?

• Use Spring Framework when:

  • You need fine-grained control over every bean and configuration.

  • You’re working on large legacy enterprise systems that still follow WAR deployment.

  • You want flexibility over conventions.

• Use Spring Boot when:

  • You want rapid development (REST APIs, microservices).

  • You’re deploying to cloud-native environments (Docker, Kubernetes).

  • You want production-ready features out of the box.

Conclusion

• Spring = Foundation (powerful but configuration-heavy).

• Spring Boot = Accelerator (removes boilerplate, adds auto-magic).

• Spring Boot saves time, reduces errors, and is ideal for modern cloud-based apps.

• Example proves: Boot = 5 lines of code vs. Spring = multiple XMLs + configs.

Think of Spring as the “engine” and Spring Boot as the “car”. You can build your own car from scratch with just the engine (Spring), but Boot gives you a ready-to-drive car.