Spring Boot 3 Tutorial for Beginners: Build Your First REST API

Introduction

Spring Boot has become the most popular framework for building modern Java applications. It simplifies Java development by reducing configuration, providing embedded servers, and offering production-ready features out of the box.

In this tutorial, you will learn how to create your first Spring Boot 3 REST API step by step. By the end of this guide, you'll have a running web service that returns data through HTTP requests.

Whether you're a student, beginner Java developer, or someone transitioning from Servlets and JSP, this tutorial will help you get started with Spring Boot development.

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What is Spring Boot?

Spring Boot is an open-source Java framework built on top of the Spring Framework. It simplifies application development by providing:

• Auto Configuration
• Embedded Tomcat Server
• Starter Dependencies
• Production-ready Features
• Simplified Project Setup

Instead of spending hours configuring XML files and application servers, developers can focus on writing business logic.

Benefits of Spring Boot

• Faster development
• Reduced configuration
• Easy dependency management
• Microservices support
• Cloud-ready applications
• Large community support

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Prerequisites

Before starting, make sure you have:

• Java 17 or later installed
• Maven installed
• IntelliJ IDEA or Eclipse
• Basic Java knowledge

You can verify Java installation using:

java -version

Example output:

openjdk version "17.0.10"

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Creating a Spring Boot Project

The easiest way to create a Spring Boot project is using Spring Initializr.

Project Configuration

Choose:

Project: Maven
Language: Java
Spring Boot: 3.x
Group: com.javawebaction
Artifact: springbootdemo
Packaging: Jar
Java: 17

Dependencies

Add:

Spring Web
Spring Boot DevTools

Click Generate and download the project.

Open the project in your IDE.

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Understanding the Project Structure

After importing the project, you'll see a structure similar to this:

springbootdemo
 ├── src
 │   ├── main
 │   │   ├── java
 │   │   └── resources
 │   └── test
 ├── pom.xml
 └── mvnw

Important Files

pom.xml

Contains project dependencies.

application.properties

Stores application configuration.

Main Application Class

This is the starting point of the application.

Example:

@SpringBootApplication
public class SpringbootdemoApplication {

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

}

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Creating Your First REST Controller

Create a new package:

com.javawebaction.controller

Inside the package, create:

package com.javawebaction.controller;

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

@RestController
public class WelcomeController {

    @GetMapping("/")
    public String welcome() {
        return "Welcome to Java Web Action Spring Boot Tutorial";
    }

}

Explanation

@RestController

Marks the class as a REST Controller.

@GetMapping

Maps HTTP GET requests.

welcome()

Returns a simple response to the browser.

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Running the Application

Run the main application class.

You should see output similar to:

Tomcat started on port(s): 8080
Started SpringbootdemoApplication

Spring Boot automatically starts an embedded Tomcat server.

No external server installation is required.

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Testing the REST API

Open your browser and visit:

http://localhost:8080

Output:

Welcome to Java Web Action Spring Boot Tutorial

Congratulations!

You have successfully created your first Spring Boot REST API.

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Returning JSON Response

REST APIs commonly return JSON data.

Update the controller:

package com.javawebaction.controller;

import java.util.HashMap;
import java.util.Map;

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

@RestController
public class WelcomeController {

    @GetMapping("/api")
    public Map<String, String> apiResponse() {

        Map<String, String> response = new HashMap<>();

        response.put("status", "success");
        response.put("message", "Spring Boot API is running");

        return response;
    }
}

Visit:

http://localhost:8080/api

Response:

{
  "status": "success",
  "message": "Spring Boot API is running"
}

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Common Errors and Solutions

Port Already in Use

Error:

Port 8080 was already in use

Solution:

Change port in:

server.port=9090

Dependency Download Issues

Run:

mvn clean install

to download all dependencies.

Java Version Error

Ensure your project uses Java 17 or later.

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Best Practices

When working with Spring Boot:

• Use meaningful package names
• Keep controllers lightweight
• Separate business logic into services
• Use DTOs for API responses
• Follow REST standards
• Use proper exception handling

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Frequently Asked Questions (FAQ)

Is Spring Boot easier than Spring Framework?

Yes. Spring Boot removes much of the configuration required by traditional Spring applications.

Do I need Tomcat separately?

No. Spring Boot includes an embedded Tomcat server.

Which Java version should I use?

Spring Boot 3 officially supports Java 17 and newer versions.

Is Spring Boot used in real companies?

Yes. Many startups and enterprise organizations use Spring Boot for backend and microservices development.

Can Spring Boot be used for Microservices?

Absolutely. Spring Boot is one of the most popular frameworks for building microservices.

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Conclusion

Spring Boot makes Java development faster, simpler, and more productive. In this tutorial, you learned how to create a Spring Boot project, build a REST controller, run an embedded server, and return both text and JSON responses.

This is just the beginning of your Spring Boot journey. In the next tutorial, we will create a more practical REST API and connect it with a database.