Getting Started with Spring Boot: Your First "Hello, World!" REST API

👋 Introduction

Spring Boot makes it easy to create stand-alone, production-grade Spring applications with minimal setup. In this guide, you’ll learn how to build your first Spring Boot REST API that responds with a simple "Hello, World!".

---

🛠️ Step 1: Create a Spring Boot Project

The easiest way to generate a Spring Boot project is by using Spring Initializr:

🔧 Configuration:

• Project: Maven

• Language: Java

• Spring Boot: (Use the latest stable version)

• Dependencies: Spring Web

• Package name: com.helloworld or anything you would like

The configuration should look like this:

Click Generate, unzip the downloaded file, and open it in your favourite IDE (IntelliJ IDEA, Eclipse, VS Code). I prefer to use IntelliJ IDEA.

📁 Step 2: Understand the Project Structure

Spring Boot projects follow a standard structure:

src
└── main
├── java
│ └── com.helloworld
│ ├── HelloWorldApplication.java
└── resources
├── application.properties

• HelloWorldApplication.java is your entry point which contains a main method.

• We'll create a HelloWorldController.java to handle HTTP requests.

👨‍💻 Step 3: Create the Controller

Inside src/main/java/com/helloworld, create a file named HelloWorldController.java:

package com.helloworld;

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

@RestController
public class HelloWorldController {

    @GetMapping("/hello-world")
    public String helloWorld() {
        return "Hello, World!";
    }
}

• @RestController = @Controller + @ResponseBody

  • In Spring Boot, @RestController is a convenience annotation that combines two annotations:

    1. @Controller:

       • Marks the class as a Spring MVC controller that can handle HTTP requests.

       • By default, methods in a class annotated with @Controller return views (e.g., HTML pages via Thymeleaf or JSP).

       • If you return a string, it tries to resolve it as a view name — not ideal for REST APIs.

    2. @ResponseBody:

       • Tells Spring to write the method’s return value directly to the HTTP response body, instead of interpreting it as a view name.

       • Useful when you want to return plain text, JSON, or XML from a controller method.

So, when you write:

            @RestController
            public class HelloController {
                ...
            }

It’s functionally equivalent to:

            @Controller
            @ResponseBody
            public class HelloController {
                ...
            }

• @GetMapping("/hello") Maps GET Requests to /hello

  • @GetMapping("/hello") is a specialized version of the more generic @RequestMapping(method = RequestMethod.GET, path = "/hello").

  • It tells Spring to:

    • Map HTTP GET requests sent to the path /hello

    • To the Java method it annotates.

So, for this method:

        @GetMapping("/hello")
        public String helloWorld() {
            return "Hello, World!";
        }

When someone makes a GET request to http://localhost:8080/hello, Spring will:

1. Route the request to the helloWorld() method

2. Execute it

3. Return the response "Hello, World!" as the body of the HTTP response

▶️ Step 4: Run the Application

You can run your app in multiple ways:

📦 Using Maven:

./mvnw spring-boot:run

🧠 Or from your IDE:

Right-click on HelloWorldApplication.java → Run.

You’ll see logs ending with:

Tomcat started on port(s): 8080 (http)

8080 is the default port that spring boot uses to run the application. You can change it by setting following property in application.properties file:

server.port=9099

or in application.yml file:

server:
    port:9099

🌐 Step 5: Test the Endpoint

Open your browser or Postman and go to:

http://localhost:8080/hello-world

✅ Output:

Hello, World!

🧠 Bonus: What Just Happened?

• Spring Boot auto-configured an embedded Tomcat server.

• The @RestController handled your HTTP request.

• You didn’t need to write any XML configuration.

🧩 What’s Next?

Now that you’ve set up your first GET endpoint, here are a few ideas for the next steps:

• ✅ Accept query parameters

• ✅ Return JSON responses

• ✅ Add logging

• ✅ Connect to a database

🔚 Conclusion

You just created your first Spring Boot application with a simple REST endpoint. Spring Boot handles a lot of boilerplate for you so you can focus on building features.

You can find the complete code here: GitHub - AmanVW

Stay tuned for the next part in the series!

© Aman Walke