Why annotations drive Spring Boot in Spring Boot - See It in Action

Why annotations drive Spring Boot

📖 Scenario: You are building a simple Spring Boot application to understand how annotations help configure and run the app without much boilerplate code.

🎯 Goal: Learn how to use key Spring Boot annotations to create a runnable application with a REST endpoint.

📋 What You'll Learn

Create a Spring Boot main application class with the correct annotation

Add a configuration variable for the server port

Create a REST controller class with a mapping annotation

Add the final annotation to enable component scanning and auto-configuration

💡 Why This Matters

🌍 Real World

Spring Boot is widely used to build web applications and microservices quickly with minimal setup.

💼 Career

Understanding annotations in Spring Boot is essential for Java developers working on backend services and enterprise applications.

1

Create the main Spring Boot application class

Create a public class called DemoApplication with a main method that calls SpringApplication.run(DemoApplication.class, args). Annotate the class with @SpringBootApplication.

Spring Boot

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

// Your code here

Need a hint?

The @SpringBootApplication annotation marks the main class and enables auto-configuration.

2

Add a configuration property for server port

Create a String variable called serverPort and set it to "8081" inside the DemoApplication class.

Spring Boot

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

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

    // Add a String variable called serverPort and set it to "8081"
    // Your code here
}

Need a hint?

This variable simulates a configuration property for the server port.

3

Create a REST controller with a GET mapping

Create a public class called HelloController annotated with @RestController. Inside it, create a method sayHello that returns "Hello, Spring Boot!" and annotate it with @GetMapping("/hello").

Spring Boot

import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

// Create HelloController class with @RestController annotation
// Add sayHello method with @GetMapping("/hello") that returns "Hello, Spring Boot!"
// Your code here

Need a hint?

The @RestController annotation makes the class a web controller, and @GetMapping maps HTTP GET requests.

4

Add final annotation to enable auto-configuration

Ensure the DemoApplication class is annotated with @SpringBootApplication to enable component scanning and auto-configuration.

Spring Boot

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

// Confirm @SpringBootApplication annotation is present on DemoApplication
// Your code here

Need a hint?

This annotation is the key to Spring Boot's auto-configuration magic.