Building Your First REST API in Spring Boot

Spring Boot offers a powerful and minimalistic way to build modern REST APIs in Java. Whether you’re just getting started with backend development or coming from a different stack, Spring Boot simplifies a lot of the boilerplate code.

In this guide, you’ll learn how to create First REST API in Spring Boot :

Set up a Spring Boot project
Create a simple RESTful controller
Handle basic CRUD operations (GET, POST, PUT, DELETE)
Test the API using Postman or curl

Let’s begin! 🚀

Building Your First REST API in Spring Boot

✅ What is a REST API?

REST (Representational State Transfer) is an architectural style that uses standard HTTP methods like:

GET — retrieve data
POST — create new data
PUT — update existing data
DELETE — remove data

Spring Boot makes it easy to implement these with annotations like @RestController, @GetMapping, @PostMapping, etc.

⚙️ Step 1: Project Setup Using Spring Initializr

Go to https://start.spring.io and configure:

Project: Maven
Language: Java
Spring Boot: Latest stable version
Group: com.kscodes.springboot
Artifact: firstapp
Dependencies:
- Spring Web
- Spring Boot DevTools (optional for auto-reload)
- Lombok (optional for boilerplate reduction)

Click Generate, unzip the file, and open the project in your IDE (IntelliJ or Eclipse).

🗂️ Step 2: Project Structure

src/

└── main/

├── java/

│ └── com/kscodes/springboot/firstapp/

│ ├── FirstAppApplication.java

│ ├── controller/

│ ├── model/

│ └── service/ (optional for future enhancements)

└── resources/

└── application.properties

📦 Step 3: Create the User Model

package com.kscodes.springboot.firstapp.model;

public class User {

private Long id;

private String name;

private String email;

public User() {}

public User(Long id, String name, String email) {

this.id = id;

this.name = name;

this.email = email;

}

public Long getId() { return id; }

public void setId(Long id) { this.id = id; }

public String getName() { return name; }

public void setName(String name) { this.name = name; }

public String getEmail() { return email; }

public void setEmail(String email) { this.email = email; }

}

🔧 Step 4: Create the User Controller

package com.kscodes.springboot.firstapp.controller;

import com.kscodes.springboot.firstapp.model.User;

import org.springframework.web.bind.annotation.*;

import java.util.*;

@RestController

@RequestMapping("/api/users")

public class UserController {

private Map<Long, User> users = new HashMap<>();

private Long idCounter = 1L;

// GET all users

@GetMapping

public List<User> getAllUsers() {

return new ArrayList<>(users.values());

}

// GET user by ID

@GetMapping("/{id}")

public User getUserById(@PathVariable Long id) {

return users.get(id);

}

// POST new user

@PostMapping

public User createUser(@RequestBody User user) {

user.setId(idCounter++);

users.put(user.getId(), user);

return user;

}

// PUT update user

@PutMapping("/{id}")

public User updateUser(@PathVariable Long id, @RequestBody User updatedUser) {

User existing = users.get(id);

if (existing != null) {

existing.setName(updatedUser.getName());

existing.setEmail(updatedUser.getEmail());

}

return existing;

}

// DELETE user

@DeleteMapping("/{id}")

public String deleteUser(@PathVariable Long id) {

users.remove(id);

return "User with ID " + id + " deleted.";

}

▶️ Step 5: Run the Application

Run the main class:

package com.kscodes.springboot.firstapp;

import org.springframework.boot.SpringApplication;

import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication

public class FirstAppApplication {

public static void main(String[] args) {

SpringApplication.run(FirstAppApplication.class, args);

}

🧪 Step 6: Test the API

You can test the API using Postman, curl, or any HTTP client.

🔹 Get All Users

GET http://localhost:8080/api/users

🔹 Create a User

1	<br>POST http://localhost:8080/api/users<br>Content-Type: application/json<br><br>{<br> "name": "John Doe",<br> "email": "john@example.com"<br>}<br><br><br>

🔹 Get User by ID

GET http://localhost:8080/api/users/1

🔹 Update a User

PUT http://localhost:8080/api/users/1

Content-Type: application/json

{

"name": "John S Doe",

"email": "new@example.com"

}

🔹 Delete a User

DELETE http://localhost:8080/api/users/1

✅ Summary

You’ve successfully created your First REST API in Spring Boot that:

Uses an in-memory map for storing users
Supports full CRUD operations
Can be extended to use databases or services in the future