Building a REST API with Spring Boot

Spring Boot is an excellent tool for quickly developing RESTful web services. In this article, we’ll walk through creating a REST API step by step using Spring Boot.

🌟 What is a REST API?

REST (Representational State Transfer) is an architectural style for designing web services. It uses standard HTTP methods for communication between clients and servers.

HTTP Methods

🛠️ Step 1: Create a Project

You can create a Spring Boot project using Spring Initializr. Select the following settings:

• Project: Maven
• Language: Java or Kotlin
• Spring Boot Version: 3.0.0+
• Dependencies: Spring Web, Spring Boot DevTools, Lombok

Download the project, open it in your IDE, and get ready to run it.

📖 Step 2: Create a Model Class

Create a model class for a Todo object:

• Java
• Kotlin

package com.example.demo.model;

import lombok.Data;

@Data
public class Todo {
    private Long id;
    private String title;
    private boolean completed;
}

package com.example.demo.model

data class Todo(
    var id: Long,
    var title: String,
    var completed: Boolean
)

📘 Step 3: Create a Controller Class

Add a TodoController class to define CRUD operations as REST endpoints:

• Java
• Kotlin

package com.example.demo.controller;

import com.example.demo.model.Todo;
import org.springframework.web.bind.annotation.*;

import java.util.ArrayList;
import java.util.List;

@RestController
@RequestMapping("/api/todos")
public class TodoController {

    private List<Todo> todos = new ArrayList<>();

    @GetMapping
    public List<Todo> getAllTodos() {
        return todos;
    }

    @PostMapping
    public Todo createTodo(@RequestBody Todo todo) {
        todo.setId((long) (todos.size() + 1));
        todos.add(todo);
        return todo;
    }

    @PutMapping("/{id}")
    public Todo updateTodo(@PathVariable Long id, @RequestBody Todo updatedTodo) {
        Todo todo = todos.stream().filter(t -> t.getId().equals(id)).findFirst().orElse(null);
        if (todo != null) {
            todo.setTitle(updatedTodo.getTitle());
            todo.setCompleted(updatedTodo.isCompleted());
        }
        return todo;
    }

    @DeleteMapping("/{id}")
    public void deleteTodo(@PathVariable Long id) {
        todos.removeIf(todo -> todo.getId().equals(id));
    }
}

package com.example.demo.controller

import com.example.demo.model.Todo
import org.springframework.web.bind.annotation.*

@RestController
@RequestMapping("/api/todos")
class TodoController {

    private val todos = mutableListOf<Todo>()

    @GetMapping
    fun getAllTodos(): List<Todo> = todos

    @PostMapping
    fun createTodo(@RequestBody todo: Todo): Todo {
        todo.id = (todos.size + 1).toLong()
        todos.add(todo)
        return todo
    }

    @PutMapping("/{id}")
    fun updateTodo(@PathVariable id: Long, @RequestBody updatedTodo: Todo): Todo? {
        val todo = todos.find { it.id == id }
        todo?.apply {
            title = updatedTodo.title
            completed = updatedTodo.completed
        }
        return todo
    }

    @DeleteMapping("/{id}")
    fun deleteTodo(@PathVariable id: Long) {
        todos.removeIf { it.id == id }
    }
}

▶️ Step 4: Test the API

Test your API using curl commands:

• GET All Todos:

curl -X GET http://localhost:8080/api/todos

• POST New Todo:

curl -X POST http://localhost:8080/api/todos -H "Content-Type: application/json" -d '{"title": "New Todo", "completed": false}'

• PUT Update Todo:

curl -X PUT http://localhost:8080/api/todos/1 -H "Content-Type: application/json" -d '{"title": "Updated Todo", "completed": true}'

• DELETE Delete Todo:

curl -X DELETE http://localhost:8080/api/todos/1

By following these steps, you’ll have built a REST API with Spring Boot.